Examination Of The Patient And External Examination Of The Eye; Functional Testing
Examination Of The Patient And External Examination Of The Eye; Functional TestingBy G. E. De Schweinitz, A. M., M. D., of PHILADELPHIA
THE value of case records is greatly enhanced if a systematic method of examination is pursued with each patient. The following order of examination, based upon the one employed by S. Weir Mitchell in the Infirmary for Nervous Diseases, Philadelphia, is arranged for this purpose:
Name and residence
Age, sex, race, married, single, or widowed
Family history: hereditary tendencies; general and ocular health of parents, brothers, sisters, etc.
Personal history: children, their general and ocular health; miscarriages; meno former illnesses; syphilis and gonorrhea; injuries.
Occupation : relation of work to present indisposition.
Habits: brain use; tobacco; alcohol; narcotics; sexual.
Date and mode of onset and supposed cause of present trouble; outline of its course. Organs of digestion: teeth; tongue; stomach; bowels.
Organs of respiration: nose; throat ; lungs.
Organs of circulation: heart; pulse; blood.
Kidneys: examination of urine.
Abdominal organs: liver; spleen.
Organs of generation: menses; leucorrhoea; uterine disease.
Nervous system: intelligence; evidences of hysteria; hallucinations; sleep; vertigo; gait; station; tendon and muscle jerks; paralysis; tremor; pain ; subjective sensations; convulsions ; headaches and their position.
Eyes: previous attacks of inflammation; injuries; infections; ocular palsy or squint; amblyopia; previous use of glasses; ability to use eyes.
Direct inspection and examination of eyes: inspection of the skull and orbits (symmetry or asymmetry) lids; ciliary borders; puncta lacrymalia; upper and lower cul conjunctivae caruncles; cornea (oblique illumination) ; irides (mobility and color); anterior chambers (depth and character of contents) ; vision; accommodation; balance of external eye muscles ; mobility of globe; tension; light sense; color sense; fields of vision; field of fixation; ophthalmoscope; ophthalmometer; retinoseope; refraction.
Necessarily the examiner will modify the thoroughness of his investigations according to the character of each case.
Direct Inspection of the Eye and its Appendages. The lids should be examined for distended superficial veins, edema, tumors, for example, enlargement of the Meibomian glands, and for anomalies; their edges for inflammation, parasites, misplaced cilia, and small morbid growths; the Puncta for permeability, deviation or retraction from the globe, pressure at the same time being made over the lachrymal sac in order to express from it, through the puncta, any contained fluid ; the caruncles and pliece for swelling, foreign bodies, irritation by incurved cilia, and small morbid growths, for instance, polyps or angiomas; the conjunctival cul de sacs for abnormal secretion, granulations, foreign bodies, concretions and disturbance of the vasecular supply, the examination being carried well up into the upper fornix after thorough eversion of the lid.
In order to evert the lid the patient should rotate the eye strongly downward, while the surgeon seizes gently the central eyelashes of the upper lid between the index finger and thumb of his left hand, and draws the lid downward and away from the globe, placing at the same time the point of thumb of his right hand above the tarsal cartilage of the lid which is to be everted, steadying his remaining fingers upon the patient's brow, and by a quick movement turns the edge of the lid over the point of his thumb, while this is simultaneously depressed. If the patient steadily looks downward during this maneuver there is no difficulty in everting the lid without the aid of the pencil or match stick so commonly employed as a lever.
When there are no lashes on the upper lid the manipulation is more difficult but it can be accomplished by pushing the lower lid beneath the margin the upper in such a manner that it acts as a wedge on which* the superior is. then everted.
The e lower lid is everted readily by placing the tip of the fore finger against the edge of the lid and drawing it downward, at the same time pressing fingers the backward until the lid is turned over it.
The surgeon should also inspect the skin of the face, examine for scars, and investigate the wrinkles in the forehead and between the brows. The supraorbital ridge, the general character of the orbits, and the position and shape of the globes should next be studied. Palpation of the orbit by passing the finger beneath the supraorbital ridge above, along the margin of the malar bone and the superior maxillary below, and to the outer and inner sides, may reveal the presence of accumulations, superficial growths, enlargement of the lachrymal gland, etc. Finally, the action of the orbicularis should be ascertained by causing the patient to close his eyes as if in sleep, and note made of the absence or presence of fibrillary contraction.
When the eyes are opened the length, width, and symmetry of the palpebral fissure and the condition of the commissural angles may be studied (see page 31).
Blood vessels of the Conjunctiva. In health only a few conspicuous blood vessels are to be observed; in inflammation manv more become visible. The conjunctival blood supply may be conveniently disvided, Mr. Nettleship has done into three svstems:
System 1. Posterior conjunctival vessels, whose congestion produces a bright red velvety color, moving, on pressure of the eyelids, with the shifting the conjunctiva, usually associated with muco purulent secretion and indicating conjunctivitis.
System II. Anterior ciliary vessels composed of perforating and nonperforating arteries and veins. The perforating arteries, which supply the sclerotic, iris, and ciliary bodies are the branches seen in health entering about 5 mm. from the corneal margin, their points of entrance, in dark complexioned people, often being distinctly tinted.
The non perforating (episcleral) branches, invisible in the normal eye, produce, when congested, a pink zone surrounding the cornea (‘’ciliary congestion ‘ “circumcorneal zone"), not moving on pressure of the lids with the shifting of the conjunctiva, unassociated with purulent discharge and one indication of iritis.
The perforating veins and their non perforating (episeleral) twigs, when congested, create a zone of dusky hue, often a symptom of glaucoma, or appeal in unequal deep seated patches of lilac or violaceous color, pointing to cyclitis or seleritis.
System III. Anterior conjunctival vessels and the plexus of' capillaries surrounding the cornea, derived from anterior ciliary vessels through whose numerous small branches anastomosis between Systems 1, and 11, takes place. Their congestion produces a circle of bright red injection, often partly on the cornea, a sign of inflammation of this membrane, and typified in the early vascular stages of interstitial keratitis.
In addition to these three varieties of congestion numerous departures are noticeable, making it impossible to specify the individual system involved.
In these types is found a definite local injection, as the leash of vessels passing to a corneal ulcer, or all systems is commingled in a gener.4 inflammation.
Temperature of the Conjunctival Sac. This may be measured with a suitable thermometer having attached to it concavo convex mercury plates which are placed in the lower conjunctival sulcus, or, more accurately, as in physiological experiments, with thermo electric couples. Silex I found the temperature of the lower human conjunctival fold to be 35.55' C. (95.99' F.) i. e. about 2' C. lower than that of the rectum, and in inflamed eyes noted an average increase of 0.98' C. The highest conjunctival temperature is found in acute iritis, but even then does not equal the normal body temperature.
Inspection of the Cornea. This will reveal inflammation, ulceration, opacities, the track of former blood vessels, exudates upon its posterior surface, and foreign bodies. Slight irregularities may be detected by, placing the patient before a window, while his eyes are made to follow the uplifted finger held about a foot from his face and moved in various directions; the image of the window bars reflected from the cornea will be broken as it crosses the spot of inequality. In the same manner abnormalities in the curve of the cornea may be roughly ascertained, because if the curve is normal the reflection does Dot change, at least in the central portion of the cornea; if the curve is abnormal or the surface of the cornea irregular, there is corresponding distortion in the size or shape of the reflection.
A more accurate method is to employ a keratoscope, or Placido's disk, as it is called. This instrument consists of a disk shaped like a target, upon which are drawn concentric black circles, a sight bole being in the center. The patient is placed with his back to the window, while the surgeon holds the instrument 30 cm. in front of the eye, and, looking through the central aperture, observes the reflections of the circles from the cornea. If these are broken or distorted, the indications of irregularity in the surface are present (Fig. 96). Any irregularity on the surface of the cornea is quickly detected by the method of keratometry, especially with the ophthalmometer of Javal and Schiotz (see page 197), the reflections of the targets being greatly distorted as they cross the point of irregularity.
Abrasions and ulcers, even when minute, may be differentiated by dropping into the eye a concentrated alkaline solution ofluorescin (Grublers fluorescin 2 per cent., carbonate of soda 3.5 per cent.), which colors greenishyellow that portion of the cornea deprived of its epithelium, while the healthy epithelium, or even that epithelium which is simply roughened and opaque, as in keratitis, remains unaffected. A minute foreign body may thus be located if situated in the centre of an abrasion, because it appears as a black dot surrounded by a green area. So, also, may the progress of a corneal ulcer be studied, the color test differentiating sharply that portion of the ulceration which is still active from that which is covered with new formed epithelium.
The Width of the Cornea. This may be measured approximately by holding before it a rule marked in millimeters and noting the number of sliaces its width occupies, or, more accurately, by employing Priestley Smith's keratometer. This instrument consists of a scale situated between two plano convex lenses. The Surgeon places his eye at the principal focus of the combination, and, holding the scale before the patient's eye, observes that the cornea subtends on the scale exactly its width (Fig. 97). The average horizontal diameter of the normal cornea is 11.6 mm. (Priestley Smith).
Sensibility of the Cornea. This may be tested by gently touching the surface of this membrane with a wisp of cotton twisted to a fine point. If sensation is intact, the touch will instantly be followed by the reflex action of winking. As a control the opposite eye may be similarly examined. If the cornea is found insensitive, the forehead and face should be examined for areas of anesthesia either with the point of a moderately blunt pin or with an esthesiometer. Thermic as well as tactile sensibility should be investigated.
Oblique Illumination. The surgeon places the patient two feet from the source of illumination and focusses a beam of light with a two inch or three inch lens upon the cornea, at the same time observing the surface tinder examination through a lens of the same focal distance, which acts as a magnifier, held between the thumb and fore finger, the disengaged fingers being utilized to elevate the upper lid (Fig. 98). The distance of the lens must be varied slightly to bring the various tissues the cornea, iris, or crystalline lens within its focus, the patient being required to look up, down, and to either side while the anterior surfaces and media of the eye are illuminated. To detect a foreign body the light should be directed at an acute angle, but if the pole of the lens is to be examined the light should be thrown perpendicularly into the pupil, the surgeon placing his eye in the same direction without interfering with the light. By this method minute abrasions foreign bodies nebulae, and, in short, all corneal changes, may be examined. The character of the aqueous humor, the depth of the anterior chamber, the surface of the iris, synechive, atrophic fibers, small tumors, and persisting pupillary membrane are readily studied, and, finally, opacities in the anterior capsule and axis of the lens can be investigated, and by focussing deeply even the anterior layers of the vitreous. This routine examination should never be omitted.
Recently Dr. Edward Jackson has designed a binocular magnifying lens for examination of the eve by oblique illumination, which is a material aid. Two lenses are placed by side, and so joined that the visual line of the right eye pierces the right lens near its optical center, while the visual line of the left eye pierces the left lens near its optical center. This gives each eye an undistorted field all around the point of fixation, and these fields can be combined in full binocular vision.
In place of this lens a corneal loupe may be employed. This is a lens, properly mounted, by which the cornea is strongly magnified. A corneal microscope, or a specially prepared lens of high power, permits the study of minute changes in this membrane, and is utilized for the examination of traces of former vascularization, and by its help even the circulation of blood in the vessels constituting a pannus may be studied.
The Color of the Iris. Blue and gray are the predominating hues in the irides of the inhabitants of northern countries; brown occurs next in frequency, while the various admixtures produce yellow and green shades. Perfectly black irides are Dever seen, but dark irides, taking the whole population of the world, are the most frequent in occurrence. With rare exceptions the color of the iris of all new born children is of a light grayishblue. The stromal pigment is developed subsequently, and the color of the iris does not become fixed, so to speak, until about the third month.
Slight differences in shade between the two irides are Dot uncommon. More rarely. even in health. the irides differ in color (chromatic asymmetry),
one iris usually corresponds in color with the irides of one parent, and the remaining iris with those of the other parent. Instead of uniform pignientation a single triangular patch or several irregular spots of dark color may appear upon one or both irides (piebald irides). When these spots are small they have sometimes been mistaken for foreign bodies. While chromatic asymmetry is perfectly compatible with health, it is stated to be more com in patients with neuropathic tendencies for example, in cleared and epilepsy. In 25 of 50 cases of chorea of childhood (Sydenbam's chorea examined by the author the irides were equal in color and shade; in the remaining 25 there were slight differences in shade or tone. In only I of these 25 was there any true asymmetry of color. In some instances of chromatic asymmetry there is liability to disease, especially to cataract, on the part of the lighter eye. This susceptibility may be present in several members of the same family.
Discoloration from disease causes one iris to be green, while its fellow remains blue. This indicates iritis or cystitis. It is often an early symptom of inflammation of the iris, and should be looked for in every inflamed eye.
The Pupil. The size of the pupil in health varies with exposure to light and with accommodation and convergence. It is also influenced by age, the color of the iris, and the character of the refraction. Other things being equal, the pupil is generally smaller in old age, in blue eyes, and in eyes with hyperopic refraction, while it is larger in youth, dark eyes, and eyes with myopic refraction. There is no physiological standard on which to base a measurement, but with accommodation at rest the diameter of the pupil varies from 2.44 to 5.82 mm., the average diameter, according to Woinow, being 4.14 min. Under similar illumination the pupils should be round and of equal size, although a large Dumber of measurements for instance, those made among healthy military recruits indicate that slight differences in the width of the pupils are compatible with health.
Measurement of the Pupil. The pupil can be measured approximately by holding before it a rule marked in millimeters and noting the number of spaces its width occupies. The chief objection to this method is, as Edward Jackson points out, that the distance subtended on the rule is less than the diameter of the pupil, in proportion as the distance from the observer's eye is less to the rule than to the pupil. For the purpose of accurate measurement a number of instruments have been devised, known as pupillometers. A simple and useful device is one which consists of a scale of circles held close to the observed eye, the scale being slowly rotated until that circle which matches the pupil in size is reached (Fig. 99). Priestley Smith's keratometer (Fig. 97) can also be employed.
The Pupil reactions and Methods of Testing Them. A uniform light should be employed and the character of the light should be stated. As Turner insists, the light employed for testing the sensitiveness of the retina or visual center should not be more intense than that to which the eye is usually accustomed. Therefore, except under certain circumstances, examinations made by reflecting light into the eye with a mirror or by passing a flame in front of the eye are not accurate. It is much to be regretted that in recorded examinations such loose statements as 11 pupils dilated ... .. pupils contracted," " pupils medium sized," have been so much used.
Mobility of the Iris. The reflex mobility of the pupil 1 is tested to ascertain the presence of attachments between the iris and the lens (synechie), or immobility from atrophy of the iris, or to examine the sensitiveness to light of the retina or visual center.
(a) The patient, placed before a window in diffuse daylight, with one eye carefully excluded, is directed to look into the distance with the exposed eye, which is then shaded, when, in the absence of abnormalities a considerable dilatation of the pupil will occur. On removal of the covering band or card, contraction to the same size as that which existed before the test was applied takes place. This is the direct reflex action of the pupil, and is brought about by a muscular contraction of the sphincter of the iris following the stimulation of the optic nerve.
(b) If during this examination the other pupil, which has been shaded by a card or covering hand, is observed, it will be found acting in unison with its fellow. This is the consensual or indirect reflex action of the pupil. The iris response to light stimulus should also be tested with both eyes open and exposed to the same source of illumination. The eyes should then be covered and exposed alternately and the pupil reactions noted. Under normal conditions the, pupils should be equal, not only with both eyes open, but with one eye shaded.
(c) If the patient is required to look into the distance and then quickly direct his eyes at a near ob ect for example, the point of a pencil held at a distance of about, 10 cm. pupillary contraction occurs under the influence of accommodation and convergence; that is, the sphincter of the iris contracts in association with the ciliary muscle and the internal recti. This is the associated action of the pupils (convergence reaction). Accommodation increases pupillary contraction, but this does not take place under the influence of accommodation unassociated with convergence. It does occur with convergence without the act of accommodation.
(d) A second reflex action of the iris, the other being its contraction under the stimulus of a beam of light (direct light reaction, paragraph a), consists of a dilatation of the pupil when some cutaneous nerve is stimulated, especially one in the skin of the neck. This is the skin reflex (pain reaction), and may be tested by pinching the skin of the neck, or, better, by using a faradic brush.
(e) Finally, the reaction of the iris to the mydriatics and myotics may be tried, especially that produced by cocain, which in the normal eye should cause nearly full mydriasis and widening of the palpebral fissure from stimulation of the sympathetic. (For the physiology of pupil pbenomena see page 96.)
Abnormal Pupillary Reactions, or the Pupil in Disease.' When about to investigate pupil reactions six possibilities, as William McEwen points out, should suggest themselves to the examiner namely, (a) The action of drugs; (b) ocular disease or optical defects; (c) spinal or sympathetic lesions ; (d) localized cerebral lesions in special centers or tracts ; (e) abeyance of brain function ; (f) cerebral irritation. For the convenience of ascertaining in what portion of the path of the pupil reflex the lesion is situated Magnus' has divided it into the following three portions :
1. The Centripetal Part, including the Optic Nerve, Chiasms, Tracts, and Connecting Fibers to the Cortex. If there is interruption of the conducting power of one optic nerve for example .. the right illumination of the pupillary area on that side fails to elicit either the direct or the indirect reflex action of the pupil. On the other band, illumination of the left eye causes its own pupil to contract (direct reflex), as well as the pupil of the right or affected eye (indirect reflex).
Lesions affecting the chiasm and the tract are accompanied by hemianopsia (see page 481) and the special pupillary phenomena which belong to this condition, while lesions in the optical pathway between the corpora quadrigemina and the cortex, although accompanied by probable changes in the visual field, are unassociated with pupillary disturbances.
2. The Part of the Reflex Ring which carries the Light Impulse from the Corpora Quadrigemina to the Oculo motor Nuclei (Meynert's Fibers). If both sides are affected, neither pupil reacts to the impulse of light falling on either eye, but there is normal reaction to accommodation and convergence. (See Argyll Robertson symptom, below.)
3. The Centrifugal Portion of the Reflex Ring (the Nucleus of the Sphincter of the Iris, the Third Nerve, and the Termination of the Third Nerve in the Iris). If the right nucleus is affected, the direct light reflex action of the right pupil is abolished, and also its indirect reflex. Abeam of light directed into the left eye is followed by pupil reaction in that eye (direct reflex). Pupil reaction in that eye also follows light stimulus of the opposite or right eye (indirect reflex), but is somewhat lessened in degree. The pupils react normally to accommodation and convergence, and are unequal, the right being the wider.
If the trunk of the right oculo motor is affected, there is pupillary immobility under the influence of light directed into the right eye, and also when it is directed into the left eye, as well as loss of accommodation upon the right side. Light falling into the left eve produces on this side a normal reaction which is also manifested if the light is directed into the opposite eye. The pupils are unequal, the right being the larger. Similar conditions arise if the peripheral fibers of the oculo motor at their termination in the iris are affected upon one side.
We have now to consider a little more in detail:
1. Dilatation of the Pupil (Mydriasis). This occurs in ocular disease for instance, glaucoma in cases of non conductivity of light (optic nerve atrophy), in orbital disease, and under the influence of raydriatic drugs. It is further seen in fright, emotion, anemia, in depressed nervous tone, neurasthenia, aortic insufficiency, and irri¬tation of the cervical sympathetic. It is noticed in vomiting, forced respiration, and anemia of the brain for example, syncope and is said to be present in persons of low mental development.
In disease of the nervous system dilatation of the pupil, when of cerebral origin, indicates extensive lesion ; when of spinal origin, irritation of the part (McEwen). Systematic writers have divided dilatation of the pupil into irritation mydriasis, caused by irritation of the pupil dilating center or fibers, and paralytic mydriasis, caused by paralysis of the pupil contracting center or fibers, or by failure of the stimulus to be conducted from the retina to the center.The former is apt to be seen in hyperemia and irritation of the cervical portion of the spinal cord, in spinal meningitis, in cases of tumor of the spinal cord, and also, under certain circumstances, in tumor of the cerebral contents, in psychical excitement for example, acute mania and in tabes dorsalis and progressive paralysis of the insane.
The latter, which is also known as iridoplegia, is found in disease at the base of the brain affecting the center of the third nerve, in pressure of the cerebrum when in great amount, as from hemorrhage, tumors, advanced thrombosis of the sinuses, or large abscesses; also in the late stages Of rDeningo encephalitis. It is said to be present in acute dementia when there is edema of the cortex, and is found in cerebral softening Hemorrhage into the centrum ovale and cerebral peduncles also produces mydriasis (McEwen).
2. Contraction of the Pupil (Myosis). This appears in congestion of the iris, paralysis of the sympathetic and also of the fifth nerve, in certain fevers, in plethora, venous obstruction, mitral disease, and under the influence of myotics.
If the myosis is of cerebral origin, it indicates an irritative stage of the affection if of spinal origin, a depression, paralysis, or even destruction of the part (McEwen). Systematic writers divide contraction of the pupil into irritation myosis, caused by irritation of the pupil contracting center or fibers, and paralytic myosis, caused by a paralysis of the pupil dilating center or fibers, or by a combination of both.
Irritation myosis, as just noted, is found in the inflammatory affections of the brain and its meninges e. q. meningitis, abscess (at first the myosis is on same side as lesion), and beginning sinus disease. According to the rule previously given, myosis may change to dilatation if the products of disease become excessive; hence the serious prognostic import of mydriasis under these circumstances. Myosis is seen in the early stages of cerebral tumor, in small hemorrhages into the cerebellum, and at the onset of cerebral apoplexy. Berthold, quoted by Swanzy, uses myosis as a diagnostic symptom between apoplexy and embolism. McEwen points out that the convulsions arising from meningo encephalitis are accompanied by myosis, while those due to epilepsy are usually associated with mydriasis. Apoplexy of, or pressure upon, the pons is associated with myosis.
Paralytic myosis (spinal myosis) occurs in lesions of the cord above the dorsal vertebra. It is especially noteworthy in tabes dorsalis. At first the pupil reacts to light and convergence, but later exhibits the Argyll Robertson phellomenon (or reflex iridoplegia) ; that is, it responds only slightly or not at all to the light impulse, but the associated action of the iris or, in other words, the contraction of the pupil in accommodation and convergence is preserved. The lesion under these circumstances is probably in the fibers which pass from the proximal end of the optic nerve to the oculomotor nuclei. Turner contends that a single lesion in the fore part of the oculo motor nuclei in the Sylvian gray matter is the cause of both myosis and reflex iridoplegia.
Paralytic myosis is also met with in paralysis of the insane, pseudo dementia paralytica of syphilitic origin, bulbar palsy when complicated with progressive muscular atrophy or sclerosis of the brain and spinal cord, and, according to Mills, in some forms of multiple neuritis. The iris reacts peculiarly to mydriatics, which dilate this type of pupil only partially, and their effect is for a long time manifest. Cocain, however, readily expands the small pupil of reflex iridoplegia (Heddoeus). Myotics contract it ad maximum.
Unilateral reflex iridoplegia, or that condition when one pupil is unaffected by varying degrees of illumination of both eyes, but reacts to accommodation, the unaffected pupil responding to separate light stimulus of either eye, may exist with or without mydriasis, and usually is wider than its fellow. It is seen in tabes dorsalis and syphilitic cases. It is probably due to lesion in the sphincter nucleus. It should be distinguished from unilateral reflex blindness (see 7 1, p. 149).
The reverse of the Argyll Robertson symptom has been observed, and indicates disease in a special part of the oculo motor nucleus.
Unequal pupils (anisocoria) are rarely seen in health, although it is stated by one observer (Iwanow) that among 134 healtfiy military recruits the right pupil was larger in 49 and the left in 53, equal width being found in only 12. If there is recent wide dilatation of one pupil and no disease of the eye, the instillation of a mydriatic: may be suspected. Unequal pupils occur in eyes with widely dissimilar refraction if one eye is blind, in aneurysin, dental disease, traumatism, and in diseases of the nervous system. If the disease is cerebral, unequal pupils denote unilateral or focal disease. They are not uncommon in tabes, disseminated sclerosis, and paralytic dementia.
Varying inequality of the pupils, or a mydriasis now occurring on the one side and now on the other, is, according to Von Graefe, a serious premonitory symptom of insanity.
Pupillary Phenomena. The hemiopic p illary inaction is referred to on page 480. The cerebral cortex reflex of the pupil (Haab's reflex) consists of a marked bilateral pupillary contraction which takes place if the patient sits in a darkened room and directs without change of accommodation or convergence his attention to a bright object already present within the compass of the field of vision.
Gifford has described an orbicularis pupillary reaction ; that is, a contraction of the pupil which takes place when a forcible effort is made to close the lids. The discoverer explains this as the result of an overflow stimulus, attempted closure of the lids exciting in the nucleus of the orbicularis fibers of the facial an activity which is transferred to the pupil contracting center. The test is of use in determining whether the pupil sphincter is paralyzed.
Paradoxical Pupil reactions. Dilatation of the pupil under the influence of light stimulus, and contraction when it has been shaded, have been described in cases of meningitis. A good deal of doubt has been cast upon this type of pupil reaction.
Hippus, which is a normal phenomenon for a few seconds after light stimulus to the retina and optic nerve, consists of a rhythmical contraction and dilatation of the pupil occurring without alteration of illumination or fixation. It is seen in cerebrospinal sclerosis, disseminated sclerosis, neurasthenia, hysteria, psychical disturbances, epilepsy, and acute meningitis in its early stages!
Testing Acuteness of Vision. For the purpose of determining acuity of sight test tvpes are employed, in which the letters are of various sizes and are constructed according to the methods described on page 138.
Inasmuch as manv good eyes possess a vision of five fourths of the standard angle, Dr. James Wallace of Philadelphia and. Dr. Culver of Albany have arranged a series of test types in which, instead of an angle of five minutes, one of four minutes has been substituted as tile basis of each letter.
Dr. Randall points out that the order of the letters should be adjusted so as to bring the confusion letters in the same alternation. It is preferable to have large letters at the top of the card, no particular advantage accruing from the inverted arrangement. The color of the card is of importance, a cream color verging on the India tint giving the best definition through lessening of irradiation (Randall). White letters on a black background are also employed.
When ft is desired to test the acuity of sight, the patient is placed 6 meters from the type card, in a well lighted room, and each eye is tried separately. If the letters of No. 6 (20 feet, approximately) are read, vision is normal or 1, but if at the same distance no smaller letters than those numbered 18 (60 feet) can be discerned, vision is 1/3. It is usual to express these results according to the formula, V= d/D, in which V stands for visual acuteness, d for the distance at which the type should be read, so that in these instances the vision would be recorded 6/6 and 6/18, or in feet 20/XX, 20/LX (see also page 140).
Any other distance may be chosen, provided it does not place the patient closer to the test card than 3 meters, at which close range the function of accommodation would introduce an element of inaccuracy. Thus, the scale made use of by De Weeker and elaborated by Oliver assumes 5/5 (15/XV, approximately), instead of 6/6 as 1/1. In like manner, a 4 meter distance may be utilized, as has been done by Edward Jackson. Rays coming from letters at 6, 5, or 4 m. have so little divergence when they reach the eye that they are usually considered parallel; hence if the patient sees distinctly at this distance, his vision is perfect at the longest range. In point of fact, however, as Frederick K. Smith has insisted, there is an appreciable divergence of rays from the distances mentioned, equivalent respectively to 1/6, 1/5 and 1/4 and 1/4 diopter lens. In the final adjustment of glasses this divergence should be recognized.
For the purpose of a control test, and also for determining the visual acuity of illiterate persons, cards are employed on which a number of black dots and disks of various sizes are placed, which should be counted at different distances. Among the best known of these are Burchardt's " international tests." For the same reason Edward Jackson has designed a visual test which is an incomplete square, the incomplete side being turned successively in different directions (see also page 140). A useful test for children may be constructed by printing on a card small pictures of wellknown objects which in size shall approximately conform to the standard angle. Such a series has been published by Dr. Wolffberg of Breslau.
If the patient fails to decipher the largest letter at the distance employed, be should be moved closer to the card. Thus, he may be unable to read the type numbered 60 at 6 m., but may discern this at 4 m., v= 4/60 or 1/15 of normal. Still further depreciation of visual acuity is recorded by requiring the subject to count the outstretched fingers at various distances (I/2, I or 2 m.), V = counting fingers at the distance measured. When the ability to distinguish form (qualitative light perception) no longer exists, the perception of light should be tried by alternately screening and shading the eye, or by illuminating the eye with light reflected from a mirror or focussed through a magnifier.
Light sense. Having determined the acuity of vision by means of the test letters, the examiner has ascertained the form sense, and may proceed to investigate a second subdivision of the sense of sight, the light sense, which is the power possessed by the retina, or center of vision, of appreciating variations in the intensity of the source of illumination. An instrument called a photometer is employed for this purpose, and consists essentially of an apparatus by which the intensity of two sources, of light may be compared as, for example, in the apparatus of Izard and Chibret. The patient, looking into the instrument, sees two equally bright disks. One disk is now made darker, and the power of the eye to perceive the difference in the illumination of the two disks is ascertained ; or one disk is made entirely dark and then gradually illuminated, and the smallest degree of light noted by which the patient can perceive the disk coming from the darkness. The former is called light difference (L. D.), and the latter light minimum (L. M.).
Other instruments have been invented by Forster, Landolt, and R. Wal lace Henry! By means of Forster's photometer (Fig. 100) the lowest limit of illumination with which an object is still visible (the minimum stimulus) is ascertained. The following description is taken from Fuchs :
" A box, A, blackened on the inside, bears on it , anterior wall two apertures for the two eyes, a, a, which look through these apertures at a plate T which is fastened upon the posterior wall, and upon which large black stripes upon a white ground are placed as test objects. The illumination is produced by a candle of one candle power, L, the light from which falls through a window, F, into the interior of the box. In order to make the illumination perfectly uniform, the window is covered with paper which is made translucent by impregnating it with fat. By a screw, 8, the size of the window can be altered from complete closure up to an aperture of 5 square cm. The patient is made to look into the apparatus with the window closed, and the plate therefore unilluminated. Then the window is slowly opened until the stripes upon the plate can be recognized. The size of the opening requisite for this purpose gives a measure of the light sense of the person examined. In conducting this examination the precaution must be adopted of making the patient stay beforehand in the darkness."
Some information in regard to the light sense may be obtained by testing the acuity of vision on two cards under a different degree of illumination, and by comparing the results with a similar examination of a subject believed to have normal power of appreciating different degrees of illumination. The patient with normal light sense will be able to recognize the printed letters when the patient with defective light sense is unable to read them. It is very important in many cases, especially of slight retinal change, to ascertain the acuity of sight under full and under diminished illumination.
Color sense. A third subdivision of the sense of sight is the colorsense, or the power which the retina has of perceiving color, or That sensation which results from the impression of light waves having a certain refrangibility. This examination is of especial interest in the detection of colorblindness (see page 603).
Measurement of the Vision for Colors. Various methods are employed for ascertaining the qualitative and quantitative vision for colors. Direct vision for colors may be studied by placing the patient at a given distance for example, 5 m. frorn a chart or disk of graduated colors. In the scale of De Weaker and Masselon the colored surface, 2 cm. square, should be recognized at 5 m. ; that is, the chromatic vision V C or C = 1; if a colored test must be four times this size in order to be recognized, C = 1/4 etc. (True and Valude). Charles A. Oliver has designed a convenient apparatus for measuring the color sense in this manner at a given distance, and has found that red requires 2 2/3mm. of surface exposure to be properly recognized by the normal eye at 5 m. distance; yellow, a slightly increased area ; blue, 8 3/4 mm.; green, 10 3/4 mm. ; and violet '22 3/4 mm.
Selection Tests. Usually one or other of the methods which consist essentially in testing the power to match colors conveniently used in the form of colored yarns is employed. Practically, all of these tests are modifications of Holmgren's wools, a specially commendable method being that devised by Dr. William Thomson. (For the full consideration of these tests consult page 603.)
Special Tests. In order to obviate the change which occurs in the color of yarns, etc. the color sense may be investigated by the Spectroscope, which, however, is not convenient for office work. The changeable colors, which are colored mixtures like those of wools, may be produced by passing polarized light through a quartz plate and again through a Nicol prism.
The following account, condensed from Carl Weiland's' description of the Javal ophtbalmometer as a chromatameter, gives the essential points of instruments constructed for this purpose, and of his own happy modification of the ophthalmometer:
In the color measurer of Rose the light is passed through a Nicol prism first, and then by a diaphragm through a double refracting prism, from where it enters first a quartz plate cut at right angles to its optic axis, and finally a second Nicol prism, Two circles of complementary colors are thus produced, which change continually when the up er quartz and Nicol prism are rotated, but always remain complementary to each otg. Konig's ophthalmo leukoscope is like Rose's instrument, except that the first Nicol prism is wanting and that quartz plates of different thickness 5, 10, or 15 mm. are used, according to the degree of color saturation required.
In Chibret's chromato photo optometer the quartz plate is cut parallel to its optic axis, and the change in colors is obtained by inclining the plate at different angles to the line of vision. As these instruments are expensive, Weiland has devised a chromatometer which he describes as follows:
The color attachment to Javal's keratometer consists " of a straight metal tube, about 1 1/2 inches in diameter, reaching from the place where the patient's cornea usually is to about the beginning of the barrel of the telescope, and so fastened to the head rest that its axis coincides with the axis of the instrument. At the front part of this colortube there is a plane glass plate behind which a Nicol prism is fastened in a cork. From this prism the polarized light passes by a round diaphragm through a quartz plate, cut at right angles to its axis and about 5 rum. thick.
" The patient, looking with the Javal through this tube, will see two large colorfields partially overlapping each other. These color fields are of complementary hues, while the place of overlapping shows white; provided, of course, that white light as reflected from a white surface, like a piece of white paper, is employed in this experiment. If now the are of Javal be rotated, while the color tube remains in the same position, the colors will change continually, but always remain complementary, returning, however, to their original hues after the are has been rotated through 90'.
" For the purpose of examination, place the patient's eye at the ocular of the instrument, after you have first looked in yourself and given to the new color tube such a position that blue and yellow appear, because thus most color blind persons will recognize two different color;. Now ask the patient whether the two colors are exactly alike or at least shades of the same color. If he answers No, turn the barrel of the Javal slowly through 90', telling the patient to stop you as soon as the two colors are the same. If he has good color sense he will always see two different colors, but if he is color blind, he will find that in a certain position of the are the two colors will appear alike, or at least as much alike as if they were shades of the same color. These colors will usually be green and rose for a green blind person, while the red blind person generally selects a more bluish green and a rose with much more red in it. This suffices to prove that the case is color blind."
Pseudo isochromatic Tests. According to Mauthner, certain colors which the normal eye differentiates appear to the color blind person " falsely of the same color" i. e. pseudo isochromatic. At one time the color blind subject will describe as alike a row of colors which are not so ; at another time, when the test relates to the recognition of letters or signs on a colored ground, be will Dot see them, especially when the color of the ground and the letters (figures, signs, etc.) are pseudo isochromatic and equally clear.
Daae has placed upon a card on which are fastened ten horizontal rows of variously colored wools one row which contains only red wools, one which contains only green, and one which contains only purple. In the other seven rows the various colors are placed next to each other. The color blind person designates rows as of the same color when this is Dot the case and the reverse. A test of this character, according to Mauthner, is a positive pseudo isochromatic test, because it depends upon the positive expressions of the patient in regard to color similarity.
the negative pseudo isochromatic tests negative because, according to Mauthner, they depend upon the fact that the color blind person does not read figures or letters which are drawn upon a pseudo isochromatic groundthe plates of Stilling may be mentioned (see page 604). Pseudo isochromatic powders have also been prepared by Mauthner for the same purpose.
Simultaneous contrast tests based upon experiments with colored shadows are not satisfactory in practical work. Meyer's discovery that if a gray ring or border is placed upon a colored for example, red piece of paper, and then covered with tissue paper, it will appear to the normal eye in the complementary color that is, green has been utilized for practical work, particularly in the letters devised by Pffliger. These consist of black or gray letters upon a colored ground. The letters are then covered by tissue paper and appear in the complementary color.
Lantern tests are sometimes employed, and are of great value in the examination of railroad employ'es (see page 604).
Accommodation is measured in practical work by finding the nearest point at which fine print can be clearly deciphered. The types most frequently adopted are those known as Snellen's 0.5 or Jaeger's 1. Frequently, however, the types in common use are very badly printed and constructed. The letters should be so arranged that they subtend the standard angle of five minutes at a given distance; for example, 25 cm., 50 cm., etc. Ordinarily, these letters are arranged upon suitable cards. Excellent series have been published by Schweigger, by James Wallace, and by Charles A. Oliver.
In order to study the phenomena of accommodation the student should record (l) The Dearest point of perfectly distinct vision attainable with the smallest readable type, or the punctum proximum (abbreviated p. p, or simply p). (2) The far point of distinct vision, or the punctum remotum (abbreviated p. r, or simply r). (3) The range, amplitude of accommodation, or the expression of the amount of accommodative effort of which the eye is capable. This is expressed in the number of that convex lens placed close to the cornea whose focal length equals the distance from the near point to the cornea, and which gives rays a direction as if they bad come from the far point; thus, if the near point be at 10 cm., the lens which expresses the amplitude of accommodation is + 10 D. 100/10. A convenient measure is a stick marked on one side in inches and fractions of an inch, on the other side in millimeters and centimeters ; on the edge the amplitude of accommodation is expressed in diopters. (4) The region or the space in which the range of accommodation is available. (5) Relative accommodation, or that independent portion of this function which can be exercised without alteration in a given amount of convergence, and is divided into a negative portion, or that portion which is already in use, and a Positive portion, or that portion which is not in use. If the patient is unable to read the fine test print at any distance, a convex lens should be placed before the eye and the near point and far point recorded with its aid (see also page 134).
Mobility of the Uyes. This is tested by causing the. patient to follow with his eyes, the head remaining stationary, the movements of the uplifted finger, which is directed to the right, to the left, upward, and downward. Both eyes must be observed, and note made of any lagging in their movements or of the failure of either eye to turn into the nasal or temporal canthus. At the same time, the relation of the movements of the upper lid to those of the eyeball is recorded. The attention of the patient must be centered upon the moving finger, and allowance should be made for the imperfect mobility of highly myopic eyes. Any asymmetry of the skull, or difference in the level of the two orbital margins, may be observed, because such conditions are not infrequently associated with ametropic eyes, especially when the two eyes possess great inequality in refractive conditions.
Investigation of the Balance of the External Eye muscles.Under normal conditions perfect equilibrium of the external eye muscles is present, but preponderance, for example, of the power of the external recti, or vice versa produces a tendency to divergence or convergence, which, however, is overcome, with the preservation of binocular single vision, in spite of the disturbed equipoise. This condition was named by Von Graefe dynamic strabismus. It is frequently designated insufficiency of the ocular muscles. Disturbance of the normal balance (imbalance, as it is now called) creates a tendency for the visual lines to depart from parallelism, or the various phorias of G. T. Stevens's classification. In order to ascertain the condition of the ocular muscles, in so far as their balance is concerned, we may employ the following tests:
(1) Approach the finger to within a few inches of the eyes which are, steadily fixed upon its tip, and note if a convergence to a distance of 8 cm. (3 1/2 in.) is attainable. If one eye deviates outward before this point is reached, weakness of the interni is present, the eye possessing the weaker internus usually being the one which exhibits the deviation. This test is a rough one, and valuable chiefly for ascertaining which of the interni is the weaker.
(2) Require the patient to fix upon a fine object, as a pin point, held below the horizontal, 20 or 25 cm. from the eye, and, in order to remove the control of binocular vision, cover one eye with a card or the band, and observe whether the eye under cover deviates inward or outward, and returns to fixation when the cover is removed. If the patient fixes the object accurately, and the manipulations of covering and uncovering first one eye, and then the other, are rapidly performed, trustworthy results will be obtained. In general terms, each millimeter of movement of the deviating eye corresponds to 2' of insufficiency as measured by prisms. In the case of the interni, if the covered eve moves in to fix, with several distinct impulses, each impulse should be mt~ltiplied into the foregoing result (Randall).
(3) Produce vertical diplopia with a prism, and test the functions of the lateral muscles at a distance of 6 m.
A small flame is placed against a dark background at 6 m. from the patient and on a level with his eyes. In an accurately adjusted trial frame a prism of 7' is inserted, base down, before one eye for example, the right. Vertical diplopia is induced, and the upper image belongs to the right eye. If the flames stand one directly over the other, there is no inclination to divergence or convergence. If the upper image stands to the left, there is weakness of the interni ; if to the. right, of the externi. That prism placed with its base in or out before the left eye, according to circumstances, which brings the two images into a vertical line, measures the degree of the deviation.
Thus the presence or absence of lateral insufficiency is determined.
(4) Produce lateral diplopia and test the functions of the vertical muscles at a distance of 6m.
The patient is seated as before, and a prism of sufficient strength to induce homonymous diplopia is placed before one eye for example, the right i. e. with its base toward the Dose. If the images are on the same level, no deviating tendency is present. If the right image rises higher than the other, the visual line of the right eye tends to be lower than that of its fellow, and there is insufficiency of the vertical muscles. That prism, placed with its base down before the left eye, which restores the images to the horizontal level measures the degree of deviation.
(5) Produce vertical diplopia, and test the functions of the lateral muscles at the ordinary working distance, or 30 cm. For this purpose it is customary to employ the equilibrium test of Von Graefe, in which a card, having upon it a large dot through which a fine line is drawn, is held 25 or 30 cm. from the eyes, diplopia being induced by means of a prism of 10' or 15', base up or down, before one eye. A more accurate test object is a small dot and fine line, or a single word printed in fine type, requiring accurate fixation and a sustained effort of accommodation. If, the prism being placed base down before the right eye, the images stand exactly one above the other, equilibrium is evident; if the tipper image (image of the right eye) stands to the left of the lower image, there is crossed lateral deviation, and that prism, placed before the left eye with its base toward the nose, which restores the image to a vertical line measures the tendency to divergence, exophoria, or insufficiency of the internal recti. If the upper image stands to the right of the lower, there is homonymous lateral deviation; and the prism placed before the left eye, with its base toward the temple, which restores the images to a vertical line, measures the tendency to convergence, esophoria, or insufficiency of the external recti.
(6) Ascertain the power of adduction (prism convergence), abduction (prism divergence), and sursumduction (sursumvergence) by finding the strongest prism which the lateral and vertical muscles can overcome.'
Beginning with adduction, find the strongest prism placed before one eye, with its base toward the temple, through which the flame still remains single. The test should begin with a weak prism, the strength of which is gradually increased until the limit is ascertained. This varies from 30' to 50'. In this test, if diplopia occurs when, for example, the strength of the prism been reduced 20', single vision may not return until the prism has been reduced, for instance, to 10'. The space between the greatest and least power of adduction has been described as the 11 region of diplopia" (Reeves, Lippincott, Gould).
In like manner abduction is tested, the prism now being turned with its base toward the nose; 6" to 8' of prism should be overcome. The ratio between adduction and abduction should be 6 to I (Stevens) i. e. if adduction is 48", abduction should be 8', but, according to Risley, in carefully corrected or emmetropic eyes the ratio is 3 to 1.
Sursumduction, or the power of uniting the image of the candle flame seen through a prism placed with its base downward before one eye with the image of the same object as seen by the other eye, is ascertained by beginning the trial with a weak prism I'/2 or I' and gradually increasing its strength.
The limit is usually 3', but may be as high as 8' or 10'.
If the eyes of the patient under examination are ametropic, the proper correcting lenses should be placed before them, and the examination for the various forms of insufficiency made through this glass. It is, moreover, exceedingly important that the correcting glass should be accurately centered; otherwise, in a lens of considerable thickness, a prismatic effect, would be produced which would utterly preclude accurate determination of the muscular conditions, especially of the vertical muscles, where the search for fractions of a degree of deviation is sometimes necessary. If the muscular examinations have been undertaken as part of a routine preliminary investigation of an eye, they should be repeated after the refraction has been accurately determined, and, if anomalous, corrected.
Practically, all of the examinations for muscular errors can be made with a series of prisms and a trial frame, but they are facilitated by the use of certain instruments of precision, especially some form of Herschel or re volving prism, the one devised by Risley being the best (Fig. 101). The latter consists of two prisms, superimposed with their bases in opposite directions, constituting a total value of 45'. They are mounted in a cell which has a delicately milled edge, and fits in the ordinary trial frame. The milled edge permits convenient turning in the frame, so that the base or apex of the prisms can be readily placed in any desired direction. The prisms are caused to rotate in opposite directions by means of a milled screw head projecting from the front of the cell. With this rotary prism the strength of the abducting, adducting, and supra and infraducting muscles can be measured. If the rotary prism is placed before the left eye with the zero mark vertical, and the screw turned to the right or left, it will cause the base of the resulting prism to be neither inward or outward, that is, toward the nose or temple, as may desired; or it may be placed with the zero marked horizontal and the base turned upward or downward. All examinations for muscular defects may be accurately ascertained with Dr. G. T. Stevens's well known phoro.mfter, which is illustrated in Fig. 102.
One of the simplest tests of the ocular muscles is the obtuse angled Prism of Maddox. This is composed of "two weak prisms of 30, united by their bases. On looking through the line thus formed at a distant plane, two false images of it are seen, one higher and one lower than the real image seen by the other eve, the position of which, to the right or the left of ihe line between the false image, ,, indicates the equilibrium of the eye. A faint band of light, of the same breadth as the two false images, is seen extended between them" (Fig. 103). The answers of the patient may be materially assisted by placing a red glass before one eye and thus tinting the real image. If this stands directly in the center between the two false images, all forms of insufficiency are eliminated; if it stands to the right or to the left, there is insufficiency of the external or of the internal recti ; if it stands above or below the center, or is fused with the upper or the lower image, there is insufficiency of the superior or inferior recti.
Insufficiency of the oblique muscles (cyclophoria), according to Savage, may be detected "by placing a Maddox prism, with its axis vertical, before one eve (the other being covered), which regards a horizontal line on a card 18 in. distant. This line appears to be two, each parallel with the other. The other eve is now uncovered, and a third line is seen between the other two, with which it should be parallel. Want of harmony in the oblique muscles is shown by want of parallelism of the middle with the other two lines, the right end of the middle line pointing toward the bottom and the left end toward the top line, or vice versa, depending upon the nature of the individual case"' (Fig. 104).
The rod test, also designed by Maddox, depends upon the property of transparent cylinders to cause apparent elongation of an object viewed through them, so that a point of light becomes a line of light so dissimilar from the test light that the images are not united. It may be suitably employed by having mounted in a cell which will fit in the trial frame a transparent glass rod colored red 3/4 in. long, and about the thickness of the ordinary stirring rod used by chemists, or a series of glass rods placed one above the other (Fig. 105).
The examination for horizontal deviation is thus described : " Seat the patient at 6 m. from a small flame, placed against a dark background, and put the rod horizontally be ore one eye. If the line passes through the flame, there is orthophoria (equipoise) as far as the horizontal movements of the eves are concerned. Should the line lie to either side of the flame, as in most people it will, there is either latent convergence or latent divergence; the former, if the line is on the same side as the rod (homonymous diplopia) ; the latter, if to the other side (crossed diplopia) " (Fig. 106).
In order to test the vertical deviation, the rod is placed vertically before the eye: a horizontal line of light appears, and the patient is asked if the line passes directly through the flame or if it appears above or below it. Tile following rule, quoted from Maddox, will suffice to indicate the 11 hyper eye : " If the flame is lowest, there is a tendency to upward deviation of the naked eye ; if the line is lowest, of the eye before which the rod is placed" 1 (Fig. 107).
The measurement of the extent of the deviation may be made in the ordinary way by finding that prism, placed before the naked eye (preferably with the rotary prism of Risley), which brings the line and flame together.
In order to avoid the awkwardness of the phraseology 11 insufficiency of the internal recti," etc., and at the same time more accurately to describe the muscular anomalies, the following terminology has been introduced by Dr. George T. Stevens, and has received a deservedly wide acceptation :
The condition in which all adjustments are made by muscles in a state of physiological equilibrium is called orthophoria.
Disturbances of equilibrium are known as heterophoria, or insufficiencies of the ocular muscles.
The deviating tendencies of beterophoria may exist in as many directions as there are forces to induce irregular tensions.
The following system of terms is applied to the various tendencies of the visual lines:
1. GENERIC TERMs. Orthaphoria: A tending of the visual lines in parallelism.
Heterophoria: A tending of these lines in some other way.
11. SPECIFiC TERms. Heterophoria may be divided into
1. Esophoria: A tending of the visual lines inward;
2. Exophoria: A tending of the lines outward;
3. Hyperphoria (right or left): A tending of the right or left visual line in a direction above its fellow.
This term does not imply that the line to which it is referred is too high, but that it is higher than the other, without indicating which may be at fault.
III. COMPOUND TERMS. Tendencies in oblique directions may be expressed as hyperesophoria, a tending upward and inward; or hyperexaphoria, a tending upward and outward. The designation “right" or “left" must be applied to these terms.
Power of Convergence. In order to determine the maximum of convergence an instrument known as an ophthalmo dynamometer may be employed. The one devised by Landolt consists of a metallic cylinder, blackened on the outside, placed over a candle flame. The cylinder contains a vertical slit 0.3 mm. wide, covered by ground glass. The luminous vertical line thus produced is the object of fixation. Beneath the cylinder is attached a tape measure graduated on one side in centimeters, and on the other in the corresponding number of meter angles. The fixation object is gradually approached in the median line toward the patient, until that point where double vision occurs is reached, or the Dearest point (punctum proximum) of convergence, and the distance in centimeters read from one side of the tape, and the corresponding maximum of convergence in meter angles on the other.
The minimum of convergence may also be ascertained with the instrument, but when this is negative it is determined by finding the strongest abducting prism which will not cause diplopia while the patient is fixing a candle flame at 6 m. If the number of the prism is divided by 7, the quotient will approximately give in meter angles the amount of deviation of each eye when the prism is placed before one. The amplitude of convergpnee is equivalent to the difference between the maximum and minimum of convergence.'
The Field of Vision. When the, visual axis of one eve is directed to a stationary point, Dot only is the object thus " fixed" visible, but all other objects contained within a given space, which is large or small in proportion to the distance of the fixation point from the eye. This space is the field of vision (conveniently abbreviated V. F.), and the objects within it imprint their images upon the peripheral portions of the retina, or those which are independent of the macula lutea. In contradistinction to visual acuity and refraction, which pertain to the macula in the act of direct vision, the function of sight capable of being performed by the Test of the retina is called indirect vision.
The limits of the visual field may be roughly ascertained in the following manner: Place the patient with his back to the source of light, and have him fix the eye under examination, the other being covered, upon the center of the face of the observer, or upon the eve of the observer, which is directly opposite his own at a distance of 2 ft. Then let the surgeon move his fingers in various directions midway between himself and the patient on a plane with his own face, until the limits of indirect vision are determined, controlling at the same time the extent and direction of the movements by his own field of vision. Instead of using fingers as the test object, the author, in common with many surgeons, is accustomed to employ a black rod 18 in. long, which is capped with an ivory ball 12 mm. in diameter. Colored balls may also be employed in the same way, and a fair idea of indirect color vision obtained.
These methods suffice to discover any considerable limitation of the visual field, but should always be supplemented by a more exact procedure.
If it is desired to have a map of the field not larger than 45' in extent, let the patient be placed 25 cm. from a blackboard, which may be conveniently ruled in squares, and fix the eye under observation upon a small white mark. The observer then moves the test object, a piece of white paper I cm. square, affixed to a black handle, from the periphery toward fixation, until the object is seen. If eight peripheral points are marked and afterward joined by a line, a fair map of the field of vision will be obtained,' which may be transcribed upon a chart, like the one originally suggested by Joy Jeffries (Fig. 108).
In like manner a campimeter may be employed, the one designed by De Wecker being a useful model. It may be understood by reference to Fig. 109. The patient's eye regards tile cross in the center of a black vertical table while the test object is moved from the periphery toward the center, and the outermost limit of its recognition is marked on the radiating line which it follows. When each line has thus been traversed, the points are joined by a continuous line, and a graphic representation of the visual field results.
field of vision may also be examined on a flat, surface at a greater distance than 25 to 30 cm., after the manner proposed by Bjerrum. The examinations are made at a distance of 2 m. oil a large black screen 2 m. in breadth, which can be let down from the ceiling to the floor. At this distance the blind spot (see p. 169), instead of measuring about 2 1/2 cm., as on an ordinary perimeter, measures 20 cm. in diameter, and everything else is in the same proportion. The test objects used by Bjerrurn are small circular disks of ivory fixed on the ends of long dull black rods. They vary from 10 to I mm. in diameter. The examination is begun in the ordinary way at 30 cm. with the 1 10 mm. disk, and then continued at 2 meters' distance with a 3 mm. disk. In the first case the visual angle approximately is 20, and in the second 5'. The normal boundaries in the first instance have been given; in the second they are 35' outward, 30' inward, 280 downward, and 25' upward. The method is valuable for finding sector shaped defects, irregular limitations, and especially scotomata (see p. 169).'
Beyond 45' measurements on a flat surface cease to be accurate, because the object is too far away from the eye; rays perpendicular to the visual line coming from a peripheral object would be parallel to the blackboard, and could not arise from it or any object passed across its surface.
The accurate investigation of the functions of the periphery of the retina requires the use of an instrument called a perimeter, for which we are chiefly indebted to Aubert and Forster. This instrument consists essentially of an are (or a semicircle) of wood or metal marked in degrees which rotates around a central pivot, which at the same time is the fixing point of the patient's eye, placed 30 cm. distant i. e. at the center of curvature of the perimeter are. The test object, I or 1 1 cm. in diameter, affixed upon a carrier, is moved from without inward along the are, and the point noted in each meridian at intervals of 30', where it is recognized. Usually the examination is begun with the arc in the horizontal position, which is then moved from this meridian to the next (e. g. up and out), and so on until the whole field has been investigated. Generally it is sufficient to examine eight meridians (Fig. 110).
The result is transcribed upon a chart, prepared by having ruled upon it radial lines to correspond to the various positions of the arc, and concentric circles to note the degrees.
The numbering of the meridians on the numerous charts which have been published is far from uniform, as may be ing diagrams (Figs. 111, 112,113). Noyes and Knapp,' in order to secure uniform records of the visual field, have advised the designation of the meridians according to the method employed by Helmboltz in his study of the movements of the eye viz. "to take as the zero point the left end of the horizontal meridian of each eye, and to count from left to right as the hands of a watch viewed by a person under examination move. O~ accordingly marks the temporal end of the horizontal meridian of the left and the nasal end of the same meridian of the right eye; 180' marks the nasal end of the horizontal meridian of the left and the temporal end of the same meridian of the right eye." I
Since the Aubert Fiirster instruments appeared the perimeter has undergone numerous modifications and the market is supplied with a host of models. The most practical and time saving instruments are the so called self registering perimeters, especially those designed by Stevens, McHardy, and Priestley Smith. A useful model for bedside examinations is the hand perimeter of Schweigger.
The size of the visual feld varies considerably within normal limits, being influenced by the character of the light, which should illuminate with equal intensity all portions of the perimeter are in each position; by the size of the test object, which should be not less than I and not greater than 2 cm. in width; by the attention of the patient, whose eye should accurately regard fixation during the measurement; and by the patient's physical and mental condition. Undue prolongation of the examination produces retinal tire and corresponding contraction of the visual field. The extent of the field of vision is also somewhat under the influence of the size of the pupil and the state of refraction, being larger in eyes with widely dilated pupils or with hyperopic refraction, and smaller in eyes with contracted pupils or with myopic refraction. Enlargement of the visual field may be noted during accommodation for the near point and when the patient wears concave glasses 1 (Mauthner).
The average physiological limits of the form field, or, what is practically the same thing, the field when this has been measured with a square of white 11 cm. in width, are outward, 90' ; outward and upward, 70'; upward, 50'; upward and inward, 55' ; inward, 60' ; inward and downward, 55'; downward, 72'; downward and outward, 850.
These limits, which form a good working field, are somewhat exceeded by the mean limits resulting from the examination of a number of normal eyes, as recorded by Forster, Landolt, and Baas.' The last named author finds the average result of ten observers as follows: Outward, 99'; upward, 65' ; inward, 63' ; downward, 76'. Figures indicating a "minimal field," or "smallest physiological field," have been recorded, varying from 90' (Forster) to 50' (Treitel) outward; 55 21' upward; 60 40' inward; 70 40' downward. Certainly, in the judgment of the author, the smaller of these limits cannot be regarded as physiological, and the greater is about equal to the average working field already given.
As we ordinarily measure the visual field, the measurement represents the relative visual field, in contradistinction, as Baas points out, to the absolute visual field. The former records the limits for a test object of definite size; the latter the maximal expansion which it is possible to obtain. The figures then given are the relative visual field (test object 1 2 cm.), and transscribed upon a chart produce Fig. 114.
Examination of this chart shows that the field of vision is not circular, being greatest outward and below, and most restricted inward and above. This restriction depends partly upon anatomical reasons i. e. the edge of the orbit, the lids, and the nose interfere with vision, and partly upon physiological reasons i. e. the percipient layers of the retina extend farther forward on the nasal than on the temporal side, or, as Landolt expresses it, the outer part of the retina is less used than the inner, and its functions, therefore, are less developed. Hence, as each portion of the field corresponds to the opposite portion of the retina, the inner part is smaller than the outer. To avoid the influence of the physical obstacles afforded by the cranial bones, the eye should be made to fix an object in each meridian 30’ in the direction opposite to that under measurement or else suitable rotation of the head should be made.
Binocular Field of Vision. The field of vision for each eye having been defined, it remains to point out that the field of vision which pertains to the two eyes, or that portion in which binocular vision is possible, constitutes only the area where the central and inner parts overlap. This is evident from the diagram. The continuous line L bounds the field of vision of the left eye, and the dotted line R the visual field of the right eye. The central white area corresponds to the portion common to both eyes, or to that area in which all objects are seen at the same time with both eyes; the shaded areas correspond to the portions in which binocular vision is wanting. In the middle of the white area lies the fixation point,f, and on each side of it the blind spots of the right and left eye, r and I (Fig. 115).
Having thus determined the limits and continuity of the visual field, the functions of the peripheral parts of the retina in regard to perception of colors, acuity of vision, and appreciation of light should be investigated.
Color field. The color field is examined in the manner described in connection with the general visual field, the squares of white in the instrument being replaced by pieces of colored paper 1 to 2 cm. in diameter. The order in which the colors are recognized from without inward is (1) blue, (2) yellow, (3) orange, (4) red, (5) green, (6) violet. In practical work blue, red, and green are the colors employed. Nonsaturated colors are not correctly recognized when the test object is first seen. Thus, yellow at first appears white; orange, yellow; red, brown; green, white, gray, or gray blue; and violet, blue. The investigation of this zone of imperfect color perception is important in various pathological conditions, especially in the study of the visual fields of hysteria and of disseminated sclerosis.
The physiological extent of the color fields, like that of the general field, is subject to variations within normal limits, which are represented by the figures in the following columns. In each left hand column are the figures denoting the extent of an average color field mapped with 1 cm. square testobject, while in each right hand column are the averages of the results of ten observers recorded by Baas, the size of the test object being 20 mm. in diameter:
These when transcribed UDon a chart, are represented in Fig. 116
As may have been inferred, the extent of the color field is greatly governed by the size of the test object. According to Gowers,' who has recently reopened this subject, with a sufficiently large area of color it will be found that all the color fields differ in extent very little from the fields for white. Green alone seems to fall short of the edge of the white field by about 5'. The extent of the color field is further governed by the character of the light, the nature and saturation of the color, the contrast in luminous intensity between the colored test object and the background. To quote from Ward Holden: Other conditions being the same, the field becomes larger as the saturation, the intensity, or the size of the color is increased; and the field is larger the less the contrast in luminous intensity between test object and background.
The Acuity of Vision of the Peripheral Parts of the Retina.This diminishes from the macula to the periphery. It may be tested with small squares of black paper, separated from each other by their own width, by noting the point in each meridian where they are recognized as separate objects. The tests of Landolt and Ito are 6, 5, 3, and 2 mm. black quadrants on a white ground. Groenouw employs as a test object to be passed along the perimeter are black points on a white ground of I/4, ½, 1, 2, and 4 mm. in diameter. The result obtained is called “visual acuteness for a point." 2 The results have the form of a horizontal oval nearly parallel to the limits of the visual field.
The Light sense of the Periphery of the Retina. This may be tested conveniently with Ward Holden's tests, which are thus described by the author: One card has a I mm. black point on one side, and a 1 5 mm. quadrant of light gray, having AL of the intensity of white, on the other. With a perimeter of 30 cm. radius the black point and gray patch are each seen by a normal eye outward, 45' ; upward, 30' ; inward, 35' ; downward, 35'. 'the second card has a 3 mm. black point on one side, and a darker gray patch, having 3 the intensity of white, on the other. Each is seen on the perimeter are, outward, 70"; upward, 45’; inward, 55'; downward, 55'. Card 2 will reveal slight disturbances of light sense near the periphery, and card 1 in the intermediate and central zones. G 7 d Holden's tests are declared by their authors to be more delicate than color tests or at least equally so, while they possess the advantage of being more intelligible to patient
According to the experiments of londolt, the perception of the light is the most constant function of the healthy retina, and remains nearly the same throughout its surface, while the color- and a form-sense rapidly lessen toward the periphery. Progressive diminution of the light-sense, however, from center to periphery will be found if test-objects of varying luminous intensity with the illumination of ordinary daylight are employed. For practical purposes, in cases of very defective vision an ideal of the retina's sensibility to light may be obtained by passing a candle flame along the arm of the perimeter as a test object, while a second candle flame is made the point of fixation.'
The most frequent departures from those limits of the visual field assumed to be normal are general or concentric contraction ; contraction limited especially to one or the other side; peripheral defects in the form of reentering angles; absence of one segment or quadrant; and absence of the entire right or left half of the field (see page 472).
Scotomas. In addition to these defects, search should be made for dark areas within the limits of the visual field, or scotomas. These are distinguished as positive when they are perceived by the patient in his visual field, and negative when within the confines of a portion of the visual field the image of an external object is not perceived, but the affected area is not discovered until the field is examined. Negative scotomas are further divided into ab80lUte and relative. Within an absolute scotoma all perception of light is wanting, while within the confines of a relative scotoma the perception of light is merely diminished. The latter are color scotomas, usually for red and green. Scotomas are further subdivided, according to their situation and form, into central,, paracentral, ring, and peripheral.
In every normal eye there is a physiological scotoma which may be regarded as the type of an absolute scotoma corresponding to the position of the optic nerve entrance, which usually may be found 15' to the outer side of and 3' below the point of fixation, the distance from fixation being greater in hyperopic than in myopic eyes. This is known as Mariotte's blind spot. Usually the form of the blind spot is not round, but a vertical oval, its upper and lower end being somewhat drawn out to correspond to the larger retinal vessels. Its size depends upon the distance from the cornea. In Landoll's experiments on his own eve at a distance of 35 cm. from the cornea to the plane of projection the mean height of the blind spot was 52 mm. and its breadth 44 mm. The blind spot is much enlarged under certain conditions; for example, by retained marrow sheath or by papillitis.
For the detection of scotomata small test objects, white, gray, or colored, 1/4cm. square, are employed, which are moved in different directions from the point which the eye under observation attentively fixes, and the spot marked where the object begins to disappear or change its color. The arm of the perimeter is usually marked near the center in half degrees for this purpose. All examinations around the center of the field of vision, and hence the examinations for scotomata, are readily made upon a blackboard. Berry urges that the ordinary test for scotomata be supplemented by making an examination of the particular area of the field at a distance of 2 m. or more, so as to obtain a larger projection of the blind portion, and to be able to work with small retinal images without necessitating the use of very small objects.
Field of Fixation. This includes all points which the eve under observation can successively fix, the head being perfectly stationary. Various methods for determining the limits of the field of fixation have been employed; for example, watching the image of a candle flame on the center of the cornea as the eye follows the test light moved along the perimeter are until the limit of movement is reached. This method, suitable to amblyopic eyes, is not so accurate as one which requires the patient to distinguish letters. The patient is seated before the perimeter, with the semicircle horizontal, precisely as if his visual field was to be examined, and the eye under observation (the head being perfectly rigid) is made to follow a word composed of test letters representing the minimum acuteness of vision, and the point where vision ceases to be distinct marked in successive meridians.' Landolt's measurements of the field of fixation under normal conditions are as follows: Outward, 45 inward, 45' ; upward, 35 40'; downward, 60'.
Dr. G. T . Stevens determines the rotations of the eyes with a special instrument called a tropometer. According to his measurements, the most favorable rotations are Outward, 50' ; inward, 55' ; upward, 33'; downward, 50'. (See also p. 499.)
Tension. This term indicates the intraocular resistance, and is clinically demonstrable by palpating the globe with the finger tips. The middle and ring fingers are placed upon the brow of the patient, the tips of the index fingers upon the eyeball, and gentle to and fro pressure made, the eyes being directed downward. This pressure must be made in such manner as not to push the ball into the orbit; otherwise no information of its true resistance is obtained. The tension of one eye must always be compared with that of its fellow, and in any doubtful case the results may be contrasted with those obtained by examining an eye known to be normal in another patient of similar age.
Normal tension is expressed by the sign Tn, and the departures from it by the symbols + ?, + 1, + 2, + 3, and ?, 1, 2, 3: the plus signs indicate increased, and the minus signs decreased, resistance. In physiological experiments various kinds of apparatus, constructed upon the principle of the manometer, are employed, and or clinical purposes instruments known as tonometers have been devised. In practical work, however, sufficiently accurate data are obtainable by a careful use of the educated finger tips.
Protopsis, or protrusion of the eye, may be caused by orbital diseases, tenotomy, paralysis of the ocular muscles, and Graves's disease; while enlargement of the ball is the result of various conditions residing within the globe myopia, intraocular tumor, and staphyloma. lf the cause is unilateral, the resulting condition is asymmetrical and the two eyes may be compared by observing the relative positions of the apices of the Cornea with each other and with the line of the brows.
The eyeball is apparently shrunken (enophthalmos) in some cases of ptosis and in wasting of the orbital fat, and is diminished in size in high grades of hyperopia and congenital failures of development. As Nettleship has pointed out, the amount of exposed sclera decides the apparent protrusion or recession of the eyeball.
Position of the Eyes. Instead of presenting parallel visual axes, one eye may be deviated inward, outward, downward, or upward, constituting one of the various types of strabismus, a condition which may or may not be associated with diplopia.
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