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Circulation of the Choroid

Circulation of the Choroid, Ciliary Body and Iris. The following details of the circulation of the choroids and iris and ciliary body are those enunciated by Leber, whose researches have thrown new light on many points.

The structures which have just been described (choroids, ciliary body and iris) received their arterial blood from the ciliary arteries, which are classed as posterior ciliary arteries (direct branches from the ophthalmic artery), and anterior ciliary arteries (arising from the arteries of the recti muscles). The short posterior ciliary arteries, about twenty in number, perforate the sclerotic near the entrance of the optic nerve. They divide dichotomously in the choroids, and distribute themselves rapidly over it till in the neighborhood of the ora serrata.

Starting from their entrance into the choroids, they send branches to the capillary layer, in which, finally, all their ramifications are lost, with the exception of a few branches which pass the ora serrata to anastomose with branches of the anterior ciliary arteries and with the long posterior ciliary arteries. The direct transformation of these arteries into veins does not exist. The anterior portions of the choroids, situated beyond the ora serrata, receive their arterial blood form the long posterior ciliary arteries, and from the anterior ciliary arteries. Those arteries (long posterior ciliary), having pierced the sclerotic very obliquely near the optic nerve, follow a course in the external layer of the choroids (membrane supra chorodea), until they reach the ciliary muscle, where they divide into two branches, which diverging from each other, pierce the muscle, and, at its anterior border, assist in the formation of the great arterial circle of the iris.

The anterior ciliary arteries, five or six in number, reach the sclerotic by piercing the insertions of the recti muscles. On the sclerotic they are directed towards the margin of the cornea, and in their course send some branches into the interior of the eyeball. These branches perforate the sclerotic, and, in the ciliary muscle, unite with the long posterior ciliary arteries to form the great arterial circle of the iris, at the margin of the ciliary muscle, and a second arterial circle situated in the midst of the substance of the muscle itself. Form these arterial circles arise: - (1) Arteries for the supply of the anterior part of the choroid, recurrent branches which anastomose with the short posterior ciliary arteries, and finally form the capillary system; (2) the arteries of the cialiary muscle – these are in the form of a very fine capillary network, the meshes of which run parallel with the muscular fibres of this structure; (3) the arteries of the ciliary processes – these pierce the ciliary muscle before reaching the process, and divide into a great number of ramifications, which form anastomoses, and terminate in the veins at the free margin of the processes, although, as yet, we are unable to decide whether they are transformed directly into veins or undergo the capillary transformation ; (4) the arteries of the iris, which are carried very near to the anterior surface of the membrane, radiating towards the papillary margin.

In their course they anastomose frequently with each other, forming little loops, and sending some ramifications towards the posterior surface of the iris, which there form a large meshed capillary margin unite to form the small arterial circle of the iris; others are directed as fine ramifications to the border itself, where, curving on themselves so as to form dilatations, they assume the character of veins. Previously, they furnish some small branches to the sphincter of the iris, where they form a very fine capillary network.

The venous blood from the iris, ciliary body and choroids, leaves the eye for the most part by the star-shaped veins of the choroids (vasavorticosa). The veins of the iris are united to those of the ciliary processes, with which, also, the veins of the ciliary muscle are in part of blended, so as to form a serrated network on the internal surface of the ciliary processes, facing the choroids. It is only when they reach the margin of that membrane that their veins dip so as to come to the external surface.

The veins of the ciliary processes and of the iris do not traverse the ciliary muscle ; whilst the arteries, as we have already seen, pierce it, to be distributed to the processes and iris. Thus, constractions of the ciliary muscle exercise an influence only on the arterial circulation, and, during accommodation, the ciliary processes diminish in size, but become swollen when accommodation is at rest. After the veins of the iris and ciliary body have united in the choroids, they run from before backwards to the star-shaped veins, by which all the venous blood of the choroids leaves the eyeball. These star-shaped veins, situated near the equator of the eye, thus receive, in addition to the veins already mentioned, those of the anterior parts of the choroids, of which a certain number are united to the veins of the ciliary processes, and to those of the posterior part of the choroids. These last are situated between the short ciliary arteries, so that these vessels exercise a mutual pressure on each other, from which it may be presumed that they regulate the supply in these parts. Thus, the stream of blood following the same direction from before backwards, in both the arteries and the veins, the distention of the arteries will accelerate, by consecutive compression, the circulation in the veins, whilst the distention of these latter will retard the current of blood in the arteries.

All the veins of the choroids thus converge from different points, and terminate in a branch which perforates the sclerotic. It is by this arrangement that the star-shaped veins are formed; of these we generally find four or six, which anastomose by tolerably large branches.

A portion of the venous blood from the ciliary muscle leaves the eyeball by another route than that which we have just described. A dozen or fourteen small veins perforate the sclerotic near the margin of the muscle, and, while dividing so as to anastomose, run towards the ciliary venous plexus (canal of schlemm), with which a large proportion are incorporated, whilst a few join the anterior ciliary veins of the subconjunctival tissue. From the canal of Schlemm, several veins, having previously perforated the sclerotic, go towards the margin of the cornea ; others spread out in the venous episcleral network.

There are thus two ways by which the venous blood from the iris, ciliary body and choroids is brought to the surface ; a posterior passage by the star-shaped veins, which is much the larger, and an anterior passage, which has just been described. In the case of hyperemia, or of intraocular pressure, such as to compromise the star-shaped veins at the point where they pierce the sclerotic, the blood by preference takes the anterior passage, and we then see an increase in number and size of the anterior ciliary veins.

The nerves of the choroids, ciliary body and iris come from the ophthalmic ganglion, and from the naso-ciliary nerve. Arising from the gangalion, ten to twenty nerves (short ciliary nerves), having perforated the sclerotic near the optic nerve, enter the choroids ; there they supply the verve elements which we have already described, or run between choroids and sclerotic to the ciliary body. The nerves coming from the naso-ciliary (long ciliary nerves) perforate the sclerotic near the insertion of the superior oblique muscle. They go to the ciliary muscle, where they divide and anastomose with the short ciliary nerves. It is from this network that the nerves of the iris come, which follow almost the same course as the vessels. Their mode of termination is not exactly known.

ART. I – Hyperemia of the Iris.

The first symptom which hyperemia of the iris produces is congestion of the episcleral tissue, the vessels of which are, as we have seen, closely connected with those of the iris. Hence, we find a more or less intense pericorneal injection. Another symptom consists in the impaired effect of atropine of the contraction of the pupil ; it dilates it, but with difficulty, and for a shorter time than in a normal eye. If we find this condition, we must make sure that it does not depend on an affection of the cornea preventing or retarding the action of the remedy, or on the presence of adhesions of the papillary margin (posterior synechia).

The third symptom of hyperemia of the iris consists in a change in the coloration of this membrane, due to the circumstance that a yellowish-red tint is added to its natural color. Thus a blue iris becomes slightly yellowish ; a brown iris takes on a rose tint. This discoloration is so much the more apparent in simple hyperemia of the iris, that the aqueous humor preserves its transparency, and that the tissue composing the membrane is not the seat of exudations as in iritis. In cases of very chronic hyperemia (for example, after the operation for solution of cataract), the change of coloration of the iris depends also on alterations of the pigmentary cells of the iris stroma, accompanied with atrophy of the pigment which forms the extreme margin of the pupil, the contour of which thus loses its regularity and appears dentated. Advancing years also produce an analogous alteration, and cause the iris to lose its usual brilliancy, without any symptom of inflammation.

Hyperemia of the iris passes off with the removal of the exciting cause, without leaving any trace ; or it may lead to iritis, either spontaneous or secondary to an irritating course of treatment – as, for example, the use of nitrate of silver lotion.

Etiology. – hyperemia of the iris always precedes and accompanies inflammation of this membrane. It is also found in hyperemic or inflammatory affections of the structures in vascular connection with the iris. Thus hyperemia of the iris is formed as a consequence of excessive and prolonged efforts of vision, and in inflammations of the anterior parts of the choroids and ciliary body. It is also observed in ulcerative or traumatic affections of the cornea and in inflammation of the conjunctiva, acute granulations, and phlyctenular ophthalmia, especially if these affections have been carelessly treated with irritants.

Our treatment ought to be directed to the cause of the hyperemia, as well as to the local congestion. We should recommend absolute rest for the eyes and the avoidance of everything which is likely to increase the congestion ; for example., a too brilliant light and general congestions to the head. We should also recommend the prolonged use of atropine or duboisine, so as to give complete rest to the internal muscles of the eye.

ART II – Iritis

Inflammation of the iris adds to the symptoms of hyperemia already described that of the production of an exudation. This exudation may be formed: -

(a) at the margin of the pupil and on the posterior surface of the iris, where it is very apt to produce adhesions between the iris and the capsule of the lens (posterior synechia).

(b) on the anterior surface of the iris, in the aqueous humor and on the membrane of descemet. On the anterior surface of the iris, it assumes the form of a very thin fibrinous structure, which destroys the brilliancy of the membrane, giving to it the apprearance of an unpolished surface. It also often extends to the papillary field. In the aqueous humor, it produces either general haziness, or flocculi, or small floating membranes, which may gravitate to the bottom of the anterior chamber (hypopyon).

Finally, this exudation may affect the membrane of descemet, there forming a slight cloud or punctuate deposits.

(c)in the parenchyma of the iris itself, increasing the volume of the membrane or producing papillary excrescences.

We shall have to distinguish several forms of iritis – simple or plastic iritis, serous iritis, parenchymatous iritis, and, as special form of this last variety, syphilitic iritis.

A. Simple or Plastic Iritis

The pericorneal injection in this form is more or less pronounced according to the intensity of the inflammation. In severe cases, it is even accompanied with cedema of the subconjunctival tissue, producing a chemosis, which to some extent masks the injection around the cornea. The aqueous is somewhat muddy; the iris itself is more or less deficient in brilliancy and changed in color; and the pupil, generally contracted, is perfectly immobile, excessively sluggish in its movements.

When the affection has already led to the formation of adhesions between the margin of the pupil and the lens, the outline of the pupil is irregular; or, if at first sight and the lens, the outline of the pupil is irregular; or, if at first sight it seems normal, its irregularities become apparent by focal illumination or by using atropine. By this remedy the as yet feeble adhesions are often at once torn asunder, and the pupil then regains its circular form.

In such cases we often see the debris of these syneche and of the pigment of the iris on the capsule, where they indicate the position of the adhesions. Again, deposits of exudation, varying in their form, may exist in the papillary field itself. In other cases, the synechia resist the action of atropine, which then only dilates those portions of the iris which are still non-adherent, and this irregular dilatation may cause the pupil to assume the most varying forms.

These adhesions are sometimes limited, sometimes large, isolated and more or less numerous; or the margin of the pupil may adhere to the capsule throughout its entire extent. To this condition the term complete or annular synechia has been applied.

When at the same time the exudation completely fills the papillary field, it produces occlusion or obliteration of the pupil.

B. Serous Iritis

Instead of the plastic exudation, which characterizes simple iritis, we observe here a hypersecretion of the aqueous humor, which is at the same time muddy, and which precipitates deposits of variable size and form on the posterior surface of the cornea and on the capsule of the lens. The pericorneal injection is often very slight, and the appearance of the iris is apparently changed by the haziness of the aqueous and of the cornea.

The anterior chamber is deeper, the intraocular pressure increases, and, in consequence of the disturbance of the nerves thus produced, the pupil is semi-dilated, and remains nearly immobile. In slight cases, the haziness of the aqueous humor and descemet’s membrane is often so inconsiderable that it is discovered only on very careful examination. We then find a general cloudiness produced by the suspension of the solid particles in the aqueous humor, or, in more pronounced cases, flakes which float in the humor, and gravitate to the bottom of the anterior chamber. This haziness disappears if we permit the deposit to escape by paracentesis.

The posterior surface of the cornea presents a slight general opacity, intermingled with grayish points, varying from a very fine point to the size of a pin head, or even larger. The alterations of the membrane of descent, which, in addition of these deposits, may consist in modifications of its epithelial layer, are frequently accompanied with opacities of the vitreous (irido-choroiditis).

The deposits on the membrane of descement, and on the capsule of the lens, were formerly considered as the origin of the disease. It was believed that the disease consisted in inflammation of a hyaloid membrane which was thought to line the anterior and posterior chambers as a serous sac connected with the envelope of the vireous. This disease was then called aquo-capsulitis, hydromeningitis, desemetitis.

C. Parenchymatous Iritis

In this variety of iritis the inflammation of exudation affect the elements of the tissue composing the membrane, which increases in thickness either throughout its entire extent or partially.

Thus we have a swelling and a hypergenesis of the cellular elements, in addition to which there is a disturbance of the circulation, followed by the appearance of tortuous vessels on the anterior surface of the membrane. This swelling is further increased by a plastic or purulent effusion in the parenchyma, at the margin or on the surface of the iris. These exudations unite the papillary margin to the capsule, in the form of pigmented synechia, rendering the pupil immobile. The space which separates the posterior surface of the lens from the iris, as also the pupillary filled with grayish or yellowish material ; effusion into the interior chamber likewise takes place, and can give rise to an extensive hypopyon.

The aspect of the anterior surface of the iris varies according as the disease is general or more definitely localized. It always appears tarnished, discolored and swollen, with isolated pigment spots due to the hypergenesis of the cells of the stroma. But in the first case this appearance is general ; in the second it is seen near the free border or in the continuity of the membrane, either as deeply-colored papilli form excrescences, or as small yellowish tubercles surrounded with vessels. These nodosities rise above the level of the iris, and are insensibly lost in its tissue.

This condition of the iris is accompanied, especially in the primary stages of a severe case, with a well marked pericorneal injection, with conjunctival congestion and with chemosis. The lids even may participate in the irritation, especially the superior eyelid, which becomes red, shining and cedematous.

D. Syphilitic Iritis

Syphilitic iritis may present itself in the form of any of the varieties of iritis which we have just described. Nevertheless, there exist a form of partial parenchymatous iritis, which is very often met apart from any specific manifestation, but yet so frequently in conjunction with constitutional syphilis, that it may be considered as characteristic of this diathesis.

In syphilitic iritis only a small portion of the membrane changes its color, becomes swollen and vascular, and takes on a red, yellowish or brownish tint. This small tumor, of variable dimensions, extends sometimes considerably beyond the level of the iris, and resembles in its structure a gummatous tumor in its early stage. Several may be observed at the same time. They rarely undergo a fatty or purulent degeneration ; in most cases they disappear as do the nodosities of degeneration ; in most cases they disappear as do the nodosities of the parenchymatous iritis, generally by absorption, and the tissue of the iritis atrophies at the affected spots. In this variety of partial iritis the pericorneal injection also appears most quickly towards the portion of the corneal margin which is nearest to the seat of the alteration.

In the different forms of iritis which have just been described, the subjective sensations, such as pain, photophia, disturbance of vision, etc., are present with very variable intensity.

Pain is sometimes entirely absent; it is, as a rule, more acute in parenchymatous and simple iritis than in the serous form, and probably arises from compression of the ciliary nerves by the hyperemia tissue or by the exudation. Thus in slight cases there is often only a sensation of heat and of heaviness in the eye; in other cases the patients complain of lancinating pains in the suborbital region, in the forehead, and in the parts supplied by the contiguous branches of the fifth pair.

The pain, as a rule, increases towards the evening and during the night, so as entirely to deprive the patient of sleep. The lanchrymation and photophobia vary with the intensity of the ciliary pain, without ever being pronounced as in keratitis.

Disturbance of the vision depends essentially on the affection of the aqueous humor and on the effusions which are formed in the pupillary field. Therefore, when we find a greater diminution of the acuteness of vision than is accounted for by these alterations, or defects in the pupillary field, our attention should be directed to the complications which so frequently occur in certain forms of iritis (choroiditis and opacities of the vitreous body).

When the invasion of iritis is very acute, in a feeble or irritable disturbance, and even by vomiting.

Progress and Termination – when iritis follows an acute course, it soon attains its maximum intensity, and imperceptibly disappears at the end of three or four weeks. The pericorneal injection grows pale, the conjunctiva becomes white, the pupil is dilated, regaining its circular form, and the effect of atropine is increasingly strong. The exudations are absorbed, and the iris assumes its normal condition.

Traces of synchia are sometimes seen to remain on the capsule or the lens, as small pigmentary spots, which even after the lapse of years indicate the existence of a previous iritis. Notwithstanding this complete cure, there remains for a certain time a great liability to relapse, especially if the muscles of the iris have not been kept at rest by the prolonged use of atropine.

This favorable course of iritis may take from a few weeks to a few months. Serous iritis, although more chronic, often passes off without leaving any trace; simple iritis much more frequently causes synechia, which do not yield readily to treatment ; parenchymatous aritis, if it be developed in conjunction with or after a simple iritis, rarely admits of perfect repair of the affected tissue.

In a second series of cases the iritis is cured; but posterior synechia have been formed, which are too strong to yield to the action of atropine. If they are not numerous and isolated, they may exist without any serious consequences; but these adhesions often exercise a most baneful influence on the eye, because they produce incessant dragging of the membrane, during the movements to which the iris is constantly subjected by the action of light and of accommodation ; they thus disturb the circulation and innervation. This danger is so much the greater in proportion as the synechia are large and numerous. Indeed, they explain the frequency of relapses, which formerly were by common consent ascribed exclusively to a general diathesis. In each of these new attacks, the disease becomes worse, because the synechia already existing hinder the action of the atropine, and because additional synechia are formed each time, thus rendering the communication between the anterior and posterior chambers of the eye more and more difficult, a communication which is essential to the equilibrium of the intraocular pressure and to the normal nutrition of the media of the eye. Again, when a complete posterior synechia is a formed, with or without the obliteration of the pupil, this communication is entirely stopped; the aqueous humor and liquids secreted behind the iris push that membrane forwards towards the cornea, and, as it is retained at its pupillary margin by adhesion to the capsule, the peripheral portions of the membrane alone can yield to this pressure ; hence the iris assumes a funnel-shaped appearance.

In these cases, the inflammation spreads to the ciliary processes an to the choroids, the tension of the eye increases, and glaucomatous symptoms are produced (hardness of the eyeball, venous congestion, anesthesia of the cornea, characteristic retraction of the visual field). Later, the iris and choroids atrophy, the hyper-secretion ceases, the eyeball gradually softens, and at the same time a calcareous cataract is formed. We shall have to revert in greater detail to this complication to which the name irido-choroiditis has been given, and which often.

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