H12 THE ORGANS OF SPECIAL SENSE 



of bloodvessels may be seen on the cornea; and in interstitial keratitis new vessels extend into the 

 cornea, giving it a pinkish hue, to which the term salmon patch is applied. The cornea is richly 

 supplied with nerves, derived from the ciliary nerves, which enter the cornea through the fore part 

 of the sclera and form plexuses in the stroma, terminating between the epithelial cells by free 

 ends or in corpuscles. In cases of glaucoma the ciliary nerves may be pressed upon as they 

 course between the choroid and sclera (Fig. 800), and in consequence of the pressure upon 

 them, the cornea, to which they are distributed, becomes anesthetic. When a scar forms on the 

 cornea and the iris becomes adherent, the scar and the iris, and sometimes even the lens, may 

 bul^e forward from intraocular tension. This condition is staphyloma of the cornea. In con- 

 ditions of impaired nutrition the cornea may be bulged forward by intraocular pressure. The 

 line of least resistance is a little below the centre of the cornea, and it is bulged forward and 

 strongly curved. This condition is known as conical cornea. 



The snlera has very few bloodvessels and nerves. The bloodvessels are derived from the, 

 anterior ciliary, and form an open plexus in its substance. As they approach the corneal margin 

 this arrangement is peculiar. Some branches pass through the sclera to the ciliary body; others 

 become superficial and lie in the episcleral tissue, and form arches, by anastomosing with each 

 other, some little distance behind the corneal margin. From these arches numerous straight 

 vessels are given off, which run forward to the cornea, forming its marginal plexus. In inflamma- 

 tion of the sclera and episcleral tissue these vessels become conspicuous, and form a pinkish 

 zone of straight vessels radiating from the corneal margin, commonly known as the zone of ciliary 

 injection. In inflammation of the iris and ciliary body, this zone is present,' since the sclera 

 speedily becomes involved when these structures are inflamed. But in inflammation of the cornea 

 the sclera is seldom much affected, though the cornea and sclera are structurally continuous. 

 This would appear to be due to the fact that the nutrition of the cornea is derived from a different 

 source from that of the sclera. The sclera may be ruptured subcutaneously without any lacer- 

 ation of the conjunctiva, and the rupture usually occurs near the corneal margin, where the 

 tunic is thinnest. It may be complicated with lesions of adjacent parts laceration of the 

 choroid, retina, iris, or suspensory ligament of the lens and is then often attended with 'hemor- 

 rhage into the anterior chamber, which masks the nature of the injury. In some cases the lens 

 has escaped through the rent in the sclera, and has been found under the conjunctiva. Wounds 

 of the sclera, if they do not perforate, usually heal readily. If they extend through the sclera 

 they cause diminished tension, are always dangerous, and are often followed by inflammation, 

 suppuration, and by sympathetic ophthalmia. The sclera may be weakened by injury, inflam- 

 mation, etc., and the weakened portion may bulge from intraocular pressure, and even a healthy 

 sclera may bulge from excessive intraocular pressure. According to its situation the lesion is 

 known as ciliary staphyloma, equatorial staphyloma, or posterior staphyloma. 



One of the functions of the choroid is to provide nutrition for the retina and to convey ves- 

 sels and nerves to the ciliary body and iris. Inflammation of the choroid is therefore followed 

 by grave disturbance in the nutrition of the retina, and is attended with early interference with 

 vision. Purulent choroiditis is not confined to the choroid; the retina, the vitreous, and the entire 

 uveal tract become involved, and even other structures may suffer. In its diseases it bears a con- 

 siderable analogy to those which affect the skin, and, like it, is one of the places from which 

 melanotic sarcomata may grow. These tumors contain a large amount of pigment in their cells, 

 and grow only from those parts where pigment is naturally present. The choroid may be rup- 

 tured without injury to the other tunics, as well as participating in general injuries of the eyeball. 

 In cases of uncomplicated rupture the injury is usually at its posterior part, and is the result of a 

 blow on the front of the eye. It is attended by considerable hemorrhage, which for a time may 

 obscure vision, but in most cases this is restored as soon as the blood is absorbed. 



The iris is the seat of a malformation, termed coloboma, which consists in a deficiency or cleft, 

 which in a great number of cases is clearly due to an arrest in development. In these cases it is 

 found at the lower aspect, extending directly downward from the pupil, and the gap frequently 

 extends through the choroid to the attachment of the optic nerve. In some rarer cases the gap 

 is round in other parts of the iris, and is then not associated with any deficiency of the choroid. 

 The iris is abundantly supplied with bloodvessels and nerves, and is therefore very prone to 

 become inflamed. When inflamed, in consequence of the fact that the iris and ciliary body are 

 continuous, and that their vessels communicate, iritis is usually associated with cyclitis, the dis- 

 ease being called iridocyclitis. And, in addition, inflammation of adjacent structures, the cornea 

 and sclera, is apt to spread into the iris. The iris is covered with endothelium, and partakes of 

 the character of a serous membrane, and, like these structures, is liable to pour out a plastic exuda- 

 tion when inflamed, and contract adhesions, either to the cornea in front (synechia anterior], or 

 to the capsule of the lens behind (synechia posterior}. In iritis the lens may become involved, 

 and the condition known as secondary cataract may be set up. Tumors occasionally commence 

 in the iris; of these, cysts, which are usually congenital and sarcomatous tumors, are the most 

 common and require removal. Gummata are not infrequently found in this situation. In some 

 forms of injury of the eyeball, as the impact of a spent shot, a flying cork, the rebound of a twig, 

 or a blow with a whip, the iris may be detached from the Ciliary muscle, the amount of detach- 



