CHE EYEBALL. 1447 



producing entropion. The eyelids become oedematous or ecchymotic from slight 

 causes, and in erysipelas are markedly swollen, closing the lids, or in severe cases 

 may become gangrenous, the exudate interfering with the blood-supply. 



Herpes zoster is sometimes seen along the cutaneous distribution of the frontal 

 and nasal branches of the trigeminal nerve. It is found on the forehead, lids, nose, 

 and even the cornea. The iris, ciliary body, or choroid may be involved, since 

 through the lenticular ganglion, the nasal nerve supplies these structures. The 

 cause is an inflammation of the trunk of the trigeminal nerve, the Gasserian ganglion, 

 or the lenticular ganglion. 



Hordeolum or stye is a suppuration of one of the sebaceous glands (Zeiss's 

 glands) associated with the follicles of the eyelashes. A chalazion is an affection of 

 one of the Meibomian glands, with occlusion of the duct and retention of the secre- 

 tion. There is often no inflammation present. For this reason, and because of 

 its situation on the under surface of the tarsal cartilage, it is often not noticed 

 until it reaches considerable size and shows through the lid. Normally the cilia or 

 eyelashes curve away from the surface of the eyeball. Sometimes from inflammation, 

 most commonly in trachoma or granular lids, they take the opposite direction and 

 irritate the cornea (trichiasis or wild hairs). 



The Conjunctiva. Congenital fatty growths occur rarely in the outer part of 

 the upper conjunctival sac. Dermoids and naevi have also been seen in the con- 

 junctiva. This membrane covers the anterior third of the eyeball, and where it passes 

 to the lids forms the fornices. Because the upper fornix is deeper than the lower, 

 being therefore turned less easily, foreign bodies are removed from the upper sac 

 with greater difficulty. These particles strike first on the surface of the globe, and 

 are usually brushed down into the lower sac by the upper lid. They frequently, 

 however, catch in the conjunctiva of the ball or of the upper lid, and are held in the 

 conjunctival sac only when they get above the upper retro-tarsal fold, where, if not 

 removed, they may set up a chronic inflammation, or remain unnoticed. They 

 have been found there months or even years afterward, entirely embedded in the 

 outgrowths of the inflamed conjunctiva (Fuchs). 



A pterygium is an elevated layer of conjunctiva and subconjunctival tissue, 

 triangular in shape with its apex near the edge of the cornea, and its base usually 

 towards the inner canthus. It tends to progress towards the pupil, but may stop 

 anywhere short of it. 



A pinguecula is a yellowish elevation of conjunctiva, to the inner side of the 

 cornea, sometimes to the outer side. It corresponds to the part of the conjunctiva 

 constantly exposed in the interpalpebral fissure, which therefore undergoes a change 

 in structure. That at the inner side is most marked and may become a pterygium later. 



The scleral portion of the conjunctiva is loosely applied to permit of free motion 

 of the ball. Near the margin of the cornea it becomes more fixed, and should be 

 caught there by the forceps in the effort to fix the eye when operating upon it. The 

 palpebral portion is more firmly attached, especially at the back of the tarsal plates 

 where it is more vascular, and where paleness is taken to indicate a general anaemia. 



In fractures of the base of the skull involving the roof of the orbit the hemor- 

 rhage into the orbital tissues shows first under the conjunctiva of the globe (subcon- 

 junctival ecchymosis). It finds its way under the conjunctiva of the lids later because 

 that is more firmly attached, and unless the lid is lifted, it will first be noticed at the 

 margin of the lid, after which it may grow upward under the skin. This is due to 

 the fact that the orbito-tarsal or palpebral ligament passes between the margin of the 

 orbit and the upper edge of the tarsal plate like a curtain and prevents the progress 

 of the blood forward to the skin until it has first passed down behind the tarsal plate 

 and under its lower margin. Owing to the thinness of the conjunctiva, oxygen per- 

 meates it more readily than it does the skin, so that blood under it retains its redness 

 instead of becoming dark, as under the skin of the lid in ordinary "black eye." 



THE EYEBALL. 



The eyeball is situated in the anterior part of the orbit, about 2 mm. nearei 

 the lateral than the nasal wall, and slightly nearer the superior than the inferior 

 wall. A line drawn from the superior margin of the orbit to the inferior is tangent to 



