THE CR YSTALLINE LENS 



1113 



ment varying from the slightest degree to the separation of the whole iris from its ciliary con- 

 nection. 



The Argyll-Robertson pupil shows no reaction to light, but retains reaction to accommodation 

 and vision remains good. 



The retina, with the exception of its pigment layer, and its vessels is perfectly transparent, 

 and is invisible when examined by the ophthalmoscope, so that its diseased conditions are rec- 

 ognized by its loss of transparency. In retinitis, for instance, there is more or less dense and 

 extensive opacity of its structure, and not infrequently extravasations of blood into its sub- 

 stance. Hemorrhages may also take place into the retina from rupture of a bloodvessel without 

 inflammation. In optic neuritis, papil/itis, or choked disk, the ophthalmoscope shows increase 

 in vascularitv, and swelling and opacity of the nerve, which extend beyond the disk margins. 

 Optic atrophy is apt to follow. (Fig. 821 shows a normal optic disk.) The retina may become 

 displaced from effusion of serum between it and the choroid or by blows on the eyeball, or may 

 occur without apparent cause in progressive myopia, and in this case the ophthalmoscope shows 

 an opaque, tremulous cloud. Glioma, a form of sarcoma, and essentially a disease of early life, 

 is occasionally met with in connection with the retina. 



The lens has no bloodvessels, nerves, or connective tissue in its structure, and therefore is 

 not subject to those morbid changes to which tissues containing these structures are liable. Is 

 does, however, present certain morbid or abnormal conditions of various kinds. Thus, variation^ 

 in shape, absence of the whole or a part of the lens, and displacements are among its congenital 

 defects. Opacities may occur from injury, senile changes, malnutrition, or errors in growth or 

 development. An opacity of the capsule, of the lens, or of both, is known as a cataract. Senile 

 changes may take place in the lens, impairing its elasticity and rendering it harder than in youth, 



FIG. 821. Ophthalmoscopic appearance of healthy 

 fundus in a person of very fair complexion. Scleral 

 ring well marked. Left eye, inverted image. (Wecker 

 and Jaeger.) 



FIG. 822. Ophthalmoscopic appearance of severe 

 recent papillitis. Several elongated patches of blood 

 near border of disk. (After Hughlings Jackson.) 



so that its curvature can only be altered to a limited extent by the Ciliary muscle. And, finally, 

 the lens may be dislocated or displaced by blows upon the eyeball, and its relations to surround- 

 ing structures altered by adhesions .or the pressure of newgrowths. 



There are two particular regions of the eye which require special notice; one of these is known 

 as the " filtration area," and the other as the " dangerous area." The filtration area is the circum- 

 corneal zone immediately in front of the iris. Here are situated the cavernous spaces of Fon- 

 tana. which communicate with the canal of Schlemm, through which the chief transudation of 

 fluid from the eye is now believed to take place. The dangerous area of the ei/e is the region in 

 the neighborhood of the ciliary body, and wounds or injuries in this situation are peculiarly 

 dangerous: for inflammation of the ciliary body is liable to spread to many of the other structures 

 of the eye, especially to the iris and choroid, which are intimately connected by nerve and vas- 

 cular supplies. Moreover, wounds which involve the ciliary region are especially liable to be 

 followed by sympathetic ophthalmia, in which destructive inflammation of one eye is excited by 

 some irritation in the other. 



Emmetropia is normal vision. In normal vision the practically parallel light rays from distant 

 objects focus on the retina without effort; divergent rays from near objects are focussed on the 

 retina by an effort of accommodation. 



Hyper opia or hypermetropia is far-sightedness. In this condition the retina is in front of the 

 principal focus when the eye is at rest. The patient endeavors to correct the failure by constant 



