DISORDERS IN RELATION TO THE EYE 705 



common. In neither case are other anomalies in structure or marking 

 noted. Theresult of operations on these eyes shows that their internal 

 organization is not normal (Hutchinson). In unilateral heterochromia, 

 the lighter eye is the expression of an incomplete albinism and the de- 

 velopmental disturbance is accentuated by the general development of 

 cataract. 



Retinitis Pigmentosa. (Abiotrophy of the retinal neuro-epithelium.) 

 This striking anomaly is generally accepted as a stigma of degeneracy. 

 It is very frequently associated with congenital deaf-mutism. Heredity 

 is a potent factor, and familial occurrence the rule. The factor of con- 

 sanguinity seems to be of importance only in connection with heredity and 

 environment (Shoemaker). Retinitis pigmentosa is not an inflammation, 

 but a degeneration of the entire neurovascular tract of the peripheral por- 

 tion of the end organ of vision, which probably extends centripetally well 

 toward the brain. The primary tissue involved is the layer of rods and 

 cones and the choroid, particularly the vessels, which are sclerosed and 

 narrowed, while the smaller branches are often entirely filled and clogged 

 by pigment masses which they carry into and deposit in the periphery of 

 the retinal fundus in the form of fine masses like feathers, lace or bone- 

 corpuscles. The disc is invariably waxy, dirty-looking, or white. There 

 are no macular changes. Central vision is rarely interfered with. The 

 field of vision shows marked concentric contraction with resultant telescopic 

 vision as in looking through a tube. 



At night and with lowered illumination sight is always very bad, 

 (hemeralopia) owing to early degeneration of the paracentral region of 

 the retina which is the most sensitive area to light in dark-adapted 

 eyes. This interferes with freedom and rapidity of orientation 

 and locomotion and causes the characteristic halting habitus of 

 the subjects. In a certain class of cases, retinitis pigmentosa sine 

 pigmento, only sclerosis of the choroid, retina, and vessels is found, with 

 the usual degenerative atrophy of the disc, and the thread-like veins and 

 arteries which are characteristic of the condition. Even in these origin- 

 ally unpigmented cases, however, deposits of pigment are found later 

 on in the disease and may be just as marked as in the typical cases. 



Cataract is a common accompaniment of retinitis pigmentosa, although 

 in some cases it is a comparatively late development. The lens changes 

 are usually found at or near the posterior pole with radially arranged 

 or branching opacities in the deeper cortical layers. Doyne, and Knapp, 

 note that extraction of these cataractous lenses gives unexpectedly good 

 visual results. 



1 It would appear that pigment emigration follows the stimulus of light and is 

 made possible or at least facilitated by vacuolization and other degenerative changes 

 in the neuro-epithelial cells of the retina. 



