Diseases of the Eye.— The morbid changes of the eye and its appendages vary according to the site of the disease. The causes of dis eases are in a general way physical, me chanical, chemical or parasitic. The eye is very tolerant to radiant heat, because the media of the eye, which contain a large amount of water, absorb the heat rays, and do not per mit them ta reach the retina. Injury to man by ultra violet rays in sun light occurs only under very unusial circumstances. Snow blind ness is due to the erythema of the lids caused by the ultra violet rays, with consequent conjunc tivitis and photophobia. Injunes to the eye ball are of two kinds —the direct and the in direct. In direct injury the damage done de pends upon the nature of the instrument —as when a lcnife perforates the globe only tissues in contact with the blade are harmed. But when the globe is strucic by a baseball or stone, in direct injury, the harm done depends more on the anatomy of the organ. For instance, a se vere blow on the cornea may cause detachment of the retina, rupture of the chorioid, or dis location of the lens. Foreign bodies entering the globe are received with different degrees of tolerance. Thus, organic substances, as cilia or particles of wood may become incapsulated, causing no subsequent trouble. But steel in the interior of the globe becomes oxidized by the fluids and being deposited in the uvea causes siderosis bulk Hence the importance of its speedy removal. Copper, of all foreign substances in the globe, is the least tolerated. A small chip is sufficient to produce violent in flammation and loss of the eye. The trau matic uveitis in one eye caused by a per forating. wound sometimes produces a similar disease in the uninjured eye—sympathetic in flammation.
The most frequent systemic diseases giving rise to ocular disturbances are syphilis, tubercu losis, rheumatism, nephritis, diabetes, arterio sclerosis, diseases of metabolism and chronic in toxications. Between the ages of 5 and 15, in inherited syphilis, the cornea often becomes the seat of a cellular infiltration with new-formed blood vessels — the salmon patch — interstitial keratitis. Those afflicted with the disease usu
ally exhibit a peculiar fonmation of the face and head. The bridge of the nose is sunken in. The frontal eminences are very prominent. The incisor teeth are abnormally shaped (Hutchin, son's teeth). Frequently there is accompanying hardness of hearing. Bad teeth are not infre quently the cause of ocular symptoms and disease—as chronic iritis,—which clears up when the mouth receives proper attention. Other foci causing ocular disorders may be located in the tonsils, accessory nasal sinuses and intestinal tract. Acromegaly exhibits many ocular manifestations, as hypertrophy of the margins of the orbit and thickening of the skin —of the lids. The accompanying. disease of the pituitary body causes characteristic bitemporal hemianopsia. °Graves Disease') produces exophthalmus, sometimes so great that the lids can no longer cover the eyes. Acquired syphilis is responsible for at least 25 per cent of all cases of iritis. Atrophy of the optic nerve is found above all in tabes. It usually develops in the initial stage of tabes, at a time when the ataxic symptoms are slight or absent. Another eye symptom which likewise makes its appear ance early in this disease is the Argyll-Robert son pupil, in which the pupil reacts to accommo dation and convergence, but not to light.
Many cases of impaired vision (ambly opia) and of blindness (amaurosis) are due to poisons introduced into the system which affect the optic nerve. Chief among these poisons are alcohol and tobacco, alone or combined. Other poisons causing amblyopia are lead, quinine and chloral. Nephntis (Brights Disease) may cause oedema of the lids and albuminuric retinitis. Diabetes produces cata ract and hemorrhages in the retina.
Fuch's 'Text Book of Ophthalmology) (Philadelphia 1917) • Week's 'Diseases of the Eye); Salzmann, ''Anatomy and Histology of the Human Eye-Ball' (Chicago 1912) •, May, 'Manual of the Diseases of the Eye) (New York 1914).