The commonest one, diabetes mellitus, causes characteristic diabetic retinopathy, ophthalmoplegia, cataract, and refractive errors. The cataract of hypoparathyroid tetany is its most serious irreversible change. Exophthalmos and lid retraction mean thyroid disease, even to laymen. Infections such as syphilis and histoplasmosis affect the eye with diagnostically characteristic destruction. Gonorrheal ophthalmia neonatorum was the commonest cause of childhood blindness before the development of effective prophylactic and therapeutic medications and would reappear immediately if these measures were discontinued.
Maternal rubella destroys eyes as well as hearts and brains.
Mucocutaneous disorders affect the delicate lid skin and conjunctiva just as other body surfaces. The permanent eye changes of Stevens-Johnson syndrome are the most disabling feature of this condition. The elastic tissue abnormality of pseudoxanthoma elasticum causes classic ruptures of the lamina vitrea of the fundus. Allergic and infectious blepharoconjunctivitis are extremely common skin disorders. Even chromosomal abnormalities affect the eye.