In the cornea, the most common abnormality that reduces vision is scarring caused by trauma and infection. Ulceration and subsequent fibrosis may occur following recurrent herpes simplex, herpes zoster, and trachomatous infections of the cornea, or with certain mucocutaneous-ocular syndromes (Stevens-Johnson, Reiter). Hypercalcemia secondary to sarcoidosis, hyperparathyroidism, and vitamin D intoxication or milk-alkali syndrome may give rise to precipitates of calcium phosphate and carbonate beneath the corneal epithelium, primarily in a plane corresponding to the interpalpebral fissure—so-called band keratopathy. Other causes of corneal opacity include chronic uveitis, interstitial keratitis, corneal edema, lattice corneal dystrophy (amyloid deposition), and long-standing glaucoma. Polysaccharides are deposited in the corneas in some of the mucopolysaccharidoses (see Chap. 37), and copper is deposited in the Descemet membrane in hepatolenticular degeneration (Kayser-Fleischer ring). Crystal deposits may be observed in multiple myeloma and cryoglobulinemia. The corneas are also diffusely clouded in certain lysosomal storage diseases (see Chap. 37). Arcus senilis occurring at an early age (because of hyperlipidemia), sometimes combined with yellow lipid deposits in the eyelids and periorbital skin (xanthelasma), serves as a marker of atheromatous vascular disease.
In the anterior chamber of the eye, a common problem is impediment to the outflow of aqueous fluid, associated with excavation of the optic disc and visual loss, that is, glaucoma. In more than 90 percent of cases (of the open-angle type), the cause of this syndrome is unknown and a genetic factor is suspected. The drainage channels in this type appear normal. In approximately 5 percent of cases, the angle between iris and the peripheral cornea is narrow and blocked when the pupil is dilated (angle-closure glaucoma). In the remaining cases, the condition is a result of some disease process that blocks outflow channels—inflammatory debris of uveitis, red blood cells from hemorrhage in the anterior chamber (hyphema), new formation of vessels and connective tissue on the surface of the iris (rubeosis iridis), a relatively infrequent complication of ocular ischemia secondary to diabetes mellitus, retinal vein occlusion, or carotid artery occlusion. The visual loss is gradual in open-angle glaucoma and the eye looks normal, unlike the red, painful eye of angle-closure glaucoma that was described previously in reference to pharmacologic dilation of the pupil to facilitate fundoscopy.
Intraocular pressures that are persistently above 20 mm Hg may damage the optic nerve over time. This may be manifest first as an arcuate defect in the upper or lower nasal field or as a paracentral field defect, which, if untreated, may proceed to blindness. The classic finding in glaucoma is the Bjerrum field defect, consisting of an arcuate scotoma extending from the blind spot and sweeping around the macula to end in a horizontal line at the nasal equator. Other characteristic glaucomatous field patterns are winged extensions from the blind spot (Seidel scotoma) and a narrowing of the superior nasal quadrant that may progress to a horizontal edge, corresponding to the horizontal raphe of the retina (nasal step). The damage is at the optic nerve head, the optic disc appearing excavated, typically without pallor of the neuroretinal rim, thus distinguishing it from other optic neuropathies. Elongation of the optic cup in the vertical axis is typical. It is now appreciated that elevated intraocular pressure is only a concurrent finding and a risk factor for glaucoma, but similar optic nerve damage with “cupping” may be seen in patients with near normal pressure. This represents a major revision of the previous view that pressure was the elemental cause of damage in glaucoma.