Feline mucopolysaccharidosis VI: General ocular and pigment epithelial pathology

Feline mucopolysaccharidosis VI (MPS VI) is a recessively inherited deficiency of arylsulfatase B (ASB). In the eye, the disease is expressed by the intracytoplasmic accumulation of vacuolated inclusions. These are present in connective tissue cells in the cornea, conjunctiva, sclera, choroid, and the stroma of the iris and ciliary body. In the iris and ciliary body epithelia, only the nonpigmented cells of the latter show presence of the disease. In the retinal pigment epithelium (RPE), a spatial and temporal distribution of the disease has been noted. In general, the nonpigmented RPE in the posterior pole is affected to a greater extent earlier in the disease; the peripheral pigmented RPE remains normal. Although hypertrophy of nonpigmented RPE cells causes disarray of the photoreceptor outer segments, their internal disc organization is not disrupted. Normal outer segment renewal rates and the presence of RPE phagosomes suggest that the diseased RPE is still able to function normally.