Purpose: To clarify the pathogenesis of late-onset retinal degeneration (L-ORD), an autosomal dominant disorder characterized by thick deposits of lipid-rich material between the retinal pigment epithelium (RPE) and Bruch's membrane. Study Design: Comparative clinicopathologic case report and case series. Tissues: Eyes of an 82-year-old L-ORD eye donor and an age-matched control. Subjects: Five descendants of the eye donor and his affected sister. Methods: The eyes were processed for histopathologic examination, including electron microscopy and immunohistochemistry. Family members were examined clinically and with retinal function tests. Results: The L-ORD eye had sub-RPE deposits that were positive for lipid, including esterified and unesterified cholesterol. The deposits were thinnest in the macula, which retained the highest percentage of photoreceptors. In the periphery, RPE thinning and photoreceptor loss correlated with thickness of the sub-RPE deposits. The eye donor was asymptomatic until his late 50s, when he developed problems with adapting to darkness. At age 68, the eye donor had normal acuity but a midperipheral scotoma and subnormal electroretinograms (ERGs); visual loss was progressive. The five descendants (at the time of examination ages 44-58) of the eye donor and his affected sister, who were at 50/50 risk of inheriting L-ORD, had normal ERGs, but four showed defects in dark adaptation. The dark adaptation abnormalities had a distribution similar to the thickness of the sub-RPE deposits in the eye donor, with slow kinetics in the midperiphery and normal kinetics centrally. Conclusions: The L-ORD donor eye differed from a previous case in the regional distribution of sub-RPE deposits and photoreceptors. In the next generation of this L-ORD family, the first expression of disease, abnormal dark adaptation, mirrored the regional distribution of the deposits in the donor eye. The fine structure and staining characteristics of the sub-RPE deposits in L-ORD resemble those in age-related macular degeneration and Sorsby fundus dystrophy. (C) 2000 by the American Academy of Ophthalmology.