This paper reviews the author's personal experience with genetic eye diseases and discusses the significance of family studies in providing key information for the advancement of molecular research. CHOROIDEREMIA: This disease has long been known as an X-linked progressive tapetoretinal degeneration, but it was first described in Japan in 1974 after finding asymptomatic fundus changes in heterozygous female carriers that are compatible with X chromosomal inactivation. Mutations in the disease-causing gene (REP-1) provide a clue to the diagnosis and pathophysiology of the disease. LEBER'S HEREDITARY OPTIC NEUROPATHY: The clinical expression is so variable among affected individuals and families that mild optic nerve disease of insidious onset should be differentiated from autosomal dominant optic atrophy. Molecular assessment of mitochondrial DNA leads to a definite diagnosis of the disease, but mitochondrial DNA mutations do not fully account for the clinical manifestation and phenotypic variability of the disease. NORRIE DISEASE: This rare X-linked vitreoretinal dysplasia, characterized by congenital bilateral blindness, was documented in Japan some twenty years ago and the disease has been identified in four unrelated Japanese families. The disease, once diagnosed on the basis of elaborate clinical and familial studies, can now be defined by molecular assessment of the Norrie disease gene. CONGENITAL NYSTAGMUS: A four-generation family was described which presented with autosomal dominantly inherited congenital nystagmus, peripheral corneal opacity, and foveal hypoplasia without any iris tissue malformation. The diagnosis of this family was established by detection of a missense mutation in the paired domain of the PAX 6 gene, hence conforming to a forme fruste of congenital aniridia. SORSBY'S FUNDUS DYSTROPHY: Two Japanese families with Sorsby's fundus dystrophy showed late-onset retinal dystrophy characterized by submacular hemorrhage and atrophy. Our patients presented with visual loss as late as 50 years of age or older due to macula-confined degenerative changes that were similar in all respects to exudative age-related macular degeneration and showed a novel mutation in the tissue inhibitor of the metalloproteinases-3 gene. AGE-RELATED MACULAR DEGENERATION (ARMD): We have studied whether there is any association of candidate polymorphic genes involving xenobiotic or antioxidant metabolism with susceptibility to ARMD. Preliminary results suggest that the genetic polymorphism of microsomal epoxide hydrolase is related to potential risk of ARMD.