EYS encodes an EGF-like photoreceptor maintenance factor required for maintaining photoreceptor cell integrity and normal ciliary pocket morphology 1. By facilitating protein trafficking between photoreceptor inner and outer segments via the transition zone, EYS supports proper photoreceptor structure and function. Mutations in EYS cause retinitis pigmentosa 25 (RP25), an inherited retinal disease characterized by progressive photoreceptor degeneration. EYS is among the most frequently mutated genes in retinitis pigmentosa across multiple populations. In Japanese cohorts, EYS variants account for a substantial proportion of autosomal recessive RP cases, with specific founder mutations [p.(Ser1653fs) and p.(Tyr2935*)] and East Asian-specific variants identified 23. Genome-wide studies consistently rank EYS among the top three causative genes for inherited retinal diseases, alongside USH2A and RP1, explaining approximately 4% of cases in some populations 45. Copy number variations and single nucleotide variants in EYS contribute significantly to both solved and unsolved inherited retinal disease cases. Comprehensive genetic screening incorporating CNV analysis is essential for diagnosing EYS-associated retinal dystrophies 64.