Cone dystrophy is a rare disorder characterized by vision loss that may be mistaken for a bilateral optic neuropathy. Patients of any age can present with a gradually progressive decline in visual acuity and color vision. Photophobia and hemeralopia (“day blindness”) are common. In the early stages, the fundus can appear normal or show a slightly blunted foveal reflex with granular macular pigmentation. As the disease progresses, the macular RPE becomes atrophic in a central oval region. A “bull’s-eye” pattern of depigmentation may be present. Fluorescein angiography and fundus autofluorescence may reveal these abnormalities before they become clinically apparent. Full-field ERG results may be normal initially but eventually show markedly depressed photopic (cone) response and less prominently affected scotopic (rod) response. Multifocal ERG studies show central depression. OCT scans may show thinning of outer macular layers, loss of the ellipsoid zone, and outer cavitation.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.