Cone and cone-rod dystrophies

Cone and cone-rod dystrophies are a group of genetically and phenotypically heterogeneous disorders. In cone dystrophy, the patients typically experience photophobia, reduced central vision, impaired colour vision, a variable degree of nystagmus and field loss. In cone-rod dystrophy, the patients also develop night blindness and peripheral field loss as the disease progresses. The onset of symptoms and the prognosis are variable.

Funduscopy can reveal a classic bull’s eye maculopathy although in some cases, only mild RPE disturbance is noted. In cases of cone-rod dystrophies, peripheral RPE atrophy and bone spicule pigmentation may be observed.

Autofluorescence and OCT imaging results are variable.

Full-field ERG is the gold standard for diagnosis and shows reduced single-flash and flicker responses in photopic conditions and normal response in scotopic conditions in cone dystrophy and early cone-rod dystrophy. The scotopic responses are also compromised in the later stage of cone-rod dystrophy.

Additional conditions not yet covered in this Atlas that should be considered in the differential diagnosis of bull's eye maculopathy are benign concentric macular dystrophy, Batten disease and Bardet-Biedl syndrome.

Gill JS, Georgiou M, Kalitzeos A, et al (2019) Progressive cone and cone-rod dystrophies: clinical features, molecular genetics and prospects for therapy. British Journal of Ophthalmology 103:711-720.