Unilateral focal choroidal excavation in cone dystrophy

Abstract

An 18-year-old man presented with gradual and painless loss of vision in both eyes (BE) since the last 2 years. The symptoms were worse in day light and less in dim light. Best corrected visual acuity was 20/160, N 24 with a spherical equivalent of -6 D in BE. Colour vision showed complete red-green deficiency on Ishihara's test. Anterior segments and intraocular pressures were normal. Fundus examination of BE revealed scleral crescent at temporal disc margin, prominent choroidal vessels at posterior pole and symmetric well circumscribed atrophic lesions in both macula (figure 1A,B). Right eye (RE) additionally showed thinning in central macula bordered by hyperpigmentation. Fundus autofluorescence (AF) showed absence of flecks, hypo-AF centrally in BE corresponding to the fundus lesions, but much more prominent in the RE. There was a ring of hyper-AF surrounding these lesions (figure 1C,D). Optical coherence tomography (OCT) of RE showed central conforming subfoveal focal choroidal excavation (FCE). Outer retinal atrophy was noted involving the ellipsoid zone of BE with hyper-reflective areas below the external limiting membrane in BE (figure 2). Full field electroretinogram (ERG) of BE showed intact scotopic 3.0 responses, with absent single flash photopic 3.0 response (figure 2). Visual field tests for the central 10 degrees were not reliable due to excessive fixation losses in BE, though right eye showed a centre involving scotoma while BE had higher mean deviation thresholds (p<1%). The patient was diagnosed to have BE generalised cone dystrophy and high myopia with FCE in RE.