First Author: T.Hasegawa JAPAN
Co Author(s): S. Tetsuka A. Yamaguchi C. Kobashi T. Sato Y. Tanaka A. Kakehashi
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We report a case of unilateral peripheral cone dystrophy and evaluate the associated clinicopathological changes using swept-source optical coherence tomography (SS-OCT).
A 39-year-old Japanese woman complained of a visual field defect of 2 years’ duration in the right eye. The patient underwent static visual field testing (Humphrey Field Analyzer 3, Carl Zeiss Meditec, Jena, Germany), colour vision testing (Ishihara test, Handaya, Tokyo, Japan), full-field electroretinography (ff-ERG) (LE-3000, Tomey, Tokyo, Japan), SS-OCT (DRI OCT Triton Plus, Topcon, Tokyo, Japan), and a routine ophthalmologic examination.
Her best-corrected visual acuity was 20/20 bilaterally. Funduscopy showed no abnormalities bilaterally. colour vision testing of each eye was normal. The static visual field test showed a relative paracentral scotoma with central sparing in the right eye. Horizontal three-dimensional (3D) macular analysis by SS-OCT showed retinal thinning in the parafoveal inferior area and the perifoveal nasal, inferior, and temporal areas in the right but not the left eye. Horizontal and vertical SS-OCT scans showed an unclear interdigitation zone (IZ) throughout the posterior pole except for the foveal zone in the right eye. The vertical 3D macular SS-OCT analysis showed thinning of the ganglion cell layer (GCL) and inner plexiform layer (IPL) corresponding to the IZ deficient region only in the right eye. ff-ERG showed normal flash ERGs and normal rod responses bilaterally. However, the cone response and flicker ERG decreased only in the right eye.
This is the first case report of unilateral peripheral cone dystrophy in which the GCL and IPL show pathological changes detected by SS-OCT. The OCT findings correspond well to the changes in the ERG and visual field abnormality. Because cone photoreceptor cells in the foveola are connected to retinal ganglion cells in a one-to-one correspondence without connection to the horizontal cells or amacrine cells, the GCL and IPL are not present in the foveal area. Based on this analysis, we speculated that the primary lesion of peripheral cone dystrophy is not in the cone photoreceptor cells but in the horizontal cells and/or amacrine cells. The clinicopathological changes in the ganglion cells and cone photoreceptor cells might be secondary changes due to pathologic horizontal cells and/or amacrine cells in peripheral cone dystrophy. The unilaterality found in the current case suggested that peripheral cone dystrophy is not a genetic disease.