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J. Tang, P. Lopez, L.M. Ayres, R.C. Caruso; Progression of Retinal Degeneration in Patients With Enhanced S Cone Syndrome . Invest. Ophthalmol. Vis. Sci. 2005;46(13):550.
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Purpose: Enhanced S cone syndrome (ESCS), initially described by Marmor et al. (1990), is an autosomal recessive disorder characterized by nyctalopia and varying degrees of visual acuity and visual field loss. These patients also have unique findings on electroretinogram (ERG) testing which include hypersensitivity of the S (blue) cone system. More recently, it has been discovered that a defect in a nuclear receptor gene (NR2E3) accounts for the disease seen in patients with ESCS. The purpose of this study was to analyze the long term changes in the full field ERG, visual fields, and dark adaptation in patients with ESCS. Methods: This was a retrospective case series of 2 patients with ESCS. The diagnosis of ESCS was confirmed by spectral ERG. Patient 1 was followed for 13.8 years and patient 2 was followed for 6.5 years using clinical examination, dark–adaptation, full field ERG and visual fields. The data from one eye of each patient was analyzed. Results: Assuming a constant loss model, combined ERG b wave amplitude declined 11.2% per year in patient 1 and 3.4% per year in patient 2. Similarly, flicker ERG amplitudes were reduced by 8.3% per year in patient 1 and 7.4 % per year in patient 2. In contrast, our patients maintained stability in central visual acuity and visual fields. Dark adaptation for both patients were elevated by 3 log units and remained at that level throughout the study period. Conclusions: Previous reports have postulated that because ESCS is a disorder of photoreceptor development, the disorder may be relatively stable over time. Long term analysis of our patients have yielded additional information to suggest that this condition is progressive leading to deterioration of ERG over time. One explanation may be that since the presence of healthy rod photoreceptors is necessary for the maintenance of other photoreceptor cells, replacing them with S cones would necessarily cause degeneration of other receptor cells.
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