Acta Ophthalmol Scand 2002 Apr;80(2):196-201
Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Purpose: Usher syndrome types I and II are clinical syndromes with substantial genetic and clinical heterogeneity. We undertook the current study in order to identify ocular symptoms and signs that could differentiate between the two types.
Methods: Sixty-seven patients with Usher syndrome were evaluated. Based on audiologic and vestibular findings, patients were classified as either Usher type I or II. The severity of the ocular signs and symptoms present in each type were compared.
Results: Visual acuity, visual field area, electroretinographic amplitude, incidence of cataract and macular lesions were not significantly different between Usher types I and II. However, the ages when night blindness was perceived and retinitis pigmentosa was diagnosed differed significantly between the two types.
Conclusions: There seems to be some overlap between types I and II of Usher syndrome in regard to the ophthalmologic findings. However, night blindness appears earlier in Usher type I (although the difference in age of appearance appears to be less dramatic than previously assumed). Molecular elucidation of Usher syndrome may serve as a key to understanding these differences and, perhaps, provide a better tool for use in clinical diagnosis, prognosis and genetic counseling.