Usher syndrome types I and II are clinical syndromes with substantial clinical and genetic heterogeneity. A study was undertaken to identify ocular symptoms and signs that could differentiate between the two types and assist in phenotype definition for molecular studies and in gentic counseling of affected patients. Sixty-seven patients with Usher syndrome were evaluated and based on audiologic and vestibular findings, were classified as Usher type I or II. Visual field area was calculated and used for further evaluation. P-values were calculated by logistic regression adjusting for age or by generalized estimating equations (GEE) regression, adjusting for age and correlation between fellow eyes. Best-corrected visual acuity, visual field area, electroretinography, the percentage of patients who developed cataracts as well as the percentage of patients who exhibited pigmentary or cystic macular lesions did not differ signficantly betweeen Usher type I and type II, respectively. The study concluded that an overlap between some ophthalmological manifestations of Usher type I and type II, namely measures of visual acuity and field, retinal function and the appearance of cataract and pigmentaary or cystic macular lesions. On the other hand, night blindness appears earlier in Usher type I (although the difference in age of appearance appears to be less dramatic than previously thought).
