Abstract
Abstract: :
Purpose: To evaluate the hypothesis that poor vision since birth results in a similar lack of emmetropization in patients with different causes of low vision: autosomal recessive achromatopsia (rod monochromacy; RM, N=96), x-linked achromatopsia (blue cone monochromacy, BM, N=27), ocular albinism (OA, N=36) and oculocutaneous albinism (OCA, N=133). Methods: Refractive error was determined by cycloplegic retinoscopy (RM, BM) or through record review (OCA, OA). Three components of refractive error were compared: equivalent sphere and astigmatism expressed as primary and oblique crossed cylinder components. Visual acuity was measured using a Bailey-Lovie chart under dim illumination. Results: The table shows the median and range between the 25th-75th percentiles for all groups for the three refractive components compared to a sample (N=505) of a visually normal clinical population. The spherical equivalent refractive errors ranged from moderately high myopia in the BM group to near emmetropia in the RM and OA groups to low hyperopia in the OCA group. Large amounts of astigmatism characterized all low vision groups. The OCA group had the largest astimatic error. Visual acuity was better for patients with albinism (20/125) than achromatopsia (20/172). The OA group had significantly better visual acuity than the OCA group (20/96 vs. 20/132). There was no difference in acuity between the RM and BM groups. No correlation was found between visual acuity and any refractive component. Conclusions: The distributions of spherical equivalent refractive error differed significantly among patient groups in spite of all having low vision since birth. The distributions were unusually broad and in some cases appeared bimodal. Primary astigmatism of large amount ("with the rule") was present in all patient groups. Only the blue cone monochromats have significant oblique astigmatism. No relation was found between acuity and any refractive component. Genetic influences appear to predominate. Medians and ranges
Keywords: emmetropization • astigmatism • refractive error development