Abstract
Abstract: :
Purpose: Previous studies have reported a higher number of retinal vessels at the optic disc of people with Down syndrome (DS) (Williams et al, 1973). Other than commenting on a ‘rosy’ appearance, no studies have documented the characteristics of the disc itself in DS. Here we present quantitative information on the vessels and the disc dimensions in children with DS, and in control children matched for axial length. Methods: The children with DS, aged 6–15 years, are members of a longitudinal study group. Control children, aged 4–15 years are recruited from patients attending the University Clinic, and through staff of the University. Axial length is measured by IOLMaster, a non–contact instrument. Refractive error is assessed by Mohindra retinoscopy and defined as mean sphere. Fundus photography is carried out with the Topcon non–mydriatic TRC–NW6S. Vessels crossing the disc margin (Elschnig rim) are counted manually. Area of the disc is assessed by the Imagenet 2000 software. Both measurements are made by a researcher masked as to which subject group the child belongs. Results: To date, 16 eyes have been identified in children with DS which have matched controls (identical axial length within 0.25mm). Mean axial length in DS is 21.45±1.05 mm and in controls 21.74±1.07 mm. Range of mean sphere in DS is –1.25D to +9.38D and in controls –0.25D to +11.38D. Mean number of vessels crossing the disc margin is 15 in DS and 11 in controls. Relative mean area of the disc is 4.453 ±1.189 units in children with DS and 3.726± 0.497 units in controls (t=2.258, df=30, p=0.031). Conclusions: We confirm the increased number of blood vessels emerging from the optic disc in children with DS. The finding that the optic disc is larger in children with DS is unexpected. Visual acuity is poorer in DS than controls (John et al 2004), which could argue for fewer ganglion cells and therefore predict a smaller optic disc (Fierson, 1990). The implications of a greater number of vessels emerging from a larger optic disc are as yet unclear, but the morphology of the optic disc is clearly different in DS.
Keywords: optic disc • blood supply • imaging/image analysis: clinical