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S. Pardhan, S. Rae; Variation of Naso-Temporal Asymmetry of the Peripheral Refractive Error in Myopes and Emmetropes and the Relationship With Defocus During Near Work. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3943.
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It is known that the peripheral field of myopes is hyperopic. What is less well established is how this is affected by the magnitude of the refractive error and whether there are variations in nasal-temporal asymmetry. Our previous work has investigated this for distance viewing and this study investigates the potential impact of the pattern of peripheral refraction during near work in myopes and emmetropes.
Refractive error was assessed at peripheral retinal locations in 35 subjects, using the Shin Nippon SRW5000 auto-refractor. Measurements were obtained for central and 5, 10, 15, 20 and 30° eccentricity in nasal and temporal retinas. Subjects were divided into four refractive error groups: Group1: emmetropic; Group2: <4.00DS; Group3, 4.25 to 6.25 DS, Group4, >6.50DS. The spherical equivalent, J180 astigmatism, sagittal and tangential power components were calculated, normalised to central refraction. Accommodative lag was measured for a target at 1/3m and the peripheral refractive error was recalculated to indicate the pattern of spherical equivalent, sagittal and tangential power components in nasal and temporal retina during near work.
Both nasal and temporal retinal locations differed significantly between refractive error groups (p < 0.05) with emmetropes showing relatively myopic peripheries and myopes relatively hyperopic peripheries. Only temporal retinal locations were correlated with refractive error (Pearson: r = -0.633, p < 0.001). Accommodative lag in emmetropes resulted in a central hyperopic error but the relative peripheral myopia showed a reduction of the magnitude of the defocus when moving away from the fovea. A reverse of this pattern was shown in low and moderate myopes with foveal hyperopia which further increased in the periphery.
The pattern of peripheral refraction may increase or decrease the defocus resulting from accommodative lag during near work. Data show an increased hyperopic pattern in myopes compared to distance vision and compared to emmetropes. Accommodative lag could act as a protective mechanism in emmetropic individuals with relatively myopic peripheries. Pardhan, Rae. 12th International Myopia conference, July 2008. Cairns
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