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L.S. Gray, N.C. Strang, D. Seidel, F. Brawley, K. Howard; Corneal Asphericity, Ocular Aberrations and Retinal Shape in Hyperopia, Myopia and Emmetropia . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5600.
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Purpose: Research examining differences in ocular components between refractive groups has mostly been confined to assessing parameters along the visual axis. However, recent work has suggested that off axis image quality may have a role in determining ocular shape and refractive error. The aim of the experiment was to determine whether any relationship exists between corneal asphericity, ocular aberrations and retinal shape in hyperopia, myopia and emmetropia. Methods: 20 hyperopic, 20 myopic and 20 emmetropic subjects participated with informed consent in the study. All groups were matched for age and all subjects had VA of 0.0 logMAR or better. Refractive error ranged from –7.25D to +6.50D spherical equivalent and cylindrical error was restricted to ≤2.00DC. Corneal topography was measured with the Orbscan, and whole eye aberration was assessed with the Zywave. Retinal shape was measured using the IOL Master at 5 degree intervals to 35 degrees eccentricity temporally and nasally along the horizontal meridian, while the subjects’ pupils were dilated using 2.5% Phenylephrine. Results: The hyperopic group had a significantly more negative Z(4,0) coefficient (spherical aberration, p=0.01) and significantly lower mean Z(3,3)/Z(3,–3) coefficients (trefoil, p=0.01) than the myopic group. Corneal asphericity was significantly less negative in the hyperopic group compared to the myopic group (p=0.05). Retinal curvature tended to be more spherical in the hyperopic and emmetropic groups compared to the myopic group, although a high level of intersubject variability was evident. Conclusions: Monochromatic aberrations and corneal shape show evidence of systematic variations with refractive error. Individual variation in retinal shape tends to predominate over refractive group differences. The present data shows no relationship between anterior and posterior characteristics of ocular shape.
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