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S Marcos, S Barbero, L Llorente; The Sources Of Optical Aberrations In Myopic Eyes . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1510.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:1) To determine the sources of aberration in myopic eyes, by measuring in vivo the optical quality of the cornea and of the internal ocular components as a function of myopia. 2) To relate measured aberrations to physical properties of myopic eyes, using eye models. Methods:Experiments were done on 49 young eyes with spherical error ranging from -0.25 to -15 D. Total aberrations were measured with Laser Ray Tracing. The pupil was sampled sequentially and the corresponding images collected on a CCD camera. Ray aberrations were computed from the image deviations from a reference. Corneal aberrations were obtained from videokeratographic corneal elevation maps. Pupil size was 6.5 mm. Wave aberrations were described as Zernike polynomial expansions. Root Mean Square wavefront error (RMS) was used as optical quality metric. The wave aberration for the internal optics was the difference of total and corneal wave aberrations. Results:1) Total RMS (for 3rd order and higher aberrations) increased significantly with myopia (p<0.001, slope=-0.085 µm/D, respectively). Corneal and internal aberrations also increased significantly (p<0.049 and p=0.0022), but with lower rates (slope=-0.036 and -0.058 µm/D). 2) Third order aberrations increased significantly for both components. For lower myopes (<6 D) some balance of corneal by internal aberration occurs, whereas for higher myopes individual aberrations add up. 3) As myopia increased, corneal spherical aberration increased significantly (p=0.001) toward more positive values and internal spherical aberration (p=0.009) changed toward more negative values, keeping total spherical aberration constant and low along the entire range. 4) The increase of corneal spherical aberration is due to increased corneal asphericity. Simulations using eye models show that the increase of negative internal spherical aberration is consistent with flattening of the crystalline lens posterior surface. Both properties have been reported for myopes. 5) Pupil decentration could cause a common increase of corneal and internal coma, whereas crystalline lens tilt may produce changes in the degree of balance. Conclusion: 1) Degraded retinal image quality occurs in high myopia. Could image degradation imposed by aberrations contribute to disrupt emmetropization?. 2) The increase of aberrations in myopia can be explained by physical properties of the ocular components. 3) While some compensatory interactions of ocular components are lost in high myopia, balance still occurs for spherical aberration.
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