Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians (Optometrists) · 2014
Theoretical model of the contributions of corneal asphericity and anterior chamber depth to peripheral wavefront aberrations.
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He Ji C
Аннотация
PURPOSE: The purpose of this study was to theoretically model the contributions of corneal asphericity (Q) and anterior chamber depth to peripheral wavefront aberrations.
METHODS: Ray-tracing was performed on a model eye using a customised MatLab program to calculate Zernike aberrations up to the 5th order across ±60° of the horizontal visual field. The corneal Q was varied from -0.5 to 0.8, and the anterior chamber depth was changed from 2.05 to 4.05 mm while axial length was held constant. Spherical equivalent refractive error derived from Zernike defocus was used to estimate peripheral refraction.
RESULTS: Relative to axial Zernike aberrations, both defocus and astigmatism in the peripheral field increased with the corneal Q value, but the increases in relative peripheral astigmatism were much smaller in amplitude than relative peripheral defocus. Anterior chamber depth shortening caused the relative peripheral defocus and astigmatism to increase toward more positive values, although the changes in relative peripheral astigmatism with anterior chamber depth were small. Combination of the variations in both corneal Q and anterior chamber depth does not produce linear sum of the changes in relative peripheral defocus. The relative peripheral refractive error was more myopic when either the corneal Q was increased or the anterior chamber depth was shortened. The changes in relative peripheral x-axis coma, trefoil and spherical aberration with corneal Q value were complex but were barely changed with anterior chamber depth within the central 60° visual field.
CONCLUSIONS: Both corneal asphericity and anterior chamber depth play important roles in determining peripheral wavefront aberrations. The two factors nonlinearly interact to affect peripheral aberrations. Higher corneal Q and/or shorter anterior chamber depth tend to produce relatively more myopic peripheral refraction. Increasing the Q value of the anterior surface of a contact lens might provide an interesting intervention to slow myopia progression.
METHODS: Ray-tracing was performed on a model eye using a customised MatLab program to calculate Zernike aberrations up to the 5th order across ±60° of the horizontal visual field. The corneal Q was varied from -0.5 to 0.8, and the anterior chamber depth was changed from 2.05 to 4.05 mm while axial length was held constant. Spherical equivalent refractive error derived from Zernike defocus was used to estimate peripheral refraction.
RESULTS: Relative to axial Zernike aberrations, both defocus and astigmatism in the peripheral field increased with the corneal Q value, but the increases in relative peripheral astigmatism were much smaller in amplitude than relative peripheral defocus. Anterior chamber depth shortening caused the relative peripheral defocus and astigmatism to increase toward more positive values, although the changes in relative peripheral astigmatism with anterior chamber depth were small. Combination of the variations in both corneal Q and anterior chamber depth does not produce linear sum of the changes in relative peripheral defocus. The relative peripheral refractive error was more myopic when either the corneal Q was increased or the anterior chamber depth was shortened. The changes in relative peripheral x-axis coma, trefoil and spherical aberration with corneal Q value were complex but were barely changed with anterior chamber depth within the central 60° visual field.
CONCLUSIONS: Both corneal asphericity and anterior chamber depth play important roles in determining peripheral wavefront aberrations. The two factors nonlinearly interact to affect peripheral aberrations. Higher corneal Q and/or shorter anterior chamber depth tend to produce relatively more myopic peripheral refraction. Increasing the Q value of the anterior surface of a contact lens might provide an interesting intervention to slow myopia progression.