Wavefront Aberrations Due to a Gaussian Model of Foveal Edema

Abstract

Purpose: : The presence of foveal edema can degrade the optical performance of the eye by introducing increased wavefront aberrations (WA). The purpose of this study was to simulate the type and level of WA caused by a convex vitreoretinal interface (CVRI) due to foveal edema.

Methods: : A modified Navarro eye model was incorporated into a ZEMAX model of a Shack-Hartmann wavefront sensor. The CVRI was represented by a Gaussian function (σ=106 µm). The incoming rays were partially diffusively reflected and partially refracted by the VRI. The rays were focused on the photoreceptor layer and diffusively reflected. The outgoing rays were again refracted by the VRI before exiting the eye. WA were simulated as a function of the CVRI maximum peak height (250 to 400 µm from photoreceptor cell layer), eccentricity with respect to peak (0 to 350 µm), and retinal refractive index (1.36 to 1.47). Lower order aberrations (LOA) (2^nd) and higher order aberrations (HOA) (3^rd - 7^th) were represented by Zernike polynomials.

Results: : The incident rays reflected from the VRI primarily introduced LOA of defocus which was maximum at the CVRI peak and decreased in the periphery. The outgoing rays refracted by the VRI generated both LOA and HOA. A 60% increase (250 to 400 µm) in the CVRI peak height resulted in 9 and 16 fold increases in LOA and HOA root mean square (RMS) errors, respectively. Symmetrical aberrations were largest at the CVRI peak and decreased in the periphery. Asymmetrical aberrations were negligible at the CVRI peak. Astigmatism, trefoil, and terafoil were largest at the eccentricity of 100 µm, while coma and 2nd order astigmatism were largest at the eccentricity of 67 µm. An 8% increase in the refractive index of the retina resulted in 6 and 8 fold increases in LOA and HOA RMS, respectively.

Conclusions: : Symmetrical aberrations were primarily present at the CVRI peak, while asymmetrical aberrations were more pronounced in the periphery. The magnitude of aberrations was dependent on the peak height of the CVRI and refractive index of the retina. This model may be applied for estimating the type and level of aberrations in patients with foveal edema.

Keywords: aberrations • edema • macula/fovea