Specifying peripheral aberrations in visual science

Abstract

Abstract. Purpose: Investigations of foveal aberrations assume circular pupils. However, the pupil becomes increasingly elliptical with increase in visual field eccentricity. We address this and other issues concerning peripheral aberration specification. Methods: One approach uses an elliptical pupil similar to the actual pupil shape, stretched along its minor axis to become a circle so that Zernike circular aberration polynomials may be used. Another approach uses a circular pupil whose diameter matches either the larger or smaller dimension of the elliptical pupil. Pictorial presentation of aberrations, influence of wavelength on aberrations, sign differences between aberrations for fellow eyes, and referencing position to either the visual field or the retina are considered. Results: Examples show differences between the two approaches. Each has its advantages and disadvantages, but there are ways to compensate for most disadvantages. Two representations of data are pupil aberration maps at each position in the visual field and maps showing the variation in individual aberration coefficients across the field. Conclusions: Based on simplicity of use, adequacy of approximation, possible departures of off-axis pupils from ellipticity, and ease of understanding by clinicians, the circular pupil approach is preferable to the stretched elliptical approach for studies involving field angles up to 30 deg.

IMI – Clinical Myopia Control Trials and Instrumentation Report

“…240 Based on simplicity of approach, possible departures of off-axis pupils from ellipticity and ease of understanding, a circular pupil approach based on a diameter that fits within the actual pupil should be adopted. 231,270 Alternatively, as this approach may bias the results to the central optics-of possible importance when measuring through center-surround zonal lenses-Zernike fitting could be avoided all together by either determining refractive power based on the local slope/zonal integration 271 or by calculating the wavefront vergence based on the raw slope measured by the instrument. 272 Charman and colleagues 270 argued that visual field (such as superior visual field) rather than a retinal (such as inferior retina) reference be used when describing peripheral refraction measures.…”

Effect of Pupil Size on Wavefront Refraction during Orthokeratology

“…Such stretching affects all the Zernike coefficients. 23 Recently, Zernike-like orthogonal polynomials were proposed for Nevertheless, here we were mainly interested in computing the refractive error, so we used the equations provided by Atchison et al 24 truncated at 2 nd order for Zernike refraction and up to 6 th order for Paraxial refraction. We implemented an improvement which may be important for large field angles due to pupil aberrations:…”

Theoretical model of the contributions of corneal asphericity and anterior chamber depth to peripheral wavefront aberrations

“…In this model, peripheral spherical equivalent error was calculated from peripheral Zernike defocus, which was derived from a stretched circular exit pupil . The peripheral spherical equivalent error is just a rough approximation of the spherical equivalent error for a real elliptical pupil, especially when eccentricity is >30° . In addition, the image plane determined by the spherical equivalent error doesn't necessarily coincide with the optimal image plane due to the influence from other higher order aberrations on the image quality .…”

“…35,36 The peripheral spherical equivalent error is just a rough approximation of the spherical equivalent error for a real elliptical pupil, especially when eccentricity is >30°. 37 In addition, the image plane determined by the spherical equivalent error doesn't necessarily coincide with the optimal image plane due to the influence from other higher order aberrations on the image quality. 38 In this study, the exact location of best image in the periphery was not modelled.…”