Abstract
Purpose :
Several factors impact myopia including genetics, peripheral retinal thinning, reduced choroidal thickness, time outdoor, dopamine concentration, and aberrations. The purpose of this study is to examine optical implications of different pupil sizes on aberrations and visual acuity by mimicking indoor and outdoor vision with numerical scaling of real-eye parameters of emmetropes from infant to adulthood and myopic development.
Methods :
Aberrations in the right eye of 5 healthy adult emmetropic subjects (equivalent sphere 0 to -1D) have been determined with dilated pupil using a Hartmann-Shack wavefront sensor (Thorlabs) and the axial length (22.5 to 23.8 mm) with an ultrasound device (Palmscan A-2000). Effective tri-dimensional point-spread functions have been calculated for different pupil apodizations (Matlab) using real-eye aberrations to mimic foveal and parafoveal vision for indoor and outdoor conditions. The impact of light distributions across the retinal layers have been analyzed with a volumetric absorption model of photoreceptors (Vohnsen et al. J. Vision 2017) and parameters scaled numerically from 18 (infant) to 30 mm (high myopic) axial length.
Results :
The analysis shows an optical scaling relation between pupil size, axial length, and retinal thickness. For emmetropes, an outdoor pupil size of 2 mm limits the solid angle of unaberrated rays to remain confined within photoreceptors. In turn, the obliqueness of rays reduces indoor visual acuity with a 6 mm pupil by one order of magnitude and even more with aberrations. Downscaling pupil size, axial length, and retinal thickness to match that of infant eyes shows that larger pupils are matched to shorter photoreceptors for the same visual acuity whereas for myopic eyes retinal thinning is the only possible optical response to increased light leakage across the retina.
Conclusions :
The study reveals an important optical relation between axial length and ray angles across the retina in relation to visual acuity which is highest when the angles of rays across the retinal photoreceptors is well-matched to the solid angle of the pupil. Larger pupils increase light leakage and thereby lower visual acuity. Thus, pupil size is intrinsically linked to emmetropization not due to aberrations alone but due to the obliqueness of the contributing rays as matched to the angular spread across the retinal thickness for highest visual acuity both for foveal and parafoveal vision.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.