Effects of refraction on straylight

Abstract

AbstractThe effect of cataract and other media opacities on functional vision is typically assessed clinically using visual acuity. However, from both clinical and basic research, it has become evident that straylight (the functional result of light scattering in the eye) must be considered also as significant part of quality of vision. The optical basis of acuity and scatter are quite different. Acuity (and contrast sensitivity) depend on the refractile structure of the eye optics (refractive error and aberrations), whereas straylight mostly depends on the presence of light scattering particles of microscopic size. It must be noted that the first aspect is of global nature; the refractile structure concerns all light entering the pupil, whereas light scattering is of local nature, concerning only part of the light entering the pupil. The other part is under the influence of the refractile structure only. The subject of this presentation is the potential link between these two phenomena, and their functional counterparts: is visual acuity in cataract and other media opacities related to straylight? On the other hand, is straylight or its measurement under the influence of refractile errors, more in particular for myopic eyes?Potential interdependence between acuity and straylight was addressed for normal eyes by manipulating refractive correction with plus lenses. No effect on measured straylight values was found. Also statistically, little relation between straylight and acuity exists in the normal population, in concordance with expectation from theoretical modelling. Visual acuity losses with cataract and other media opacities are not due to straylight, but caused by aberrations and micro‐aberrations. Straylight defines disability glare, and causes symptoms of glare, haloes, hazy vision etc. Overall, visual acuity and straylight are rather independent aspects of quality of vision.For myopic eyes, literature has shown a clear interdependence (Rozema et al. IOVS 2010 pp 2795–2799). To understand this finding, straylight values were measured with the C‐Quant (Oculus Optikgeräte, GmbH, Wetzlar, Germany) in (1) near‐emmetropic eyes (n = 30) with various negative powered refractive lenses and in (2) myopic eyes (n = 30) corrected with prescribed eyeglasses and contact lenses. The straylight measurements in each group were compared in the different conditions. In the near‐emmetropic group, a significant effect (p < 0.001) of each added negative diopter was found to increase straylight values with 0.006 log‐units. In the second group, no significant correlation with type of correcting lens was found on straylight values. So, refractive correction with high minus power (contact) lenses result in subtle increase of straylight values. These changes are relatively small though.