Retinal straylight as a function of age and ocular biometry in healthy eyes.

PURPOSE To determine the dependency of straylight on ocular biometry. METHODS This prospective study included 518 eyes of 277 volunteers of diverse ethnic backgrounds with healthy eyes of various iris colors. The eyes had retinal straylight tested using a commercial psychophysical device. Ocular axial length and refraction were also measured with an ocular biometer and an autorefractometer, respectively. RESULTS The measured retinal straylight was validated by comparing data with the age model described in the literature as log(s) = P(1) + log[1 + (age/65)(4)], where P(1) is the logarithm of the average straylight for the eyes of a newborn. The data agreed well with this model, although P(1) was slightly higher (0.931 vs. 0.87). When this model was subtracted from the measured straylight values, a quadratic increase was found in the function of axial length, L: log(s) = 0.931 + log[1 + (age/65)(4)] + (0.01089L(2) - 0.4820L + 5.330). A similar model was defined for the spherical equivalent refraction SE. This corresponds to an increasing amount of straylight for increasing degrees of myopia. No correlation was found with keratometry and corneal astigmatism or with iris color. CONCLUSIONS Retinal straylight increases not only with age, but also with axial length. Further study is needed to identify the cause of this dependency.