The Optical Contribution to the Human Contrast Sensitivity Function Peak Shift With Changing Luminance

Abstract

Purpose : It has been known that as luminance is increased, the peak of the contrast sensitivity function (CSF) is shifted from lower to higher spatial frequencies. However, this shift may not be fully explained by the luminance change alone. The goal of this study is to determine if the eye’s aberrations also influence this peak shift. To this end, we measured subjects at three different luminance levels under two different optical conditions (with and without adaptive optics (AO) aberration correction).

Methods : An AO vision simulator was used to correct the aberrations of three healthy subjects while they performed psychophysical tasks displayed through the system by a projector. The CSF of each subject was measured using the qCSF method, both with and without AO correction of higher order aberrations (HOA), at three different luminance levels, 0.05, 5, and 500 cd/m². For conditions without AO, the subjects’ defocus and astigmatism were kept well corrected using a Badal and a phoropter. Subject accommodation was paralyzed with 1% tropicamide. Visual benefit of correcting HOA was quantified by the ratio (CSF with AO:CSF without AO). Data are presented as mean±SD.

Results : For both with and without AO correction, a peak shift of the CSF from lower to higher spatial frequencies was observed as luminance was increased. Correction of HOA further shifted the mean CSF peak by 0.61±0.41 and 0.41±0.42 cyc/deg at 0.05 and 500 cd/m², respectively, compared to the uncorrected measurement at the same luminance. A larger peak shift of 1.72±0.60 was observed with AO correction for the 5 cd/m² condition. Overall, visual benefit from AO correction was increased with increasing spatial frequency for all luminance levels. The mean visual benefit from 2 to 5 cyc/deg at the lowest luminance of 0.05 cd/m² (1.75±0.55) was considerably larger than at 5 and 500 cd/m² (1.16±0.08, and 1.10±0.05).

Conclusions : AO benefit showed a dependency on luminance and spatial frequency with greater AO benefit observed for higher spatial frequencies and lower luminances. The CSF peak shift that is observed as luminance is increased may be partially due to optics, rather than solely dependent on luminance. Interestingly, the CSF peak shift was consistently greatest at 5 cd/m² for all subjects. Therefore, the relationship between whether optics or luminance dominates this peak shift may change as a function of luminance.

This is a 2020 ARVO Annual Meeting abstract.