Abstract
Purpose :
To investigate the effect of optically imposing astigmatic blur on meridional contrast sensitivity function.
Methods :
Non-astigmatic young adults (age range, 18-30 yrs; n = 18) with corrected-to-normal visual acuity (logMAR −0.1 or better) participated. Contrast sensitivities for horizontal and vertical gratings (spatial frequencies: 1 to 8 cycles per degree) were measured before and after adapting to either +3.00 D with-the-rule (WTR) astigmatism or +3.00 D against-the-rule (ATR) astigmatism. With the use of spectacle trial lenses to optically impose the simple myopic astigmatism, the retinal image quality was substantially blurred along the power meridian (WTR: horizontal gratings; ATR: vertical gratings), leaving the perpendicular axis meridian largely unaffected. A “top-up adapt-test” paradigm was adopted to minimize the decay of the adaptation effect. During the blur adaptation process, participants were briefly presented with natural scene images (first testing trial, 10 min; each subsequent testing trial, 6 sec), followed by post-adaptation contrast sensitivity function testing for horizontal and vertical gratings. Meridional anisotropy in contrast sensitivity was computed to characterize the contrast sensitivity difference between the two grating orientations.
Results :
Astigmatism adaptation enhanced contrast sensitivity at the blurred power meridian but reduced contrast sensitivity at the unaffected axis meridian. In the WTR condition, contrast sensitivity for horizontal gratings was significantly increased compared to the baseline (p < 0.001), while contrast sensitivity for vertical gratings was found to be significantly decreased (p = 0.003). Likewise, in the ATR condition, contrast sensitivity for vertical gratings was significantly increased (p < 0.001), and that for horizontal gratings was significantly decreased (p = 0.03). These two factors combined together caused a significant decrease in meridional anisotropy of contrast sensitivity in both astigmatism conditions (p < 0.001).
Conclusions :
Here we show that astigmatism adaptation occurs in natural scene viewing. The brief astigmatism adaptation increased contrast sensitivity at the blurred power meridian but decreased contrast sensitivity at the unblurred axis meridian. Importantly, these findings suggest that the mature visual system possesses the functional plasticity to recalibrate during astigmatism adaptation.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.