Effect of blur adaptation on contrast discrimination in emmetropes and myopes

Abstract

Studies have investigated visual resolution and contrast detection following a period of degradation in the retinal image (blur adaptation) and have shown it can produce increases in visual resolution and changes in contrast sensitivity. However these studies only explored a limited range of spatial frequencies of sine wave gratings or tested visual resolution alone. The current study aimed to expand on previous work by investigating contrast discrimination and contrast threshold sensitivity before and after blur adaptation for a range of different spatial frequencies. In addition both myopes and emmetropes were tested to see if they responded in different ways to the blur adaptation. Contrast discrimination thresholds were measured (monocular) for a range of spatial frequencies of sine wave gratings (0.5 to 24 cycles per degree) before and after adaptation to +2D blur (45 minutes of adaptation) in four emmetropes and four myopes (mean refraction −6DS). The contrast pedestal was set to 10% and an adaptive 2AFC procedure was employed. Contrast sensitivity and high contrast visual acuity were also measured before and after adaptation. The results showed increases in contrast sensitivity and contrast discrimination at some spatial frequencies after adaptation while others were reduced. In particular, the myopes showed the largest increases in mid to high spatial frequencies (16–20 cycles per degree) while emmetropes displayed reduced sensitivity at the higher spatial frequencies (18–24 cycles per degree). Measurements of the optics before and after adaptation ruled out any optical changes being responsible. The results therefore point to different neural adaptation strategies in the refractive groups. Possible models of how the visual system responds to periods of blur are discussed.

NSF BCS-0715076, NIH EY017678.