The Effect of Blur Adaptation on Contrast Sensitivity

Abstract

Abstract: : Purpose: Blur sensitivity and blur driven accommodation have been shown to be reduced in myopic children. However, recent studies indicate that myopes exposed to prolonged periods of uncorrected vision seem to exhibit improvement in visual resolution due to blur adaptation. The purpose of this study is to examine the effect of different conditions of myopic blur on contrast sensitivity function after adaptation to a natural scene. Methods: Contrast sensitivity function was meaasured in 10 emmetropic subjects after adaptation to a natural scene whose amplitude spectrum had a slope of –1.0. All measurements were made monocularly on the right eye. The effects of blur adaptation were measured under five different conditions: a zero contrast adapting field with in–focus (clear) test bars (baseline); clear adapting scene and clear test bars (CACB); clear adapting scene and blurred test bars (CABB); blurred adapting scene and clear test bars (BACB); and blurred adapting scene and blurred test bars (BABB). All conditions except for the baseline condition had an initial 15 min adaptation period. There was also a 10 second re–adaptation period between consecutive trials for all the conditions except for baseline condition that had a 3 second re–adaptation period. Threshold contrast was estimated using a QUEST procedure at 9 spatial frequencies between 0.24 and 30 cpd. Results:Compared to baseline, the CACB condition resulted in a statistically significant reduction in sensitivities of 0.23–0.65 log units at low and mid–spatial frequencies between 0.47 and 7.6 cpd (p<0.007). Compared to CACB, blur adaptation in the BACB condition resulted in an increase in sensitivity of 0.25 log units at 1.9 cpd (p=0.009) with no effect at higher spatial frequencies. The effect of blur adaptation was also studied by comparing CABB to constant blur in the BABB condition that exhibited an increase in sensitivity of 0.16 log units at 15.13 c/deg (p=0.025). Conclusions: These results demonstrate contrast sensitivity changes following adaptation to different blurred natural scene conditions. atural scene viewing results in a low frequency bias and that contrast adaptation plays a role in everyday viewing. The effect of blur adaptation has shown an increase in sensitivity at the highest spatial frequency, thus hinting at the possibility of improvement in visual resolution following prolonged periods of blur. We have thus speculated that if blur adaptation increases sensitivity at high spatial frequencies then it will prove to be a good stimulus for accommodation and hence will decrease accommodative lag, a putative risk factor for myopia progression.

Keywords: adaptation: blur • contrast sensitivity • myopia