Abstract
Purpose: :
Adaptation to blurred images makes images appear relatively sharper and adaptation to clear images has the opposite effect. Compared to emmetropes, myopes have been shown to exhibit better visual performance with blurred stimuli and greater adaptation to blur. The aim of this study is to determine if differences exist between stable myopes’ and emmetropes’ blur detection thresholds at baseline and following adaptation to blurred and clear text.
Methods: :
21 stable myopes (mean±sd: -4.38±2.28 D) and 15 emmetropes (mean±sd: 0.23±0.33D) aged 22-34 years were best corrected and viewed a passage of text on a computer monitor at 33 cm in order to measure: (1) baseline blur detection thresholds and (2) thresholds after adaptation to blurred or clear text. Blurring of the stimulus text was generated by the application of a pseudo-Gaussian filter. A double randomized staircase procedure was used to determine blur thresholds. The order of blur and clear adaptation was random. Descriptive statistics and t-tests for differences between conditions and refractive groups were used.
Results: :
Stable myopes and emmetropes had similar thresholds at baseline (mean±sd for myo vs emm: 0.47±0.10 vs 0.49±0.06), but higher myopia was correlated to lower thresholds (R=0.34;p<0.05). Myopes and emmetropes had similar thresholds after blur adaptation (mean±sd for myo vs emm: 0.07±0.10 vs 0.03±0.07; p=0.12) and clear adaptation (mean±sd for myo vs emm: -0.27±0.08 vs -0.27±0.06; p=0.93). Blur thresholds changed significantly more from baseline following clear adaptation compared to blur adaptation (p<0.005).
Conclusions: :
Blur detection thresholds before and after adaptation to blurred or clear text is similar between stable myopes and emmetropes. However, higher stable myopia is related to lower thresholds at baseline. Adaptation to clear images appears to be more robust than adaptation to blurred images, regardless of refractive error.
Keywords: myopia • refraction