Abstract

Purpose: Animal studies show that retinal defocus causes abnormal eye growth and myopia. Although some studies indicate larger blur detection thresholds in myopes, this finding is not consistent. We hypothesize that it is an impaired ability to discriminate blur (difficulty interpreting small changes in blur) and greater variability in their response to blur that is associated with myopia.

Methods: Continuous images (16deg diameter @ 40cm) of “dead leaves” stimuli were presented in four quadrants, each with a different level of Gaussian blur. Using a spatial 4AFC psychophysical paradigm, observers were required to decide which quadrant of the image was blurriest. For the blur discrimination condition, six different blur levels were used: 0.4, 0.8, 1.6, 3.4, 6.8 and 13.6 arc min.<br /> <br /> Thirty-seven young (22-31yrs) healthy adults participated, reliable psychophysical data was obtained for n=35 (n=21 myopes). Subjects had best corrected VA 0.0 LogMAR (20/20) or better in each eye and no binocular or accommodative dysfunction. Refractive error was determined by binocular subjective refraction that followed a vision screening and objective refraction. Subjects were classified into: Emmetropes (SE OU +0.50 to -0.25D); Myopes (SE -0.50 to -9.00D); or Hyperopes (SE +0.75 to +6.00D).

Results: No differences were found in the blur detection task between refractive groups (p=0.5) and there was no correlation between amount of refractive error and blur detection thresholds (R²=0.1, p=0.8). Blur discrimination thresholds were lower for myopes than emmetropes at discriminating for higher (≥1.6 arc min) levels of pedestal blur (p<0.05). There was a correlation between blur discrimination thresholds and amount of refractive error for those higher levels of pedestal blur (R²=0.32, p=0.05).

Conclusions: Contrary to our hypothesis, myopes were better than emmetropes at discriminating blur, and no different at detecting blur. These data suggests that myopes learn to discriminate blur and even when corrected their perception of blur is different than in emmetropes.