Increased accommodation following adaptation to image blur in myopes.

Prolonged exposure to blurred images produces perceptual adaptation (M. A. Webster, M. A., Georgeson, & S. M. Webster, 2002). The purpose of this study is to test whether in addition to the reported change in perceived blur there is also a change in accommodation. Young adult (aged 18 to 31 years) myopic (n = 23) and emmetropic (n = 17) subjects participated in the study. Myopes were tested with contact lenses and had corrected monocular visual acuity of 20/20 or better. Accommodation was measured binocularly with a PowerRefractor, an eccentric infrared photorefractor. Accommodation for a near target (high-contrast text at 0.33 m) was measured for 2 min before and immediately after 3 min of blur exposure. Blur was induced using 0.2 Bangerter diffusing filters in front of both eyes. In addition, accommodation was measured for a far target (high-contrast letters at 4.0 m) before and after the near measurements, with each subject's initial far readings used as a baseline for calculating the accommodative responses at near. Compared to the pre-adaptation level, myopes showed a significant (p < .01) increase in the near accommodative response after 3 min of blur adaptation, while accommodation to the near target in emmetropes did not change. In a second experiment using monocular viewing, the increase of accommodation found in myopes was shown to occur during the period of blur exposure. The refractive group differences in the accommodative response may be related to differences in the habitual response to image clarity between myopes and emmetropes under normal viewing conditions.