The effect of interrupted defocus on blur adaptation.

PURPOSE: Blur adaptation occurs when an observer is exposed to continuous defocus. However, it is unclear whether adaptation requires constant defocus, or whether the effect can still be achieved when the adaptation period is interrupted by short periods of clear vision. METHODS: The study included 12 emmetropes and 12 myopes. All observers wore full refractive correction throughout the experiment. 1D and 3D of myopic defocus was introduced using spherical convex lenses. An automated system was used to place the blurring lens before the RE for varying periods of blurred and clear vision during adaptation. Participants watched a DVD at 3 m during each 15 min trial. Visual acuity was measured using Test Chart 2000 before and after adaptation. RESULTS: Blur adaptation occurs to varying degrees depending on the periods of incremental blur exposure. Significant improvements in defocused visual acuity occur with continuous blur, equal blur and clear periods, as well as for longer blur periods. However, longer clear periods showed reduced adaptation and this trial is significantly different to the other three trials for both defocus levels (p < 0.001). No refractive group differences were observed for neither 1D nor 3D defocus (p = 0.58 and p = 0.19 respectively). CONCLUSIONS: Intervening periods of clear vision cause minimal disruption to improvements in defocused visual acuity after adaptation, indicating that blur adaptation is a robust phenomenon. However, when the exposure to clear vision exceeds the defocused periods, adaptation is inhibited. This gives insight into the effects of real-world tasks on adaptation to blur.

The time course of blur adaptation in emmetropes and myopes.

PURPOSE/BACKGROUND: This study examined the effect of myopic defocus on visual acuity (VA) over time, with attention being paid to the first point at which blur adaptation had a significant and measurable effect on defocused VA. Visual acuity was sampled at a higher rate than previous studies in order to assess the time course of blur adaptation processes in myopic and emmetropic observers. METHODS: Participants were 24 normally-sighted observers (12 emmetropes and 12 myopes, median age: 22.5 years). All ametropic participants wore their full refractive correction throughout the experiment. 1 D and 3 D of myopic defocus were introduced in two separate, randomised sessions. Visual acuity was measured using Test Chart 2000 at 2 min intervals over a 30 min session whilst looking through defocus lenses. Recovery clear VA was also measured every 2 min for a further 20 min. RESULTS: Defocused VA was found to improve significantly within 4 min after the introduction of defocus for both 1 D (P < 0.0001) and 3 D conditions (P < 0.0001). The improvements reached a plateau shortly after, with no significant further improvements in defocused VA after 6 min. There were no significant differences found in the temporal blur adaptation profiles between emmetropes and myopes (P = 0.267). Data were fitted with an exponential decay function; the lowest R(2) value for this fit was 0.95. CONCLUSIONS: Blur adaptation has a clinically significant and measurable effect on VA within 4 min of exposure to defocus. This finding indicates that the visual system instigates the neural compensatory mechanisms shortly after the appearance of defocus. Our results relate particularly to real-life vision of uncorrected myopes or myopes who remove their correction for part of the day.