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J. Cho, P. B. Kruger, L. R. Stark, T. Borgovan, S. Burke, M. Badar, R. Shah; Accommodation to Blurred Edges Viewed Through Off-Center Pinhole Pupils. Invest. Ophthalmol. Vis. Sci. 2007;48(13):970.
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At the margins of blurred edges, light arrives from one side of the pupil in myopic defocus, and from the opposite side in hyperopic defocus. We tested the hypothesis that the angle of incidence of light together with the spatial phase of the edge (dark/light or light/dark) can provide the sign of defocus for accommodation.
Subjects (22) viewed a vertical or horizontal luminance edge (544 nm) in a Badal optical system through a 0.75-mm pinhole pupil. The pinhole provided an open-loop condition and was positioned at the center of the subjects natural pupil, or off-center 1.5 mm left, right, up or down. The spatial phase of the target edge alternated between light/dark and dark/light at 0.2Hz during trials lasting 40.96 s, simulating square-wave changes in the sign of defocus. Blurred targets simulated 2D of defocus viewed through a 3-mm pupil. There were three pinhole pupil positions for the horizontal edge (up, down, center) and three for the vertical edge (left, right, center) giving six conditions overall. Accommodation was monitored continuously. There were 6 trials for each condition randomized in blocks. Gain and temporal phase-lag were calculated by FFT for each trial.
Group statistical analysis was performed with a randomization alternative to MANOVA. For the horizontal target, there was no significant difference between responses with the upward or downward displaced pupil (p = .67). For the vertical target, there was no significant difference in the response for leftward or rightward displaced pupil (p = .38). None of the combinations of target orientation and pupil displacement led to responses statistically different from the control with a centered pupil (Horizontal target: Pupil Up, p = .33; Pupil Down, p = .092; Vertical target: Pupil Left, p = .24; Pupil Right, p = .88). For single-case statistics, only one of the 44 tests (22 tests, by 2 tests per subject) was significant.
Accommodation did not respond to square-wave changes in edge spatial phase coupled with a fixed angle of incidence of light. Nevertheless, there are other mechanisms that the eye might use to extract the sign of defocus from the incident wavefront.
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