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E. Gambra, J. Yuan, Y. Wang, S. Marcos, P. B. Kruger; Dynamic Accommodation With High Order Aberrations Blurred Simulated Targets. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4293.
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© ARVO (1962-2015); The Authors (2016-present)
High order aberrations (HOA) have been suggested to play a role in accommodation. They may serve as a cue to determine best focus direction. Alternatively, blur induced by aberrations may impair accommodative response. We studied how blur induced by HOA affects the dynamic accommodation response.
The stimulus was a high contrast monochromatic (550 nm, 10-nm bandwidth, 20cd/m2) Maltese cross subtending 1 deg and viewed through a 3mm-artficial pupil in a Badal optometer. Eight additional blurred targets, simulating 0.3 µm and 1 µm of defocus, vertical coma, vertical trefoil and spherical aberration respectively were calculated in Matlab for a 3-mm pupil, and presented as stimuli using a video projector. Accommodation stimulus followed a 0.2 Hz sinusoid of ±1 D amplitude on a 2 D base level during 41-sec. trials. The accommodation response was measured at 100 Hz. Three undilated subjects were tested (age: 27.0±4.6; sphere: 0.3±1.4 D; cylinder: -0.58±0.29 D; HOA= 0.17±0.08 µm for a 3-mm pupil). Sphere and cylinder were corrected with trial lenses. Two additional subjects were tested but discarded as they did not respond or showed a great variability across trials. Each of the nine experimental conditions was repeated 6 times.Fourier analysis of the response was performed to calculate its amplitude and phase at 0.2 Hz. The accommodation gain was defined as the response amplitude /demand. ANOVA was performed to assess significant differences across conditions.
Average gain for non-aberrated condition was 0.7±0.4. On average, gain decreased by 19% for targets blurred with 0.3 µm of defocus, coma and spherical aberration, and by 2% with trefoil, but those changes were not statistically significant (p>0.4). For targets blurred with 1µm, gain decreased by 27%, 42%, 50% and 71% for coma, trefoil, defocus and spherical aberration respectively (p<0.05 in all cases). In general, lower gain responses were also more delayed but the differences were not statistically significant. Individually, gains varied across subjects, but in all cases the responses to targets blurred with the higher amounts of aberrations resulted in a statistically significant decrease of gain.
Target blur induced by HOA impairs dynamic accommodation, proportionally to the amount of blur. The largest effect occurs for symmetric aberrations. However, the effects are only significant for amounts of aberrations higher than typical values, suggesting that for normal amounts of aberrations blur induced by high order aberrations is not greatly impairing the accommodation response.
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