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Antonio J. Del Águila-Carrasco, Iván Marín-Franch, Paula Bernal-Molina, José J. Esteve-Taboada, Philip B. Kruger, Robert Montés-Micó, Norberto López-Gil; Accommodation Responds to Optical Vergence and Not Defocus Blur Alone. Invest. Ophthalmol. Vis. Sci. 2017;58(3):1758-1763. doi: 10.1167/iovs.16-21280.
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To determine whether changes in wavefront spherical curvature (optical vergence) are a directional cue for accommodation.
Nine subjects participated in this experiment. The accommodation response to a monochromatic target was measured continuously with a custom-made adaptive optics system while astigmatism and higher-order aberrations were corrected in real time. There were two experimental open-loop conditions: vergence-driven condition, where the deformable mirror provided sinusoidal changes in defocus at the retina between −1 and +1 diopters (D) at 0.2 Hz; and blur-driven condition, in which the level of defocus at the retina was always 0 D, but a sinusoidal defocus blur between −1 and +1 D at 0.2 Hz was simulated in the target. Right before the beginning of each trial, the target was moved to an accommodative demand of 2 D.
Eight out of nine subjects showed sinusoidal responses for the vergence-driven condition but not for the blur-driven condition. Their average (±SD) gain for the vergence-driven condition was 0.50 (±0.28). For the blur-driven condition, average gain was much smaller at 0.07 (±0.03). The ninth subject showed little to no response for both conditions, with average gain <0.08. Vergence-driven condition gain was significantly different from blur-driven condition gain (P = 0.004).
Accommodation responds to optical vergence, even without feedback, and not to changes in defocus blur alone. These results suggest the presence of a retinal mechanism that provides a directional cue for accommodation from optical vergence.
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