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Norberto Lopez-Gil, Ivan Marín-Franch, Paula Bernal-Molina, Jose Esteve-Taboada, Robert Montés-Micó, Philip B Kruger, Antonio Del Águila-Carrasco; Does accommodation respond equally to artificially blurred as to real out-of-focus retinal images?. Invest. Ophthalmol. Vis. Sci. 2017;58(8):321.
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© ARVO (1962-2015); The Authors (2016-present)
To determine whether accommodation is driven by the presence of an accommodation error (image focused in front or behind the retina) or just by the presence of defocus blur in the retinal image, since both are potential cues that could trigger accommodation.
A custom-made adaptive optics system with a deformable mirror together with a 4-mm artificial pupil was used to measure the monocular accommodation response of nine subjects to a monochromatic (550 ± 5 nm) Maltese-cross target. Two conditions, vergence-driven condition and blur-driven condition, were tested against each other. In the vergence-driven condition, the accommodative demand changed sinusoidally between −1 and −3 D at 0.2 Hz producing changes in defocus blur on the retina that accompanied changes in optical vergence. In the blur-driven condition, the image was always projected in-focus on the retina so there was no accommodative error, but the target itself, presented on a microdisplay, blurred and cleared sinusoidally over time due to computer-generated blur. In both conditions, the accommodation feedback loop was open because defocus, astigmatism, and higher-order aberrations of the eye were removed at 20 Hz with the adaptive optics system. Six trials of 20 s of duration were performed for both conditions, presented in a random order.
The accommodative response was different in the two conditions for all subjects except one, who did not respond in either of the conditions. On average, in the vergence-driven condition subjects followed the sinusoidal change in stimulus-vergence with a clear sinusoidal change in their refractive state (1.00±0.56 D), but presented a very small refractive change (0.14±0.06 D) in the blur-driven condition, similar to the small microfluctuations of accommodation. The difference in accommodative response between the two conditions was significant (p<0.004).
Accommodation responds to the sign of defocus (lead or lag of accommodation) and not just to the blur generated when the image is not in-focus on the retina. These results suggest the presence of a retinal mechanism that provides a directional cue for accommodation from optical vergence.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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