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Norberto Lopez-Gil, Paula Bernal-Molina, Richard Legras, Teresa Ferrer-Blasco, Robert Montés-Micó, Ciencias de la Visión; Depth-of-focus of the accommodating eye. Invest. Ophthalmol. Vis. Sci. 2013;54(15):384.
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To obtain experimental values of the depth-of-focus (DoF) of the human eye for different accommodative states.
In a first part of the experiment we measured the aberrations of 7 young eyes (29.7 ± 7.7 years) during accommodation at 8 different accommodative steps (from -1 to 6 D). Then, in a second part, accommodation was paralyzed (cyclopentolate) and we used an adaptive optics system with a deformable mirror (Imagine Eyes, France) to correct the aberrations of the paralyzed eye and to simulate the aberrations of the accommodated eye for each accommodative state measured in the first part of the experiment. A Badal system was used to modify the vergence of the stimulus in order to obtain three-repeated measurements of the subjective DoF. Equally in the second part of the experiment, an artificial pupil with a similar diameter to the natural pupil measured in the first part was used. The object stimulus used consisted on microdisplay showing three lines of high contrast black letters of 0.4, 0.5 and 0.6 VA on a white background. The criteria used for DoF was the objectionable blur.
All subjects presented a similar result of DoF (maximum intra-subject SD = 0.23 D) with a mean value of DoF which increased from 0.85 to 1.07 D during accommodation (0 to 6 D). This increase can be explained in terms of pupil accommodative myosis (mean pupil diameter decreased from 5.70 to 4.63 mm during the accommodation range). Accommodative lag increased with accommodation, and for large accommodation demands (4-6 D) the refractive state of the eye was close to the extreme of the DoF, so, in fact, accommodation was minimum. Results of DoF correlate with the few measurements previously obtained using other methodologies by other authors.
Under experimental conditions, DoF is close to 1 D. Our results clearly indicate that, if the deterioration of the retinal image quality is acceptable, the visual system uses DoF to accommodate less, and thus presents a real accommodative lag for near targets.
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