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First Author: P.Bernal-Molina SPAIN
Co Author(s): J. Villa R. Legras T. Ferrer-Blasco R. Montés-Micó E. Usón N. López-Gil
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The aim of this study is to experimentally measure the depth of field (DoF) of the human eye when it is accommodating to a stimulus of different letters size, whose distance to the subject varies
University of Murcia and University of Valencia
A commercial adaptive optics system with a deformable mirror (crx1, Imagine Eyes, France) was used. The target used consisted on high contrast black letters of different sizes on a white background displayed on a microdisplay inside the crx1. At first, we measured at 7 different accommodative states, from 0 to 6 D, the aberrations present in 7 young eyes, one per subject (29.7 ±7.7 years). In a second step, we paralyzed the accommodation of the eye (cyclopentolate) and measured the aberrations. With the adaptive optics system we compensated aberrations of the paralyzed eye, and, at the same time, we simulated the aberrations of the accommodated eye (with the same natural pupil diameter) measured in the first step. We obtained the DoF by placing the target at a vergence corresponding to the simulated aberrations and moving it towards and away from the eye with 0.2 D step. Three DoF measurements were taken using the objectionable blur as criteria. We performed this procedure for each accommodative state measured at the beginning of the experiment.
For a certain letter size, DoF values obtained in the accommodative range measured were approximately constant, showing a slight tendency to increase with stimulus demand. Mean value of DoF of all subjects was around 0.9 D for a letter size corresponding to 0.3 logMAR and increased slightly 0.2 D for the maximum accommodative demand (6D). This increase can be attributed to the decreases of the pupil diameter during accommodation, which was about 1 mm in the full range of accommodation used. Accommodating LAG increased with accommodative demand, most of it corresponding to the DoF, especially for large demands or accommodations.
For the first time it has been measured the real subjective DoF for different accommodation states. The eye presents a real LAG which depends on the letter size of the chart used as stimulus, the accommodative demand, and pupil size. Subjective DoF is usually smaller than 1.1 D. The results indicate that human eye uses DoF to accommodate less even though there is a deterioration of the retinal image quality.