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B.-C. Jiang, H. Lin; A Comparison Between Objective Depth-Of-Focus and Subjective Depth-Of-Focus. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1788.
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To compare the depth-of-focus (DOF) measured with objective and subjective methods.
Twelve emmetropes participated in this study. High contrast square-wave grating(s) with spatial frequency 17 c/d were used as the target in both experiments. In the DOF objective measurement, the subject’s right eye looked at the target through a Badal stimulator. The vergence of the target (i.e. accommodative stimulus, AS) changed from 0.9 D to 2.1 D with 0.1 D step. The subject’s accommodative responses (ARs) were recorded by a Canon R-1 optometer. The ARs at each AS level were compared with the ARs to the AS of 1.5 D. The objective DOF was determined as the difference between the AS, at which level the ARs were significantly different from the ARs at 1.5 D AS level, and the 1.5 D. The subjective DOF was measured using a two-channel Badal system. The subject’s right eye looked through the system to view two identical targets. One target was positioned at 1.5 D and the other was moveable. Each target occupied one- half of the visual field. The subject was instructed to fixate at the fixed target and move the moveable target until a just noticed blur was detected. The difference between the positions of the two targets in diopters was defined as the subjective DOF.
The mean of the objective DOF determined in this study was ± 0.0913 ± 0.032 (S.D.) diopters. The mean of the subjective DOF was ± 0.525 ± 0.295 diopters. A paired t-test showed that the difference is significant ( t  = 5.31, p < 0.0001).
The results of this study suggest that the sensory-motor threshold to blurring of the retinal image is more sensitive when compared with the defocus threshold of the visual perceptual system in the same subject.
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