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This term designates various devices that enable the subject to determine his own ametropia. Consequently, he may determine the best correction for his condition. These devices are not frequently used and generally are not as good as those described in the preceding chapter. In most of these devices, the subject must look with one eye in an eyepiece, which has the major inconvenience of inducing accommodation in the subject, who is not relaxed because he is trying to pay attention. This defect is lessened if the eye that is not observing, instead of remaining closed, looks at a uniform area, or even better at a distant test pattern (but then the disparity of the monocular fields may creat difficulties). We can classify subjective optometers into two categories, according to the focusing criterion that they use: sharpness or doubling.
KeywordsTest Pattern Cylindrical Lens Screen Device Corrective Lens Preceding Chapter
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