. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, one above the other on one line, there is not supposed to beany insufficiency. If, however, there are two lines andtwo dots, and the upper dot is on the right, there is in-sufficiency of the externi (esophoria) for near. The amountof the insufficiency is represented by the strength of j^ base outward, before the left eye which will bringthe two dots exactly, on one line. If the upper dot is to 182 REFRACTION AND HOW TO REFRACT. the left, then there is insuffi
. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, one above the other on one line, there is not supposed to beany insufficiency. If, however, there are two lines andtwo dots, and the upper dot is on the right, there is in-sufficiency of the externi (esophoria) for near. The amountof the insufficiency is represented by the strength of j^ base outward, before the left eye which will bringthe two dots exactly, on one line. If the upper dot is to 182 REFRACTION AND HOW TO REFRACT. the left, then there is insufficiency of the interni (exophoria)for near, and the amount of the insufficiency is representedby the strength of prism placed base inward over the lefteye which will bring the two dots, one above the other, onone line. These tests for insufficiencies should always be made be-fore estimating the refraction, and also after the correctinglenses are carefully placed, with their optic centers, beforethe eyes. To avoid confusion in making these tests, where a pointof light is used as the fixing object, it is customary to place.
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