The standard approach for determining refractive error is monocular subjective refraction. In this technique the optometrist or ophthalmologist uses a phoropter to determine the endpoint at which the patient achieves best visual acuity (VA). The eye being tested is exposed to the VA chart, while the other eye is occluded. However, we view the world with two eyes (i.e., binocularly), and therefore a refraction technique conducted under binocular viewing conditions conceivably may yield more accurate results. Whereas several binocular refractive techniques exist including the Turville Infinity Balance and Vectographic Slide, they are used infrequently in standard clinical practice, and while included in optometric curriculum, are not emphasized and therefore rarely utilized by optometric students and recent optometric graduates. One such binocular technique is the Humphriss method, in which both eyes view the VA chart during refraction, but one eye (the eye not being actively tested) is defocused by a moderate degree. This creates a situation in which viewing is binocular such that focusing and eye alignment are determined by binocular perception. The technique is very quick, accurate and generally well-tolerated by the patient The purpose of this study is to conduct a systematic comparison of the binocular Humphriss technique to standard monocular refraction. The results will help determine the efficacy of the Humphriss technique, as well as providing clinical guidelines for application in optometric and ophthalmologic settings.
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