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Subjective refraction of the peripheral field using contrast detection acuity.

BACKGROUND
Although peripheral resolution acuity is relatively unaffected by uncorrected refractive error, recent investigations of peripheral vision indicate that contrast detection is optically limited. It should be possible, therefore, to perform a subjective refraction in the peripheral visual field using a contrast detection task.


METHODS
For a range of trial lenses, contrast detection acuities for vertical and horizontal gratings were measured with a two-interval forced-choice paradigm. Lens powers that maximized detection acuity were taken as the subjective refraction estimates. These powers were compared with objective refractions determined with retinoscopy and autorefractometry.


RESULTS
Contrast detection acuity varied significantly with lens power at all retinal locations tested. Defocusing by one diopter from the optimum lens power reduced detection acuity by about a factor of two at 20 degrees eccentricity, and slightly less in the far periphery. Objective retinoscopy and autorefractometry agreed with subjective measurements for most conditions tested.


CONCLUSIONS
Contrast detection acuity in the peripheral visual field varies with refractive blur, demonstrating the feasibility of performing subjective refraction in the periphery for a contrast detection task. Results suggest that visual fields measured with standard perimetry, which is based on contrast detection, may be affected by uncorrected peripheral refractive errors.