Abstract

The contrast thresholds were measured under controlled experimental conditions for a point-like source of light for different degrees of out-of-focus retinal images, in the periphery out to 12 arc degrees, under photopic conditions. As previously shown, the threshold rises with blurring of the image; but the rate of this increase becomes less as the peripheral angle becomes larger. Although the contrast threshold increased nearly linearly with peripheral angle, the rate of increase for blurred imagery was less, so that for larger peripheral angles blurredness had less influence on contrast threshold. From a theoretically derived equation, curves were fitted to the sets of data, from which the angular diameters of a minimal effective retinal area were calculated for each peripheral measurement. The results suggested that the minimal effective area of the retina was due mostly to dioptric factors rather than to retinal sensorial units.

© 1961 Optical Society of America

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Blurring of the Retinal Image and Contrast Thresholds in the Fovea*

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J. Opt. Soc. Am. 50(4) 307-315 (1960)

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