Eccentricity Perception in the Periphery of Normal Observers and Those with Retinitis Pigmentosa

Abstract

The perception of the eccentricity of a suprathreshold light flash (III/4e) presented in a Goldmann perimeter was measured in four ophthalmologically normal observers and three young observers with retinitis pigmentosa (RP). The task was to indicate the perceived distance from central fixation of each light flash by making a mark on a 180-mm line drawn on a sheet of paper. In the center of the line was a hash mark. Observers were instructed that the hash mark should correspond to fixation and the ends of the line to the limits of the visual field. The vertical, horizontal, and both 45° oblique meridians were tested. The results showed that: 1. The extent of the field along the tested meridian determined perceived eccentricity, i.e., eccentricity of 45° in the temporal field of normals was perceived as equally eccentric as 30° in the superior field. 2. The central 20° were taken to represent more of the perceptual field than any other 20°. 3. Along a meridian, the eccentricity which extends from fixation to 16% of the way to the field limit along the meridian is perceived as extending to 25% of the field by normal observers. 4. On the other hand, observers with RP reported that along a meridian the eccentricity extending from fixation to 8% of the field limit is perceived as extending to 25% of the field. Kinetic primary with the II/4 target showed no evidence of field constriction in observers with RP. However, losses in sensitivity are evident starting at about 10°. Full field single flash electroretinograms were unrecordable in the observers with RP. The data were interpreted to reveal a perceptual magnification of the central field in the relatively early stages of RP.