BISECTION JUDGMENTS IN PATIENTS WITH RETINITIS-PIGMENTOSA

1. The effects of retinitis pigmentosa (RP) on spatial position judgments were investigated in a bisection task. 2. Bisection accuracy and precision were measured at three eccentricities (1.25, 2.5 and 5.0 deg) along the superior and inferior meridians in patients with RP and compared to the data of normal subjects. 3. The results showed that some patients with RP exhibit substantial spatial position distortions; biases ranging from 2-9 SD above the mean of the normal subjects were reported for some subjects. Other patients with RP judge the relative position with the same accuracy as normal subjects. 4. The results also showed that some patients with RP had low spatial-position precision. However, many patients with RP showed the same bisection precision as normal subjects. Furthermore, some of the patients who had normal or nearly normal precision demonstrated large biases. 5. The extent of pathology (years past age of visual field loss onset) could not discriminate between the RP subjects who demonstrated poor spatial position accuracy and/or precision and those who did not.