Detection of nonorganic visual loss with a new optotype chart in simulated malingerers

We tested a new distance and pocket optotype chart for detection of nonorganic symmetrically decreased vision in simulated malingerers. The new optotype used in the charts is based on a subjective contour formed by a misalignment of two line segments. The minimum angle of resolution of this optotype is independent of its size. Subjects claiming to see only the larger optotypes are suspected of malingering.

90 normal subjects were asked to simulate symmetrically decreased vision. 60 of these subjects were tested with a distance chart and 30 with a pocket chart. The distance chart was always presented at a fixed distance of 5 m. The pocket chart was moved towards the malingerer until the largest optotype was clearly legible.

With the distance chart, 62 % (37/60) of all simulated patients claimed to recognize only the larger optotypes, 33 % (20/60) claimed not to recognize any optotype size, and 5 % (3/60) were able to read all optotype sizes. With the pocket chart, 84 % (25/30) of all simulated patients claimed to recognize only the larger optotypes, 3 % (1/30) claimed not to recognize any optotype size, and 13 % (4/30) were able to read all optotype sizes. The difference between the two distributions of behavior was statistically significant (chi-square statistic, P < 0.005).

Movement of the chart towards the subject (pocket chart) was better at detecting nonorganic visual loss than using a fixed distance (distance chart). Therefore, we suggest to use the pocket chart for the detection of nonorganic disease.