[The closed Landolt ring--a handy test for evaluating suspected simulation].

PURPOSE

We present a visual acuity test for proof of malingering and psychogenic impairment of visual acuity.

METHOD

The book contains 36 plates. On 32 plates, a Landolt-C is shown with a gap of 10 minutes of arc, thus corresponding to a visual acuity of 0.1, when applied at a distance of 1 metre. Each of the 4 alternatives of the Landolt-C occurs eight times in random order. Starting at position 21, four plates are interspersed showing a closed circle of the same size. The test is used at a distance corresponding to an acuity level of maximum 50% of the presumed factual acuity. Following a four alternative forced choice paradigm, the tested person is requested to call the direction of the Landolt-C within about 2 seconds, when the plates of the book are turned over. The responses and their latency are recorded using a digital electronic system which allows later audiovisual analysis. The response on the first closed circle and its latency is compared to the previous responses. Two subjects were tested who tried to pretend a reduction of their visual acuity.

RESULTS

Malingering was proved by the verbal response of the first subject and by the long latency of the response of the second subject (4.0 s vs. 1.2 s-2.7 s for the previous responses). The entire test, explanation included, took less than 5 minutes.

CONCLUSION

This handy test can be a useful tool in cases suspect of malingering or psychogenic impairment of visual acuity.