[Strategies of visual acuity assessment]

Visual acuity can be assessed by different strategies. The constant-stimulus-, the stair-case-, the Best-PEST-strategies, and the EN ISO 8596 are discussed. In cases of presumed psychogenic visual impairment and malingering it can be useful to modify these strategies striving for a determination of the (minimum) visual acuity based on statistical analysis rather than "clinical experience". The EN ISO 8596 defines visual acuity by a 60 % criterion, thus implying guesswork, if recognition of the optotypes is uncertain. Therefore, the forced-choice-procedure is mandatory. Objective psychophysical (preferential looking, induction or suppression of rhythmic eye movements) and electrophysiological methods (VEP) of visual acuity assessment can be useful in infants, in the mentally handicapped, and in patients with presumed psychogenical influence or malingering.