Vanishing optotypes. New type of acuity test letters.

Acuity test letters generated on a television monitor were studied with regard to detection and resolution thresholds, both for the native configurations and after high-pass spatial frequency filtering. Comparisons were made with printed acuity charts of different contrast. Filtering diminished the interval between detection and resolution thresholds. Under some circumstances, a small (1 dB, about 26%) increment in size could make a previously invisible optotype clearly visible, or vice versa. The term vanishing optotype is suggested for acuity targets with this peculiar property. Vanishing optotypes do not seem useful for routine clinical acuity testing, but they may be advantageous, for example, in preferential looking-acuity tests for infants and visual field examinations. Like the present tests, such novel applications can be generated relatively easily on personal computers.