Utility of square-wave gratings to assess perioral spatial acuity

Purpose: The usefulness of square-wave gratings to assess perioral spatial resolution acuity was evaluated. Materials and Methods: A psychophysical tracking procedure was used to estimate the threshold groove width for discriminating orientation (horizontal or vertical) of square-wave gratings pressed into the skin, Ten positionally matched sites on the two sides of the face of 36 right-handed, healthy young adults were studied, Commercially available gratings provided alternating ridge-and-groove stimuli with element widths from 0.35 to 3.0 mm, Results: Thirty-three of the 36 subjects could discriminate orientation al all six sites on the vermilion (threshold width averaged 1.06 mm for grooves and for ridges), Thresholds were lower on the mid-portion of the lower vermilion than on the mid-portion of the upper vermilion (P < .05), Moreover, thresholds were lower on the right side of the vermilion than on the left side (P < .02), In contrast to the vermilion, only 25 and 30 subjects could discriminate orientation on the left and right hairy upper lip, respectively; and two or fewer subjects, at each of 12 sites on the chin and cheeks. Conclusions: Clinical use of small square-wave gratings with ridge and groove widths of 3 mm or smaller is limited to the vermilion, Moreover, baseline values are needed for individual patients to minimize false-positive diagnoses of sensory impairment, The size required of coarser gratings to test other perioral sites may preclude their use for evaluation of discrete, suspect skin areas.