Vernier acuity cards: a practical method for measuring vernier acuity in infants.

Abstract

The feasibility of a practical preferential looking technique, similar to Teller acuity cards, was investigated for the assessment of vernier acuity in preverbal infants. Forty-two infants ages 1 to 13 months were tested with cards having vernier offsets of 2 to 64 minutes of arc and spatial frequencies of 0.25 to 2.0 cycles per degree. All infants showed a robust preferential looking response to the largest vernier offsets. Vernier thresholds decreased with age from 64 minutes of arc at 1 month to 4 minutes of arc at 13 months. Smaller vernier offsets were more readily detectable when embedded in higher spatial frequency gratings. Vernier acuity can be assessed in preverbal infants using a preferential looking technique similar to that employed with the Teller acuity cards. Vernier acuity is known to be more sensitive to amblyopia than grating acuity; therefore, this technique may prove useful in the assessment of amblyopia.