Comparison between grating acuity measured by visual tracking and preferential looking in infants.

BACKGROUND The aim of this study was to compare the visual acuity measured by visual tracking and by preferential looking. METHODS We examined 51 healthy full-term infants between three and 93 days of age. Visual acuity was tested with two different methods. One method was visual tracking (smooth and saccadic pursuit), recorded with an infrared photo-oculographic technique. For stimulation of visual tracking a square of 9.4 degrees of visual angle with vertical gratings (0.1, 0.2, 0.4, 0.8 and 1.6 cycles per degree) moved at a constant velocity of 7.5 degrees/sec. for 38 sec. on a surface of equal luminance. The other method was preferential looking, determined by a second examiner, where we used plates with vertical gratings (0.1, 0.2, 0.4, 0.8, 1.6, 3.2 and 6.4 cycles per degree). RESULTS The comparison of the two methods shows a significant correlation (p < 0.05). Visual acuity determined by visual tracking is lower than the acuity determined by preferential looking in the first 14 weeks of age. CONCLUSION Our study shows that visual tracking is a valid method for visual acuity testing in infants. The need of sustained attention is a possible reason for the lower values in comparison with the acuity determined by preferential looking.