SCOTOPIC OPTOKINETIC NYSTAGMUS THRESHOLDS IN 10-WEEK-OLD INFANTS

Purpose. To compare psychophysical and reflexive optokinetic nystagmus (OKN) estimates of dark-adapted scotopic thresholds mediated by the p osterior retina in 10-week-old infants and adults. Methods. A staircas e procedure was used to determine the stimulus intensity needed to pro duce an OKN response to a moving 19 degrees X 19 degrees grating. In t he same subjects, a two-alternative, forced-choice procedure was used to obtain thresholds for detecting 10 degrees diameter, 50 ms duration stimuli. Results. Both OKN and psychophysical thresholds of infants a re 0.9 log unit higher than those of adults. Conclusion. The infant-ad ult difference in thresholds mediated by retina at the posterior pole is greater than the infant-adult difference in thresholds for full-fie ld stimuli. It is possible that delayed maturation of the posterior re tina is the primary determinant of infants' high OKN and psychophysica l thresholds.