Dark-adapted thresholds at 10- and 30-deg eccentricities in 10-week-old infants

We tested the hypothesis that the dark-adapted sensitivity of the near central retina is lower than that of peripheral retina in 10-week-old infants. A spatial two alternative forced-choice psychophysical method was used to estimate the threshold for 2-deg spots presented 10 deg and 30 deg from the center of a screen. Each 10-week-old infant (n = 11) and adult (n = 5) subject was tested at both eccentricities. Every infant's threshold at 10 deg is higher than that at 30 deg. The median difference between the infants' thresholds at 10 deg and 30 deg is about 0.5 log unit. Whereas the scotopic thresholds of adults at 10 deg and 30 deg are virtually identical, the thresholds of infants' near central retina are higher than those in more peripheral retina. Delayed maturation of the near central rod outer segments with consequent lower quantum catch may be the primary determinant of this infantile sensitivity pattern.