Abstract
Abstract: :
Purpose: The purpose of this study was to examine motion detection thresholds and cortical VEP responses to horizontally moving patterns in normal babies and babies with infantile esotropia (infET) between 1 and 48 months of age. Methods: We developed an FPL paradigm to obtain motion detection thresholds as a function of motion signal (% moving dots) in infants. Two random–dot patterns were presented on each trial, one on the left and one on the right side of the monitor. One pattern contained only stationary dots, while the other contained a variable proportion of moving and stationary dots. Under monocular viewing, detection thresholds were obtained for each direction of motion by varying the proportion of moving dots in interleaved nasalward (N) and temporalward (T) 2–down–1–up staircases. Monocular VEP responses were obtained while subjects viewed a 6 Hz oscillating 1 cyc/deg vertical sine–wave grating. Nasal–temporal asymmetry was defined as a significant first harmonic component for each eye and a 180 deg interocular phase difference. Both measures were obtained monocularly. Participants were 82 normals and 87 infET. Of these, 31 normals and 26 infET performed the two tasks within the same day. Results: Normal infants under 2.2 months of age had symmetrical N and T motion detection thresholds. From 3.0 to 6.0 mos, N thresholds were 4X better than T thresholds. By 8 months, N and T thresholds returned to symmetry, matching that of adults. A similar pattern was observed in the motion VEP data: only 29% of normals under 2.0 mos had asymmetric VEPs, while 60% of 2.0–4.0 month olds were asymmetric, and the asymmetry diminished thereafter (0% after 7 mos). Although the two measures were similar, there was no correlation within individuals, and the peak of the VEP asymmetry preceded the motion detection asymmetry by 2 months. Like the normals, the youngest infET patients (4.5–6.5 mos) showed a nasalward superiority in both motion detection and asymmetric VEP responses, however, these asymmetries remained constant with age and were significantly greater than normals after 6.5 mos of age. Conclusions: Both motion detection and cortical motion VEP responses generated a nasal–temporal asymmetry with a similar timecourse, peaking at 3 to 5 months and declining thereafter. However, as there was no correlation within individuals, these may be independent mechanisms or FPL preference for moving patterns may mature later than VEP responses (i.e., area MT later than V1). The initial development of motion processing is normal in infantile esotropia and is disrupted over time.
Keywords: strabismus • motion–2D • infant vision