Abstract
Abstract: :
Purpose: Extremely premature infants are at high risk for visual pathway deficits, since this pathway undergoes its most significant development during the prenatal and neonatal period. However, the development of visual function in the absence of serious injury has not been well defined in these infants. We used the sweep visual evoked potential (sVEP) to compare visual function in very low birth infants (24–32 weeks gestation) who do not have severe retinopathy of prematurity (ROP) or intraventricular hemorrhage (IVH) to that of healthy term infants of the same postconceptional age (PCA). Methods: Twenty–two VLBW and 22 healthy, term control infants were enrolled. Inclusion criteria included a gestational age (GA) of 24 –32 weeks and birth weight Stage II ROP or any IVH were excluded. Three different measures of visual functioning were assessed at 5 – 7 months PCA: contrast sensitivity (CS), grating acuity (GA), and vernier acuity (VA). Each measure reflects a different functional processes of the visual system . CS was measured using a phase–reversing, 2 cycles per degree (cpd) sinewave grating that was swept from 20 to 0.5% contrast over a 10–second trial. GA was measured using an 80% contrast grating that was swept from 2 to 16 cpd. VA was measured using a 2 cpd, 80% contrast grating, and its lateral offset was swept from 8 to 0.5 arcmin. The modulation frequency of the gratings was 3.76 Hz. Evoked responses were recorded from three electrodes centered on Oz. Thresholds and amplitudes for each of these measures were compared between the two groups. Results: There were no differences in mean thresholds of CS, GA, or VA between the groups. Mean thresholds for CS, GA and VA in VLBW and controls was 57.2 vs 49.5, 12.2 vs 12.9 cpd, 1.2 vs 1.0 arcmin, respectively. However, the amplitude response functions in VLBW infants for contrast sensitivity and vernier acuity were significantly higher (p<.04 and p<.02, respectively). Conclusions:Visual function thresholds for VLBW infants with no serious retinal or neurological abnormalities are comparable to that of term infants. Thus, the additional visual experience in the VLBW group does not appear to affect visual sensitivity about threshold. The higher amplitudes in this group do suggest, however, that visual experience affects responses for supratheshold stimuli. The higher amplitudes in the premature group may be indicative of accelerated maturation. These results suggest that premature infants with little of no retinal or cerebral abnormalities show impressive resistance to deficits in visual functioning.
Keywords: retinopathy of prematurity • visual development: infancy and childhood • electrophysiology: clinical