Similarities and differences between behavioral and electrophysiological visual acuity thresholds in healthy infants during the second half of the first year of life.

PURPOSE

Behavioral and electrophysiological methods for visual acuity estimation typically correlate well in children and adult populations, but this relationship remains unclear in infants, particularly during the second half of the first year of life. It has been suggested that the agreement between both methods mostly relies on age and/or subjective acuity factors. The present study aimed at comparing acuity thresholds obtained with both approaches in a sample of healthy infants in a relatively narrow age range, that is 6-10 months old.

METHODS

Acuity thresholds were assessed in 61 healthy infants aged between 6 and 10 months using the Teller acuity cards (TAC) and sweep visual evoked potentials (sVEP). The TAC stimuli (stationary vertical gratings displayed on laminated cards) ranged from 0.31 to 38 cycles per degree (cpd). The TAC acuity threshold was estimated according to the highest spatial frequency scored by the experimenter as seen by the infant. The sVEP stimuli (high-contrast vertical gratings counter-phased at 12 reversals/s) ranged from 13.5 to 1 cpd. sVEP were recorded at Oz and acuity threshold was estimated using regression linear fitting.

RESULTS

Considering the entire sample, sVEP acuity thresholds (8.97 ± 2.52 cpd) were significantly better than TAC scores (5.58 ± 2.95 cpd), although the difference was within 1 octave for 64% of the infants. Neither Pearson nor intra-class correlations between the two methods were significant (0.18 and 0.03, respectively). While age at assessment was not related to any dependent variable (TAC, sVEP, sVEP-TAC difference score), subjective (behavioral) acuity was found to underlie the difference between the two methods. The difference between sVEP and TAC scores decreased as a function of subjective acuity, and at the highest subjective acuity level (>10 cpd), TAC acuity slightly exceeded sVEP acuity.

CONCLUSIONS

The superiority of sVEP acuity often reported in the literature was evident in our infant sample when subjective acuity (TAC) was low or moderate, but not when it was high (>10 cpd). The relationship between the two estimation methods was not dependent on age, but on subjective acuity.