Evaluation of methods for assessing visual function of infants

Purpose: Commonly used behavioral and electrical testing methods for estima tion of visual acuity and visual function in infants yield different estima tes and may not accurately predict visual acuity and visual function in lat er life. Moreover, neither test-retest variability nor side-by-side compari sons of the various methods have been thoroughly evaluated in the same infa nt population. The purpose of this study was to provide such an evaluation. Method: The test-retest variability of visual acuity and visual function w as evaluated for the Teller Acuity Card (TAC) procedure, sweep visual evoke d potential (VEP), as well as latency and amplitude measured by transient p attern VEP. Groups of approximately 20 infants contributed test-retest data . Visual function estimated by the various methods in a larger group of inf ants (n = 118) was compared. Correlations between methods and the validity of the various methods to detect maturational changes between 4 and 8 month s of age were also assessed. Administration of these tests was according to standard and usual procedures. Results: The average percent difference bet ween test and retest estimates of acuity as well as the SD was lowest for t ransient VEP latency (3%, 7% SD). The other methods were markedly more vari able: sweep VEP (2%, 22% SD), TAC procedure (8%, 20% SD), and transient VEP amplitude (7.5%, 39% SD). Average coefficients of variation showed a simil ar trend: transient VEP latency, 8%; sweep VEP, 15%; TACs, 30%; and transie nt amplitude, 53%. Correlations among estimates by the methods were poor, b ut expected changes in visual maturation from 4 to 8 months of age were det ected with all methods. Conclusions: All methods evaluated provide valid an d reliable test-retest data for a group, but are less valid for estimating visual acuity and visual function of an individual subject, The poor correl ations between any 2 of the testing methods suggest that each test assesses a different aspect of vision. Nonetheless, expected maturational changes b etween 4 and 8 months of age were readily detectable by all methods evaluat ed.