Reproducibility of nearwork-induced transient myopia measurements using the WAM-5500 autorefractor in its dynamic mode.

Purpose: To evaluate the reproducibility of nearwork-induced transient myopia (NITM) measurements obtained objectively using an open-field autorefractor (WAM-5500) in its dynamic mode.

Methods: NITM was assessed in 22, visually-normal, teen-aged and young-adult subjects using an infrared autorefractor (WAM-5500) in the dynamic mode. Measurements were obtained from the right eye in two test sessions separated by either 30 minutes or 2 days. Initial NITM and its decay were assessed monocularly by the same experimenter immediately after binocularly viewing and performing a detailed near task (5D) for 5 minutes incorporating a cognitive demand, with habitual distance refractive correction in place. Data were averaged over 10-second bins for 3 minutes (180 seconds; 18 bins) for the decay analysis. The NITM post- minus pre-task difference and its limits of agreement (LOA), as well as intraclass correlation coefficient (ICC), were calculated to evaluate reproducibility over the two test sessions for the initial NITM magnitude and its decay.

Results: The group mean (±SE) initial NITM and its decay duration were 0.33 ± 0.09 D and 0.28 ± 0.08 D, and 118.6 ± 14.3 seconds and 132.3 ± 12.2 seconds respectively, for each test session, which were not significantly different (p > 0.05). The difference (range), LOA, and ICC (95% confidence interval [CI]) were 0.06D (-0.15, 0.64), -0.29 to 0.40D, and 0.90D (0.77, 0.96) for the initial NITM; they were -13.6 (-150.0, 140.0) seconds, -174.5 to 147.3 seconds, and 0.14 (0.00, 0.52) for decay duration, respectively, for each test session. The ICC range for the first 50 secs of the NITM response/decay was 0.90 to 0.96.

Conclusions: The initial NITM was highly repeatable. The initial decay phase was moderately repeatable, with the later decay phase being more variable, yet still yielding acceptable reproducibility in many cases. Both of these key parameters, namely initial NITM and its early decay, can be assessed reliably and with good reproducibility. This is important in future longitudinal studies of NITM, and its possible relation to refractive development.