Quantifying variability in the measurement of control in intermittent exotropia.

PURPOSE: To evaluate the performance of a series of summary measures of control and to assess reliability in quantifying exodeviation control in intermittent exotropia.
METHODS: A large, simulated dataset of control scores for 10,000 hypothetical patients with intermittent exotropia was created using Monte Carlo simulations. These data were based on children with intermittent exotropia in whom control was assessed twice during one clinical examination, using the office control score (0-5). Each simulated patient had a baseline and 11 subsequent control scores. The repeatability of a series of summary measures of control (the mean of 2 vs the mean of 3 up to the mean of 6), was calculated using 95% limits of agreement (LOA).
RESULTS: A total of 322 examinations in 152 patients were used to provide representative distributions of control scores. From the resultant Monte Carlo simulations, the 95% LOAs were 2.60 for 1 distance control score measure, 1.76 for the average of 3, and 1.28 for the average of 6. Therefore using the average of 3 scores, a change of <1.76 would be consistent with short-term variability, whereas a change of >1.76 would suggest a real change in control.
CONCLUSIONS: The large dataset of simulated control scores allowed us to assess the variability of specific summary measures of control. We recommend the average of 3 scores (a triple control score) as a new standard for assessing control, providing improved reliability over a single measure, while remaining implementable in clinical practice.