Interobserver reliability of the prism and alternate cover test in children with esotropia.
OBJECTIVE
To determine 95% limits of agreement on a measurement and on a difference between 2 measurements for the prism and alternate cover test (PACT) at distance and at near fixation.


METHODS
In a test-retest reliability study, 143 children aged 60 months or younger with esotropia were examined by 2 masked examiners on 1 or 2 occasions yielding 199 test-retest pairs for PACT at distance fixation and 239 test-retest pairs for PACT at near fixation.


RESULTS
For angles greater than 20 prism diopters (PD), the 95% limits of agreement on a measurement and on a difference between 2 measurements were +/-7.3 PD and +/-10.4 PD, respectively, for PACT at distance and +/-8.3 PD and +/-11.7 PD, respectively, for PACT at near. For angles of 10 to 20 PD, the 95% limits of agreement on a measurement and on a difference between 2 measurements were +/-4.1 PD and +/-5.8 PD, respectively, for PACT at distance and +/-3.3 PD and +/-4.7 PD, respectively, for PACT at near.


CONCLUSIONS
In childhood esotropia, differences of 12 PD or more for angles greater than 20 PD and differences of 6 PD or more for angles between 10 PD and 20 PD are likely to indicate real change. Smaller differences could be real change but could also be due to measurement error.
D002675:Child, Preschool; D004948:Esotropia / Q000175:diagnosis*; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D015588:Observer Variation; D015203:Reproducibility of Results; D014787:Vision Tests / Q000592:standards* / Q000706:statistics & numerical data; D015348:Vision, Binocular