Interobserver reliability of the prism and alternate cover test in children with esotropia
(Fiabilité inter observateurs de l'examen sous écran alterné prismatique ches les enfants strabiques)

Pediatric Eye Disease Investigator Group

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.

CONCLUSION: 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.

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