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The 20-prism-dioptre base-out test: an indicator of peripheral binocularity
1Ivey Institute of Ophthalmology, Children's Hospital of Western Ontario, London.
Objective:
To assess the ability of the 20-prism-dioptre base-out test to detect the presence of peripheral fusion in children too young to undergo formal sensory testing.
Design:
Case series.
Setting:
Pediatric ophthalmology service at the Children's Hospital of Western Ontario, London.
Patients:
Eighty orthophoric patients (mean age at presentation 19 months [range 4 to 50 months]) with a family history of strabismus or with a diagnosis of pseudostrabismus, blocked tear duct or chalazion, followed for an average of 36 (range 6 to 129) months, and 41 patients with surgically corrected infantile esotropia (mean age at testing with the 20-PD base-out test 21 months [range 9 to 50 months]), followed for an average of 53 (range 14 to 117) months.
Interventions:
Twenty-PD base-out test and red-green Worth four-dot test at near (0.3 m).
Outcome Measure:
Presence of peripheral fusion.
Results:
The 20-PD base-out test had a positive predictive value of 100% in detecting peripheral fusion in the orthophoric patients and 93% (95% confidence interval [CI] 82% to 100%) in the patients with surgically corrected infantile esotropia.
Conclusions:
Although the 20-PD base-out test had a negative predictive value of 21% (95% CI 0% to 43%), a positive response remains a useful indicator of peripheral binocular single vision in children too young to undergo more formal sensory testing.