The 20-prism-dioptre base-out test: an indicator of peripheral binocularity

Area of Science:

• Ophthalmology
• Pediatric Vision
• Binocular Vision

Background:

• Assessing binocular vision in very young children is challenging due to limitations in formal sensory testing.
• Peripheral fusion is a key component of binocular single vision, important for visual development.
• Early detection of visual anomalies in children is critical for timely intervention.

Purpose of the Study:

• To evaluate the diagnostic accuracy of the 20-prism-dioptre (PD) base-out (BO) test for detecting peripheral fusion in pre-verbal children.
• To determine the utility of the 20-PD BO test as a screening tool for binocular vision in pediatric patients.

Main Methods:

• A case series design was employed at a pediatric ophthalmology service.
• The study included 80 orthophoric children and 41 children with surgically corrected infantile esotropia, with a mean age of 19 and 21 months, respectively.
• The 20-PD BO test and the red-green Worth four-dot test were administered at near distance.

Main Results:

• The 20-PD BO test demonstrated a 100% positive predictive value in orthophoric children for detecting peripheral fusion.
• In children with surgically corrected infantile esotropia, the positive predictive value was 93% (95% CI 82% to 100%).
• The negative predictive value was 21% (95% CI 0% to 43%).

Conclusions:

• The 20-PD BO test is a valuable tool for identifying peripheral fusion in young children unable to complete standard sensory evaluations.
• A positive response on the 20-PD BO test is a reliable indicator of peripheral binocular single vision in this age group.
• Despite a low negative predictive value, the test aids in the assessment of binocular function in infants and toddlers.