fusional vergence amplitude
The maximum amount of convergence or divergence a patient can exert to maintain single binocular vision when tested with prisms.
Full Definition
Fusional vergence amplitude measures the eye's ability to overcome prism-induced disparity while maintaining fusion. It is tested by gradually increasing prism power until diplopia occurs or fusion breaks down. This measurement is critical in pediatric ophthalmology for assessing binocular function and determining surgical timing for strabismus. Normal values vary by age, with children typically showing greater fusional reserves than adults. Reduced fusional amplitudes may indicate underlying binocular dysfunction or predict post-surgical outcomes.
Usage
Usage note: Always specify the direction (base-in, base-out, base-up, base-down) when documenting measurements.
In Context
- "The patient's fusional vergence amplitude of 8 prism diopters base-out suggested adequate reserves for binocular fusion." — Clinical examination report
- "Post-operative fusional vergence amplitude testing showed improved binocular stability following horizontal muscle surgery." — Surgical follow-up note