AC/A Ratio
Pronunciation: AY-see-ay ratio
Also written as: AC/A — Accommodative Convergence/Accommodation
The relationship between accommodative convergence and accommodation, measured as prism diopters of convergence per diopter of accommodation.
Full Definition
The AC/A ratio (accommodative convergence/accommodation ratio) quantifies how much convergence occurs for each diopter of accommodative stimulus. Normal values range from 3:1 to 5:1, meaning 3-5 prism diopters of convergence for each diopter of accommodation. Elevated ratios (>6:1) indicate excessive accommodative convergence and may lead to esotropia at near fixation, while low ratios (<2:1) suggest accommodative convergence insufficiency. The ratio can be measured using gradient or heterophoria methods, with implications for spectacle prescriptions and surgical planning. Understanding the AC/A ratio is crucial for managing accommodative esotropia and determining appropriate bifocal prescriptions in children.
Usage
Usage note: Express as a ratio (e.g., 5:1) and specify measurement method used; always include the slash in AC/A.
In Context
- "The patient's elevated AC/A ratio of 8:1 explained the large esotropia at near despite minimal distance deviation." — Strabismus evaluation report
- "Bifocal prescription was determined based on the AC/A ratio measurement and near-distance deviation differences." — Optical management documentation