The Measurement and Clinical Implications of the CA/C Ratio in Binocular Vision: A Literature Review

Abstract

Aim: This work summarises research on the convergence accommodation to convergence (CA/C) ratio, including the methods used to measure it in both laboratory and clinical settings. It explores the role of the CA/C ratio in the diagnosis and treatment of binocular and accommodative dysfunctions, considers its potential association with myopia, discusses age-related differences, examines its relationship with the accommodative convergence to accommodation (AC/A) ratio and reviews established normative values. Methods: A literature-based narrative review was carried out on the CA/C ratio and/or convergence accommodation, vergence accommodation and vergence interaction. Results: Research to date indicates that the CA/C plays an important physiological role in binocular vision, as well as in binocular and accommodative dysfunctions. It declines with age, does not appear to be related to the onset of myopia, and has a normative value (for adults) of 0.08 ± 0.02 D/Δ, 95% confidence interval (CI) of (0.07, 0.08). Conclusions: This literature review highlights the complexity of measuring the CA/C ratio, its potential value in visual assessment and its relevance to binocular and accommodative dysfunctions. Although it is not commonly measured in clinical practice, current evidence suggests that the CA/C ratio plays an important role in visual diagnosis and management. To support its clinical integration, future research should focus on developing standardised protocols for its evaluation.