accommodative convergence
Accommodative convergence is the convergence that occurs reflexly in response to a change in accommodation.1 A given amount of accommodation elicits a set amount of convergence, and this linkage shapes binocular vision at near fixation.2
Convergence, accommodation and pupillary miosis come into play together during near vision and are called the near triad. The oculomotor nerve serves all three, so a disturbance of one may be accompanied by the others.3 The AC/A ratio expresses a person's convergence response, in prism diopters, to each diopter of accommodation. In theory accommodative convergence would meet the whole convergence requirement at near, but in most people the ratio falls short of it.2
The normal range of the AC/A ratio is 3 to 5 prism diopters per diopter. Values above 5 denote excessive accommodative convergence, and values under 3 denote an insufficiency.2 Reduced accommodative effort reduces accommodative convergence, so uncorrected myopes, presbyopes wearing reading glasses and absolute hyperopes can develop convergence insufficiency.4
More detail
The heterophoria method measures the deviation at distance with full correction and again at 33 cm, and attributes the change to accommodative convergence. The gradient method holds the fixation distance constant and changes the stimulus to accommodation with minus and plus lenses.2,5 Clinicians often estimate the ratio by simply comparing the distance and near deviations, but the labels normal and excessive should be reserved for a ratio that has actually been calculated.2 A ratio of 4:1 is also cited as normal.5
Sources (11)
- Pickwell's Binocular Vision Anomalies, Glossary
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 5
- Pickwell's Binocular Vision Anomalies, ch. 2
- Pickwell's Binocular Vision Anomalies, ch. 8
- Care of the Patient with Accommodative and Vergence Dysfunction (AOA guideline), Supplemental Tests
- Caloroso, E.E. and Rouse, M.W. (1993) Clinical management of strabismus. Boston: Butterworth-Heinemann.
- Kersten, D. and Legge, G.E. (1983) 'Convergence accommodation', Journal of the Optical Society of America, 73(3), pp. 332–338.
- Noorden, G.K. von and Campos, E.C. (2002) Binocular Vision and Ocular Motility: Theory and Management of Strabismus. 6th edn. St. Louis: Mosby.
- Rowe, F.J. (2012) Clinical Orthoptics. 3rd edn. Chichester, West Sussex: Wiley-Blackwell.
- Tamhankar, M.A. (2023) A-Pattern Esotropia and Exotropia: Background, Pathophysiology, Epidemiology, Medscape. Available at: https://emedicine.medscape.com/article/1199362-overview (Accessed: 5 May 2024). secondary
- Viccars, V. (2022) Physiology, Accommodation - StatPearls - NCBI Bookshelf. Available at: https://www.ncbi.nlm.nih.gov/books/NBK542189/ (Accessed: 5 May 2024). secondary
Reviewed October 2026