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positive relative accommodation

Positive relative accommodation (PRA) is the maximum amount of accommodation a patient can stimulate while keeping clear, single binocular vision.1 The examiner adds minus lenses binocularly in 0.25 D steps until the patient reports the first sustained blur, and the total minus added is the PRA.2

Each step of minus forces the patient to accommodate, and the extra accommodation brings extra accommodative convergence through the AC/A ratio. The target stays at 40 cm, so the patient must use negative fusional vergence to stay single. The endpoint is therefore either an inability to stimulate more accommodation or exhausted negative fusional vergence. Occluding one eye at the endpoint separates the two, because clearing of the print points to the vergence limit.3

The expected PRA in a nonpresbyope is -2.37 D, plus or minus 1.00 D.2 A low PRA can mean accommodative insufficiency or esophoria with low negative fusional vergence, and accommodative insufficiency fits only if other tests show adequate vergence.3

More detail

In the presbyope, the PRA and its partner, the negative relative accommodation, vary widely. When the near add is right, the two findings should have the same absolute value, and the sum of the add and the negative relative accommodation should not exceed +2.50 D.2

Sources (8)
  1. AOA Clinical Practice Guideline, Care of the Patient with Accommodative and Vergence Dysfunction, Glossary
  2. Carlson and Kurtz, Clinical Procedures for Ocular Examination, ch. 4
  3. Scheiman and Wick, Clinical Management of Binocular Vision, ch. 2
  4. Carlson, N.B. and Kurtz, D. 2004. Clinical procedures for ocular examination. 3rd ed. New York: McGraw-Hill.
  5. Grosvenor, T. 2007. Primary care optometry. 5th ed. St. Louis: Butterworth-Heinemann Elsevier.
  6. Rutstein, R. and Daum, K. 1997. Anomalies of Binocular Vision: Diagnosis & Management. St. Louis: Mosby.
  7. Scheiman, M. and Wick, B. 2014. Clinical management of binocular vision: heterophoric, accommodative, and eye movement disorders. 4th ed. Philadelphia: Lippincott Williams & Wilkins.
  8. Siderov, J. and Tiu, A.L. 1999. Variability of measurements of vergence facility in subjects with myopia. Optometry and Vision Science, 76(6), pp.357-366.

Reviewed October 2026

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