Accommodation Testing: Amplitude, MEM and Nott Retinoscopy, Facility, NRA and PRA
Last updated: November 2026
RPC Rounds for Optometrists · B.Optom study guide
Accommodation testing takes about five minutes and answers three questions: how much can the eye focus (amplitude), how accurately does it focus (lag or lead), and how quickly and flexibly does it change focus (facility and relative accommodation).
Amplitude of accommodation
| Method | How | Notes |
|---|---|---|
| Push-up (Donders) | With distance correction, move an N5/N6 target towards the eye until it first stays blurred; amplitude = 1 ÷ distance (m) | Overestimates slightly (depth of focus and target magnification); do monocularly then binocularly |
| Push-down | Start close and move away until it clears | Averaging push-up and push-down reduces error |
| Minus-lens method | At 40 cm (2.50 D demand), add minus until sustained blur; amplitude = total minus + 2.50 D | Underestimates slightly (target minification) |
| RAF rule | Ruler with a sliding target gives near point directly in dioptres | Also measures near point of convergence |
Hofstetter's formulas: minimum = 15 − 0.25 × age; average = 18.5 − 0.3 × age; maximum = 25 − 0.4 × age. An amplitude more than 2 D below the minimum for age is abnormal. A difference of more than 1 D between eyes is significant.
Accuracy: dynamic retinoscopy
| Test | How | Normal |
|---|---|---|
| MEM (monocular estimate method) | Patient reads a card on the retinoscope at their working distance with distance correction; briefly place a lens before one eye to neutralise the reflex | Lag of +0.25 to +0.75 D; over +0.75 D suggests insufficiency or uncorrected hyperopia; minus (lead) suggests excess |
| Nott retinoscopy | Card fixed at 40 cm; the examiner moves backwards until neutral | Neutral point just behind the card (lag about 0.25–0.75 D) |
| Binocular cross-cylinder | Cross-cylinder over a grid target at near in dim light | Plus added to equalise lines estimates the lag |
Flexibility: facility and relative accommodation
| Test | How | Normal (approximate) |
|---|---|---|
| Accommodative facility | ±2.00 D flippers at 40 cm with a small target; count cycles per minute (one cycle = clear through plus and minus) | About 11 cpm monocular and 8 cpm binocular in young adults; lower in young children |
| NRA (negative relative accommodation) | At 40 cm binocularly, add plus in 0.25 D steps until first sustained blur | About +2.00 to +2.50 D |
| PRA (positive relative accommodation) | At 40 cm binocularly, add minus until first sustained blur | About −2.25 to −2.50 D or more in pre-presbyopes |
For prescribing a near add in early presbyopia, the add that centres the NRA/PRA balance (add = (NRA + PRA) ÷ 2 added to the trial add) gives a comfortable range.
Putting it together
| Pattern | Suggests |
|---|---|
| Low amplitude, high lag, fails minus, low PRA | Accommodative insufficiency (or early presbyopia) |
| Normal amplitude, fails both plus and minus | Accommodative infacility |
| Low NRA, low lag or lead, fails plus | Accommodative excess |
| Low amplitude falling with repeat testing | Ill-sustained accommodation |
Always test with the full distance correction in place, good light and a target one line above the best near acuity. See accommodative anomalies for management.
Practical pearls
- Measure amplitude monocularly and binocularly: binocular amplitude is usually a little higher because convergence helps.
- For MEM, flash the lens in front of the eye for under a second so it does not change the accommodation you are measuring.
- Facility norms are lower in young children: compare with age norms, not adult values.
Where students slip
- Testing amplitude without the distance correction in a hyperope.
- Using a large target, which overestimates the push-up amplitude.
- Counting a facility cycle as only one lens flip.
Test yourself: flip cards
Quick quiz
Related: Accommodative Anomalies and Vision Therapy: Insufficiency, Excess, Infacility and Spasm, Refraction Calculators: Near Add, AC/A Ratio, Retinoscopy and Prism, Subjective Refraction Step by Step: Fogging, Best Sphere, Cross-Cylinder, Binocular Balance and Near Add, Convergence Insufficiency and Convergence Excess: Diagnosis, Treatment and Exercises, Orthoptic Tests Made Easy: Cover Test, Hess Chart, Synoptophore, Worth 4-Dot and Stereopsis. Back to the optometry curriculum.
Key sources
- Scheiman M, Wick B. Clinical Management of Binocular Vision. 5th ed. Wolters Kluwer; 2019
- Elliott DB. Clinical Procedures in Primary Eye Care. 5th ed. Elsevier; 2020
- Hofstetter HW. Useful age-amplitude formula. Optom World. 1950;38:42-45
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