Measuring accommodative facility in clinical practice

Given the longstanding view of near work as an environmental risk factor for myopia development and progression,1 many studies have explored the relationship between accommodation and myopia. 

Research suggests that esophoria and increased accommodative lag are associated with myopia compared to emmetropia.2,3 Myopic children and young adults show reduced response to lens-induced blur, reduced accommodative facility, greater variability in accommodative behaviour, and greater accommodative convergence (higher AC/A ratios) relative to emmetropes.4-7 Higher accommodative lag may be also seen in individuals who undergo myopic shifts, regardless of whether they were originally myopic or non-myopic.6

As myopia development and progression is multifactorial, assessing accommodation and binocular vision contributes an important layer to clinical decision making.

Accommodative facility is a clinical test that evaluates the eye’s ability to alter accommodation rapidly and accurately, by using alternating negative and positive lenses to induce and relax accommodation. 

It can be measured either monocularly (monocular accommodative facility, MAF) or binocularly (binocular accommodative facility, BAF). 

Whereas MAF provides a direct evaluation of the accommodative response, BAF reflects the combined response of the accommodation and vergence systems.8

Measuring accommodative facility is relevant for diagnosis of accommodative infacility, also known as inertia of accommodation or tonic accommodation. Accommodative infacility is characterised by sluggish accommodative responses between distance and near, often leading to intermittent blurred vision and/or asthenopia, in relation to prolonged near work.9

Moreover, testing the facility of accommodation is useful for predicting visual discomfort as well as academic success in school children.10,11 Accommodative facility can indicate how well a patient can cope with accommodative lag, and how much stamina they have to maintain near point focus. For example, low facility of accommodation is used a diagnostic sign for accommodative insufficiency.12

A key advantage for myopia management is that testing can be performed on children around the typical age of myopia onset (i.e. 5–6 years), as the test is quick, non-invasive, easy for children to understand, and reproducible. With age-appropriate targets and instructions, both monocular and binocular accommodative facility have been successfully measured in children aged 6–12 years.13,14

Accommodative facility testing can be performed qualitatively by observing the patient’s response times as well as their behaviour while interacting with the positive and negative lenses.

1. Provide the patient with a near chart containing N6 or smaller letters, positioned at their habitual working distance of 33 to 40 cm. Alternative accommodative targets may also be used, such as the top of an occluder paddle with descending letter sizes or the back of a Howell phoria card.
2. Prepare ±1.50 and ±2.00 flippers, combining the minus sides to create a -3.50 D demand. If lens flippers are unavailable, loose trial lenses may be used instead
3. With full distance correction in place, ask the patient to view the target through the -3.50 D lenses. The patient should be able to clear the target to a level consistent with their expected positive relative accommodation (PRA) or B- result. This provides a quick qualitative indication of accommodative amplitude response.
4. Next, switch to the plus lenses of the ±2.00 flippers, creating a +2.00 D demand. The patient should again be able to clear the target to a level consistent with their expected negative relative accommodation (NRA) or B+ result.
5. Finally, alternate several times between +2.00 and -2.00 lenses, observing the speed and consistency of clearing. Note whether fatigue occurs on either side or whether rapid clearing is maintained throughout the cycles.

Qualitative observations can be recorded like the example below:

1. "Acc fac normal" - if both -3.50, +2.00 and -2.00 are cleared swiftly and consistently
2. "Acc fac normal on plus, slow on -3.50, fatigues to fail on -2"
3. "Acc fac normal on plus, failed -3.50, cleared -2 on cycles"

If patient #2 or #3 has an accommodative lag over +1.00, accommodative facility testing gives useful insight into how much functional reserve they have to cope with that lag. Patient #2 is likely to struggle more than patient 3, as they demonstrate an initial ability to stimulate accommodation that could not be sustained, whereas patient #3 showed a consistently reduced but more stable accommodative response, clearing -2.00.

The most common method of accommodative facility testing is the quantitative method, where the clinician counts the number of successful cycles that the patient is able to clear within one minute.

A hand-held ± 2.00 D lens flipper or a phoropter can be used.15 Viewing through one side of the lens flipper, the patient is instructed to hold a near chart at 40 cm and clear one row of reduced Snellen print – i.e. fixate on the print until it becomes clear and single. As soon as the print is readable, the lenses are flipped to the opposite site and the patient is instructed to clear the print again. 

A pair of positive and negative flips is considered as one cycle, and the number of cycles completed in one minute (cpm) is recorded by the practitioner.

1. Accommodative facility indicates the ability of the visual system to adjust accommodation quickly and accurately.
2. Testing accommodative facility under monocular or binocular viewing conditions helps predict visual comfort and functional performance, particularly in relation to sustained near work.
3. While facility of accommodation is traditionally measured by counting cycles per minute, observing the patient’s subjective response to lenses can provide additional insights into their accommodative system.

Discover our Binocular Vision Fundamentals online course – designed to build your confidence and clinical precision in assessing and managing BV. 

You’ll learn our practical two-system approach to accommodation and vergence, step through key diagnostic tests, and refine your prescribing and management decisions. The course also explores how to communicate BV findings with patients and why BV is essential in myopia management – always with a sharp focus on clinical application.

Enjoy video demonstrations, real-world case examples, and downloadable chairside infographics you can use immediately in practice.