Accommodation

What it measures

The screen task measures how small a printed number the patient can still read correctly at their working distance, and how reliably they read it. That is a near resolution task under a sustained accommodative demand.

It sits alongside the two properties a full accommodative assessment covers, both of which are measured by hand rather than on screen. Amplitude is how much accommodation the eye can produce, taken from the near point and expressed in dioptres. Facility is how quickly accommodation switches between two demands, counted in cycles per minute with flipper lenses.

The two dissociate: a patient can have an amplitude appropriate for their age and still change focus slowly, the pattern in accommodative infacility. Amplitude declines steadily with age, so a value is read against age, not against a single cut-off.

How it is administered

The patient wears the near correction they would normally use at the screen distance, and sits far enough back to read comfortably without leaning in. Keep the working distance steady, because the task has no distance sensor and a patient who creeps forward makes the smallest size easier.

A grid of numbered tiles is shown, each tile printed at a smaller size than the last. The patient picks a tile, reads the number aloud, and types it back. The round advances whether the answer is right or wrong, so the run covers the full ladder rather than stopping at first failure.

Set the number of rounds before starting. Even, glare-free lighting matters as much here as on a printed near card. Watch for a head that creeps forward, for squeezing, and for answers guessed rather than read.

Reading the result

VisReed runs its own screen task: numbers printed at decreasing sizes, one read back per round. It records the proportion read correctly and the smallest size read. The amplitude in dioptres and the facility count are measured with the near rule and the flipper lenses, and the clinician writes them in the notes.

Read amplitude against published age norms: a value that is unremarkable at 45 is low at 12. A difference between the eyes is often more informative than either value alone. Binocular amplitude usually exceeds the monocular values, because convergence drives accommodation, so a lower binocular value points to a binocular problem rather than an accommodative one.

For facility, note which lens is slow: difficulty clearing the minus lens points to trouble stimulating accommodation, difficulty clearing the plus lens to trouble relaxing it. Low counts both ways indicate general infacility.

When it is used

The test is used for near vision symptoms: blur at near, headache with close work, fatigue while reading, losing place on the page. It suits children and students with reading difficulty, alongside convergence and oculomotor testing.

It is used after concussion, where accommodative problems are common, as a baseline and follow-up during accommodative therapy, and to judge whether a near addition suits a patient who is not yet presbyopic.

Limitations

Push-up amplitude overestimates true amplitude: the target subtends a larger angle as it approaches and the blur endpoint is subjective, so blur is reported after accommodation has already failed. Push-down and minus lens methods give lower values, so compare like with like.

The screen task uses a size ladder in rem units at no fixed viewing distance, so the smallest size read is a screen size, not an amplitude in dioptres and not a facility in cycles per minute. Compare it within one patient on the same display. The dioptric value comes from the distance at the moment of blur, so an estimated distance carries its error into the value.

Screen print size, contrast and the accommodative cue from a self-luminous display differ from a printed near card, so the two are not interchangeable. A dim room widens the pupil, reduces depth of focus and moves the blur point.

Facility needs a physical flipper lens and a clock. The screen times nothing, so the clinician flips the lens and counts.

Validated status means this implementation is considered ready for clinical use on this platform. It does not mean a published study has shown equivalence to a near rule or a printed card.