MEM (Monocular estimated method) objectively tests a patient´s accommodative response at the near working distance (usually at 40 cm). This method is valuable in the diagnosis of binocular anomalies or to predict suspected cases of vergence and/or accommodative dysfunction. It is suggested to use test in all young adults, non-presbyopes and especially patients that have a near complaint (astenophia, diplopia, blur vision) or if you suspect accommodative problems such as latent hyperopia or other accommodative spasm.
Equipment and set-up:
- trial lens set
A patient is asked to hold the test at 40 centimetres (you can measure it with a ruler) and binocularly look at the screen. For children the Harmon´s distance (the distance between patient´s elbow and the middle knuckle) is also frequently used. The test is performed under normal room illumination and the patient should wear his habitual near correction. You and your patient´s eyes should be almost parallel, but the test screen should be little bellow the line between the eyes. The retinoscope beam should be oriented vertically. Ask the patient to watch the animation. While the patient is watching, quickly guide the streak across the patient´s left and right eye and try to evaluate the reflex for WITH or AGAINST motion or for neutrality. Do the test a few times on both eyes to be sure,. Estimate the dioptric value required to neutralise the observed motion.
- With motion → plus lens
- Againt motion → minus lens
Confirm the estimate by inserting a lens into the patient´s line of sight (but do not longer than one second) while evaluating the reflex. If the right lens is chosen, neutrality will be spotted. Repeat the same steps for the other eye as well.
Alternativelly you can use Nott Method where you move the skiaskope toward and away from the patient in order to find the neutrality.
- With motion → move closer to the patient
- Against motion → move further away from the patient
At the end measure the distance.
Interpreting the results:
The normal values are between +0.25 D and +0.50 D
All the values higher than +0.75D (lag of accommodation) can show:
- near esophoria
- accommodative dysfunction (paresis, fatigue)
- under-corrected hyperope or over-corrected miope
- higher + dioptres (eg. +2.00) shows presbyopia signs
All the values below +0.25 D (lead of accommodation) can show:
- near exophoria
- spasm of accommodation
- under-corrected miope
With this test we can find heterophoria and also uncorrected refractive error for distance.