Subjective and objective measurement of human accommodative amplitude

In the October 2003 issue, Wold and coauthors¹ compare objective and subjective methods to measure accommodation. They measured accommodation subjectively in method 1 by having patients wear their distance correction (ranging from +2.0 to −2.0 diopters [D]) and then pushing minus trial lenses until they could no longer see the distance chart clearly. The accommodative amplitude was defined as the difference between the distance correction and the power of the most minus trial lens that could be added to it and still allow reading of the distance chart.

However, if the patient is wearing the appropriate distance spectacles, making him or her emmetropic, the accommodative amplitude would simply be the dioptric power of the most minus trial lens that could be pushed. The patient's distance refraction should have nothing to do with the definition of accommodative amplitude.

In a ray-tracing diagram, if 1 patient is a 25-year-old +2.0 hyperope and another patient is 25-year-old −2.0 myope, their distance correction will put the distance focal point on the retina, which becomes the starting point from which to measure the accommodative amplitude. Theoretically, these 2 patients would have approximately the same accommodative amplitude based on their age, but using the author's definition of accommodative amplitude, the +2.0 hyperope automatically has 4.0 additional diopters of accommodative amplitude. (When prescribing an add for a pseudophakic patient, we do not give a −2.0 myope a +4.5 add and a +2.0 hyperope only a +0.5 add.)

Thus, the authors' conclusion that “the trial-lens-induced accommodation tended to be more variable when measured subjectively than when measured objectively” should be reassessed after removing the patient's refraction from the definition of accommodative amplitude in the subjective method. Otherwise, the authors' conclusion that objective measurements of accommodation should be used in evaluating new technologies to treat accommodative loss is well taken.

Bryan E. Allf MD

Gastonia, NC, USA