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Accommodative amplitude test methods produce differing results
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Objective measurements of accommodative amplitude differed from subjective measurements, according a study recently published in Optometry and Vision Science.
Anderson and colleagues reported that the results and their clinical implications should cause test administrators to consider a change.
Researchers utilized three techniques in measuring monocular accommodative amplitude: subjective push-up, objective proximal stimulated and objective minus lens stimulated. Their study involved 236 participants who were between 3 and 64 years old.
"For all three of these techniques, the subjects viewed an isolated, 1.5-mm tall, black letter E printed on a white background with their habitual correction," they wrote. "This letter size was selected because it was above the threshold acuity size of all subjects (about a 20/40 equivalent for a 40-cm viewing distance) and remained discernable through the minification created by increasingly powered minus lenses for the minus lens stimulated technique."
Results showed that objective amplitudes were lower than the subjective push-up amplitudes at all ages. The discrepancy was largest in the group of participants between 3 and 5 years old.
"Mean objective proximal stimulated amplitudes for the youngest age group were about half of that measured with the subjective push-up test in the same subjects," the researchers stated. "If we consider clinical expectations based on Hofstetter’s formulas, the mean objective amplitudes measured in the present study were less than 9 D across all age bins reported, which is about 56% of the predicted amplitude from Hofstetter’s norms for the youngest age group included in his predicted fits (8 years).
"These data are in agreement with previous reports that the subjective push-up amplitude test grossly overestimates accommodative amplitude in children, as evidenced by objective techniques using either a proximal stimulus or a minus lens stimulus technique," the authors concluded. "It is important to shift the clinical mindset away from the belief that children have the vast accommodative ability suggested by the subjective push-up technique and to consider the implications this has for leaving moderate and high levels of hyperopic refractive error uncorrected."
Disclosure: This research was supported by a Fight for Sight Grant-In-Aid awarded to Heather Anderson and a National Eye Institute Core Grant to the University of Houston College of Optometry. Custom accessories for the Grand Seiko autorefractor for stimulus presentation were designed and manufactured by Chris Kuether through the support of a NEI grant.
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