Background: Standard accommodative facility testing, using +/- 2.00 D lenses @ 40 cm, stresses a much different proportion of the available accommodation for a 10-year-old patient with a binocular accommodative amplitude of 12 D and a 35-year-old patient with a binocular amplitude of 5 D. This may explain why research using adult subjects has failed to associate reduced accommodative facility with symptoms.
Methods: For 19 adult subjects with normal age-related amplitudes of accommodation, accommodative facility was measured with the standard test (+/- 2.00 D @ 40 cm) and 36 experimental combinations of test distance demand and lens power range, based on percentages of each individual's amplitude. In a masked study. these results were compared to symptom scores, quantified by a 9-item quality of vision questionnaire.
Results: The strongest relation of facility with symptoms was for the 75% distance demand/30% power range (p = 0.0216), with six other combinations also significant. The standard test combination did not significantly differentiate symptomatic from asymptomatic subjects (p = 0.1 515). The combination of the 45% distance demand/30% power range was significantly related to symptom score (p = 0.0315; r = -0.47603).
Conclusion: Amplitude scaled facility testing provides the same percentage test distance and range of amplitude stimulated for all patients. The 45%/30% test combination differentiates symptomatic from asymptomatic subjects better than the standard test (+/- 2.00 D @ 40 cm) and is the one we suggest for future clinical investigation. Care should be taken when testing symptomatic patients over a long period of time, as they may compensate by relying on a predictor operator during the highly repetitive accommodative facility test, thus achieving a more-rapid response.