Effect of manipulating the vergence/accommodation and image size mismatches of the ±2D flipper test on the frequency and precision of accommodative facility

Abstract

Purpose: The ±2.00 D accommodative facility test presents several limitations, in- cluding the lack of objective information and inherent characteristics such as ver- gence/accommodative conflict, change in apparent size of the image, subjective criteria for judging blur and motor reaction time. By using free-space viewing con- ditions and an open-field autorefractor to monitor the refractive state, we exam- ined the impact of manipulating these factors on the qualitative and quantitative assessment of accommodative facility. Methods: Twenty-five healthy young adults (24.5 ± 4.5 years) took part in this study. Participants performed three accommodative facility tests (adapted flipper, 4D free-space viewing and 2.5D free-space viewing) under both monocular and binocular conditions in random order. A binocular open-field autorefractor was used to assess the accommodative response continuously, and these data were used to characterise accommodative facility quantitatively and qualitatively. Results: There were statistically significant differences between the three testing methods both quantitatively (p < 0.001) and qualitatively (p = 0.02). For the same accommodative demand, a lower number of cycles was obtained for the adapted flipper condition in comparison with the 4D free-space viewing test (corrected p-value < 0.001, Cohen's d = 0.78). However, this comparison did not reach statisti- cal significance for qualitative measures of accommodative facility (corrected p- value = 0.82, Cohen's d 0.05). Conclusions: These data provide evidence that the qualitative assessment of ac- commodative facility is not influenced by the inherent limitations of the ±2.00 D flipper test. The use of qualitative outcomes by incorporating an open-field au- torefractor allows examiners to increase the validity of the accommodative facility test in both clinical and research settings.