Validation of an Objective Method for the Qualitative and Quantitative Assessment of Binocular Accommodative Facility

Purpose: Assessing binocular accommodative facility (BAF) enables the evaluation of the interaction between the accommodative and vergence systems, which is relevant for the diagnosis of accommodative and binocular disorders. However, the tests used to assess BAF present methodological caveats (e.g., lack of objective control, vergence demands, and image size alterations), limiting its external validity. This study aimed to (i) develop a new objective method to quantitatively and qualitatively evaluate the BAF in free-viewing conditions, and explore its validity by the comparison with the Hart Chart test, and (ii) assess the inter-session reliability of the proposed method.Methods: 33 healthy young adults took part in this study. We used a binocular open-field autorefractor to continuously assess the magnitude of accommodative response during a 60-sec period, while participants repeatedly changed fixation from a far to a near chart when clarity of vision was achieved at each level. Accommodative response data were used to characterize the BAF measurement in quantitative (number of cycles) and qualitative terms (percentage of times that correctly accommodating or dis-accommodating in each level of accommodation as well as the magnitude of the accommodative change).Results: Our data revealed that the new proposed method accurately counted the number of cycles per minute when compared with the Hart Chart test (p = .23, ES = 0.02; mean difference = 0.18 ± 0.85). The inter-session reliability of the proposed method was demonstrated to be excellent (Pearson r and intraclass correlation coefficient: 0.95 to 0.98) for the parameters obtained with the BAF test.Conclusions: The present outcomes evidence that the proposed objective method allows to accurately assess the frequency and precision of BAF by the combination of the classical Hart Chart test and a binocular open-field autorefractometer. Our findings may be of relevance for the diagnosis and treatment of accommodative and binocular disorders.