On the controllability assessment of biofeedback eyeglasses used in Presbyopia treatment

In recent years, hybrid biofeedback systems utilizing user-controlled electrically tunable lenses have emerged as potential treatments for presbyopia. However, the controllability of these systems, closely linked to user adaptability, has received limited attention in the literature due to the challenges associated with obtaining a comprehensive system model. In this study, we present the design, implementation, and validation of an innovative experimental setup aimed at researching and evaluating the controllability of such a biofeedback system. Our setup incorporates a novel low-complexity model, considering the brain, natural lenses (e.g., the crystalline lens), and electrically tunable lenses, to establish a fundamental model for hybrid biofeedback systems. This model is developed based on an analysis of biofeedback systems, geometrical optics, and control theory, facilitating the identification of strategies to decouple system dynamics and enable precise controllability analysis. The proposed experimental setup was validated with volunteers, providing evidence that confirms the reliable operation of the biofeedback system. Our approach encourages a shift from conventional qualitative approaches toward quantitative evaluation of biofeedback devices. The proposed model and experimental setup hold the potential to statistically assess the controllability of hybrid biofeedback systems for correcting presbyopia, paving the way for further advancements in this field.