Study on the postoperative visual function recovery of children with concomitant exotropia based on an augmented reality plasticity model

ObjectiveThis study aimed to investigate the clinical application effect of an augmented reality (AR) plasticity model on the postoperative visual function recovery of children with concomitant exotropia.MethodsBetween September 2019 and October 2021, 28 patients with concomitant exotropia who visited Shenzhen Children’s Hospital (9 male and 19 female) were enrolled in this study. The average age of the patients was 6.4 ± 1.8 years. Postoperative rehabilitation training was conducted using a personalized AR binocular visual perception plasticity model developed based on the patient’s examination results. After 1 month, 3 months, and 6 months of training, the patients returned to the hospital for examinations of perceptual eye position, static zero-order stereopsis, dynamic first-order fine stereopsis, and dynamic second-order coarse stereopsis to compare the changes in eye position control and stereovision function.ResultsAfter 6 months of eye position training, the horizontal perception eye position of the 28 patients was significantly lower than that before training. The difference in eye position at the first and third months compared with that before training was not statistically significant (1st month: z = −2.255, p = 0.024 > 0.017; 3rd month: z = −2.277, p = 0.023 > 0.017; 6th month: z = −3.051, p = 0.002 < 0.017). The difference in vertical perceptual eye position after training compared with that before training was not statistically significant (1st month: z = −0.252, p = 0.801 > 0.017; 3rd month: z = −1.189, p = 0.234 > 0.017; 6th month: z = −2.225, p = 0.026 > 0.017). The difference in 0.8-m static zero-order stereopsis before and after training was not statistically significant (1st month: z = −2.111, p = 0.035 > 0.017; 3rd month: z = −1.097, p = 0.273 > 0.017; 6th month: z = −1.653, p = 0.098 > 0.017). The 1.5-m static zero-order stereopsis was improved after 1 month, 3 months, and 6 months of training compared with that before training (1st month: z = −3.134, p = 0.002 < 0.017; 3rd month: z = −2.835, p = 0.005 < 0.017; 6th month: z = −3.096, p = 0.002 < 0.017). Dynamic first-order fine stereopsis and dynamic second-order coarse stereopsis were measured in the 28 patients before and after training. Patients 1 and 18 had no dynamic first-order fine stereopsis before training, but both regained dynamic stereopsis after 1 month, 3 months, and 6 months of training. Patient 16 had no dynamic first-order fine stereopsis or dynamic second-order coarse stereopsis before training, but first-order and second-order stereopsis had been reconstructed after 1 month, 3 months, and 6 months of training.ConclusionConcomitant exotropia surgery improved the basic problem of eye position at the ocular muscle level, but the patient’s perceptual eye position and visual function defects at the brain visual level remained. This might partly explain the poor postoperative clinical effect. The AR plasticity model can improve patients’ horizontal perceptual eye position and multi-dimensional stereoscopic function, and its clinical effect warrants further study

Attentional Factors Underlying Binocular Vision Loss in Amblyopia

Amblyopia is a neurodevelopmental disorder of vision that results from abnormal visual experience during early development. In addition to significant vision loss in one eye, individuals with amblyopia experience binocular dysfunction, difficulty with visuomotor coordination and attentional deficits. A key component of the vision loss associated with amblyopia is strong, chronic suppression of the amblyopic eye. Clinically, suppression remains challenging to treat, and is a key obstacle to rehabilitating visual function in amblyopia. This thesis examines whether suppressed visual information from the amblyopic eye remains available for processing within the brain and whether higher-order attentional processing is affected in amblyopia. Emerging evidence suggests that attentional mechanisms may contribute to interocular suppression and vision loss in amblyopia. Across four experiments, the findings from this thesis provide several major insights about amblyopia. Visual information seen only by a suppressed amblyopic eye retains a presence within the brain that may subsequently be used for attentional processing. Attentional mechanisms in amblyopia were found to be intact to some extent and thus can be engaged. Orienting visual attention was effective for targets seen by a partially suppressed amblyopic eye and even for complex face cues. Selective attentional tracking by the amblyopic eye was intact in anisometropic amblyopia but was impaired for strabismic amblyopia. Additionally, the process of attentional disengagement and re-engagement may be impaired during amblyopic eye viewing. Overall, these results demonstrate that the amblyopic eye continues to influence visual perception despite being suppressed under normal viewing conditions. As a result, appropriate refractive correction of the amblyopic eye should be clinically prescribed to optimize image quality for binocular combination. Furthermore, amblyopia may affect how visual attention is allocated between the eyes, providing a therapeutic target to guide future rehabilitative efforts

The adaptive elements of disparity vergence: Dynamics and directional asymmetries.

Vergence eye movements alter the angle between the two visual axes, creating changes in binocular fixation distance. They are primarily stimulated by retinal image disparities, but can also be driven by inputs from ocular accommodation (accommodative-vergence) and perceived proximity (size) changes. Because of these diverse and complex sensory inputs, the neuro-motor substrates that sub-serve vergence control possess robust adaptive capabilities to manage the interactions with other oculomotor systems (accommodation). This adaptive plasticity in vergence allows for a high degree of precision in binocular alignment to be maintained throughout life in the face of constantly changing environmental demands. The precise alignment of each eyes’ fovea is a fundamental requirement for stereopsis and the perception of depth in 3 dimensions. In a significant portion of the ophthalmic clinical population, the adaptive capacities of vergence are reduced or dysfunctional, leading to difficulties focusing clearly and comfortably at near distances such as books, computer screens and other hand-held devices. Furthermore, new wearable technologies such as virtual and augmented reality increase the demand on the adaptive capacities of vergence by drastically altering the congruency of the sensory inputs to vergence. Currently, our understanding of the mechanisms that underlie this adaptive control and their behavioral limits are limited. This knowledge gap has led to conjecture in the literature regarding proper rehabilitative therapies for clinical dysfunctions of vergence control and in the optimal environmental design parameters that should provide comfortable and compelling user experiences in wearable technologies like VR and AR. The inward (convergence) and the outward (divergence) turning of the eyes in response to retinal disparities are controlled by two separate systems and demonstrate significant directional asymmetries in their reflexive response properties. In general, reflexive divergence responses tend to be slower and longer than their convergence counter-parts. It is unclear whether the adaptive mechanisms are influence by these reflexive asymmetries. It is also unknown whether similar directional differences exist in the different adaptive capacities possessed by vergence. The purpose of the following dissertation was to characterize the effects of stimulus direction on the adaptive behavior of disparity-driven vergence eye movements with an end goal aimed at improving rehabilitation therapies for clinical populations with vergence dysfunction and providing valuable insight for the design and future development of wearable technologies like virtual and augmented reality environments. A series of 4 experiments were conducted in order to characterize the effect of stimulus direction and the physiological limits of the adaptive behavior within the two-main disparity vergence motor controllers, fast-phasic and slow-tonic. In each study, binocular viewing conditions were dichoptic, which allowed retinal disparity to be altered while the accommodative and proximity cues were clamped. Such designs create incongruencies between the sensory stimuli to vergence and thus elicits a much stronger adaptive response for observation than would normally occur when viewing real-world objects. Eye movements were monitored binocularly with a video-based infrared eye-tracking system at 250Hz using the head-mounted EyeLink2 system. A total of 14 adult binocularly normal controls and 10 adult participants with dysfunctional convergence control (convergence insufficiency) were recruited for the main studies. 4 controls completed the first two studies, 10 additional controls completed the third and fourth studies while the 10 participants with convergence insufficiency completed the fourth study. The results of this dissertation make four significant contributions to the current scientific literature pertaining to vergence oculomotor control and plasticity. 1) Both fast-phasic and slow-tonic vergence controllers display directional asymmetries in their general behavior and adaptive responses. 2) Reflexive fast-phasic divergence responses in controls tend to saturate at lower disparity-stimulus amplitudes than convergence under specific viewing conditions. This saturation limit is defined when the primary vergence response amplitude and peak velocity are unable to increase when the stimulus amplitude increases, suggesting saturation in neural recruitment and firing rates. Saturated reflexive vergence responses instead recruit an increased response duration (neural firing time) in order to produce larger amplitude responses. 3) Saturation in the fast-phasic divergence mechanism leads to saturation in the speed slow-tonic vergence adaptation. The function of the underlying reflexive fast-phasic response was found to be associated with the adaptive behavior of the slow-tonic mechanism, suggesting one drives the other, which is consistent with model predictions. 4) Convergence responses from individuals with convergence insufficiency are generally indistinguishable from that of the slower divergence responses of controls. These impaired convergence responses lead to impairment of the adaptive mechanisms underlying each fast-phasic and slow-tonic controller. Clinically, these results suggest that rehabilitative therapies for vergence control dysfunctions should primarily target the performance of the fast-phasic reflexive vergence mechanism. This work also suggests that improvements in adaptive capacities of vergence, known to be the mechanism under-pinning symptom reduction in these patient populations, should follow when reflexive fast-phasic responses are normalized. In terms of wearable technology, the generally limited adaptive plasticity demonstrated within divergence responses when compared to convergence in controls, provides a behavioral explanation for the increase in symptoms of discomfort when viewing distant objects in virtual reality environments. Future investigations should seek to determine the effects of other disparity stimulus parameters, such as contrast and spatial frequency on the adaptive behaviors of both fast-phasic and slow-tonic mechanism. Finally, the cerebellum is known to be central to the adaptation of almost every motor system and yet its role in the different adaptive capacities of disparity-vergence control remain unclear. Future studies should aim to characterize these neural structures role in the different vergence oculomotor adaptive mechanisms described here