Disorders of Binocular Convergent Fusion and Stereoscopic Space Perception Following Acquired Brain Damage – Treatment and Neuroanatomical Implications

III ABSTRACT The unified and three-dimensional percept we perceive through the two of our eyes is the result of multiple interacting functional and neural processing stages in the visual brain. They range from convergence eye movements and sensory merging of the two disparate monocular images (binocular convergent fusion) up to an elaborated stereoscopic percept containing spatial depth (stereoscopic vision). Acquired disorders of binocular convergent fusion and stereoscopic vision of varying degrees are frequent sequels following damage to the brain, e.g. after a stroke or traumatic injury, among others. Typical symptoms of fusion impairment are blurred vision and/or diplopia after short periods of sustained binocular near space activities like reading or PC-work, usually accompanied by asthenopic symptoms like fatigue or eye pressure. Since fusion is a prerequisite of stereoscopic vision, difficulties in tasks that require precise judgements in visuo-spatial depth like grasping or taking staircases can occur. As a result, fusion impairment and associated deficits in stereoscopic vision can result in plain difficulties in almost all visual near-space activities of daily or vocational routines. The probably most severe deficit in stereoscopic vision can manifest in a complete failure to process or integrate any visual depth cues from the monocular images provided by our eyes resulting in a completely " flat " visual world (" flat vision "). In the context of the constantly aging population alongside with an increased number of survivors from brain damage requiring reintegration in daily-and work-life, it appears unexpected, that no systematically evaluated treatment options have been available for these conditions so far. This circumstance surprises even more with regard to neurorehabilitation techniques in other visual domains, as there exist well-evaluated restitutional treatment strategies using perceptual (re-)learning paradigms grounding on repetitive systematic visual practice. Consequently, the principal objective of this thesis was to evaluate in three consecutive studies the effectiveness of a novel binocular vision treatment designed for patients with acquired binocular convergent fusion and stereovision impairments of differential etiology: Study 1 and Study 2 addressed the potential effects of this treatment in three different patient groups with impairments in convergent fusion and stereoscopic vision after cerebral hypoxia (Study 1), stroke and traumatic brain injury (Study 2). It was examined whether repetitive and ABSTRACT IV graded training of binocular convergent fusion with dichoptic devices could lead to improvements in binocular fusion and stereoscopic vision and to which extent the possible benefits might transfer to functionally relevant binocular …