Where's the Vision? The Importance of Visual Outcomes in Neurologic Disorders: The 2021 H. Houston Merritt Lecture.

Neurologists have long-recognized the importance of the visual system in the diagnosis and monitoring of neurological disorders. This is particularly true since approximately 50% of the brain's pathways subserve afferent and efferent aspects of vision. During the past 30 years, researchers and clinicians have further refined this concept to include investigation of the visual system for patients with specific neurologic diagnoses, including multiple sclerosis (MS), concussion, Parkinson's disease (PD) and conditions along the spectrum of Alzheimer's disease (AD, mild cognitive impairment [MCI] and subjective cognitive decline [SCD]). This review, highlights the visual "toolbox" that has been developed over the past three decades and beyond to capture both structural and functional aspects of vision in neurologic disease. While the efforts to accelerate the emphasis on structure-function relationships in neurological disorders began with MS during the early 2000's, such investigations have broadened to recognize the need for outcomes of visual pathway structure, function and quality of life for clinical trials of therapies across the spectrum of neurological disorders. This review begins with a patient case study highlighting the importance utilizing the most modern technologies for visual pathway assessment, including optical coherence tomography (OCT). We emphasize that both structural and functional tools for vision testing can be used in parallel to detect what might otherwise be sub-clinical events or markers of visual and, perhaps, more global neurological, decline. Such measures will be critical as clinical trials and therapies become more available across the neurological disease spectrum.