Negative Visual Phenomena

Measuring visual acuity (VA) is a foundational component of the ophthalmic examination, enabling clinicians to assess the integrity of the visual pathway and localize potential pathology. VA is typically assessed using distance and near optotypes such as the Snellen chart, with adjustments including pinhole testing to differentiate refractive errors. For patients unable to read charts, alternative measures such as counting fingers or light perception are used. Factors affecting VA include refractive errors, contrast sensitivity, pupillary size, and spherical aberration. Pupillary assessments, including direct and consensual responses and the swinging flashlight test, further assist in detecting any relative afferent pupillary defect. Confrontation visual field testing and Amsler grid methods help identify defects along the visual pathway. A systematic anterior-to-posterior approach is required for clinicians to evaluate for pathological etiologies affecting VA. In this chapter, a case study of left homonymous hemianopia following an occipital stroke illustrates a component of the post-chiasmatic visual pathway and how visual field deficits affect function and quality of life. Rehabilitation with optical devices such as yoked prisms may improve daily functioning, though outcomes vary. Accurate VA assessment is critical in diagnosing, monitoring, and managing ocular and neuro-ophthalmic disease.