Effects of cortical damage on binocular depth perception

Stereoscopic depth perception requires considerable neural computation, including the initial correspondence of the two retinal images, comparison across the local regions of the visual field and integration with other cues to depth. The most common cause for loss of stereoscopic vision is amblyopia, in which one eye has failed to form an adequate input to the visual cortex, usually due to strabismus (deviating eye) or anisometropia. However, the significant cortical processing required to produce the percept of depth means that, even when the retinal input is intact from both eyes, brain damage or dysfunction can interfere with stereoscopic vision. In this review, I examine the evidence for impairment of binocular vision and depth perception that can result from insults to the brain, including both discrete damage, temporal lobectomy and more systemic diseases such as posterior cortical atrophy.

This article is part of the themed issue ‘Vision in our three-dimensional world’.

Neuro-visual rehabilitation

Despite the fact that almost one-third of patients suffer from visual deficits following brain damage; neuro-visual rehabilitation to compensate for visual field deficits is relatively neglected in the clinical setting. This is in contrast to physio and speech therapies, which are the bread and butter of rehabilitative programs. Likewise, programs that address coping with dementia usually concentrate on language, memory and cognitive skills, but often fail to address the deficits experienced by the subset of patients suffering from progressive cortico-visual dysfunction. Herein, we will review the different approaches to neuro-visual rehabilitation, mainly concentrating on restorative and compensatory treatments. While the first claims to restore vision in the blind visual field, the latter attempts to improve the use of the remaining intact field. These approaches differ in their premise regarding the ability of the adult human brain to adapt following damage, reflecting different attitudes toward the presumed treatment target organ. While restorative therapies claim to reactivate inactive neurons within or around the damaged cortices, compensatory approaches aim to improve voluntary eye movements to compensate the visual loss. We will also briefly discuss the use of optical devices for bypassing the visual deficit as well as the use of the blind-sight phenomena to convert non-conscious visual abilities in the blind visual field into awareness. The various therapeutic approaches will be discussed in the context of patients suffering from hemianopsia and in patients suffering from posterior cortical atrophy. We will argue that of all, the compensatory strategies have shown the most promising results.

Clinical and Psychometric Evaluations of the Cerebral Vision Screening Questionnaire in 461 Nonaphasic Individuals Poststroke

Background. Cerebral vision disorders (CVDs) are frequent after brain damage and impair the patient’s outcome. Yet clinically and psychometrically validated procedures for the anamnesis of CVD are lacking. Objective. To evaluate the clinical validity and psychometric qualities of the Cerebral Vision Screening Questionnaire (CVSQ) for the anamnesis of CVD in individuals poststroke. Methods. Analysis of the patients’ subjective visual complaints in the 10-item CVSQ in relation to objective visual perimetry, tests of reading, visual scanning, visual acuity, spatial contrast sensitivity, light/dark adaptation, and visual depth judgments. Psychometric analyses of concurrent validity, specificity, sensitivity, positive/negative predictive value, and interrater reliability were also done. Results. Four hundred sixty-one patients with unilateral (39.5% left, 47.5% right) or bilateral stroke (13.0%) were included. Most patients were assessed in the chronic stage, on average 36.7 (range = 1-620) weeks poststroke. The majority of all patients (96.4%) recognized their visual symptoms within 1 week poststroke when asked for specifically. Mean concurrent validity of the CVSQ with objective tests was 0.64 (0.54-0.79, P < .05). The mean positive predictive value was 80.1%, mean negative predictive value 82.9%, mean specificity 81.7%, and mean sensitivity 79.8%. The mean interrater reliability was 0.76 for a 1-week interval between both assessments (all P < .05). Conclusion. The CVSQ is suitable for the anamnesis of CVD poststroke because of its brevity (10 minute), clinical validity, and good psychometric qualities. It, thus, improves neurovisual diagnosis and guides the clinician in the selection of necessary assessments and appropriate neurovisual therapies for the patient.