A stroke is a sudden interruption of blood flow to a part of the brain, causing brain cells to die quickly from a lack of oxygen and nutrients. Since the brain is the primary center for processing visual information, injury to this area directly affects sight. About 65% of stroke survivors experience some form of visual impairment, ranging from difficulty with eye movement and alignment to significant field loss.
The Neurological Pathway Linking Stroke and Vision
Visual function relies on an extensive network of brain structures, making it vulnerable to stroke damage. The visual pathway begins at the eyes and extends deep into the brain, with the occipital lobe serving as the primary visual cortex where processing occurs. Strokes affecting the blood supply to this lobe can disrupt the brain’s ability to interpret color, shape, size, or recognize objects.
Visual signals travel along the optic pathways, which include the optic tracts and the optic radiation, before reaching the visual cortex. A stroke in the middle or posterior cerebral arteries, which supply these areas, can damage the fibers carrying information from both eyes. The location of the damage determines the nature of the visual problem; a stroke on one side of the brain can affect the visual field of both eyes.
Beyond sensory processing, the brainstem and cerebellum are centers that control the mechanics of the eyes. The cranial nerves responsible for eye movement originate in the brainstem, and damage there can impair the coordination of the eye muscles. This article focuses on strokes affecting the brain, distinguishing them from acute ocular strokes.
Visual Field Loss
Visual field loss is one of the most common sensory deficits following a stroke, involving the loss of a portion of the area an individual can see when looking straight ahead. This condition results from damage to the visual cortex or the optic pathways. The most frequent presentation is homonymous hemianopia, where the same half of the visual field is missing in both eyes.
A stroke damaging the right visual cortex, for instance, causes a loss of the entire left half of the visual field for each eye. A less extensive injury may lead to quadrantanopia, the loss of only a quarter of the visual field. These losses cause difficulty with daily tasks, such as bumping into objects or losing one’s place while reading.
A separate issue is visual neglect, which relates to the brain’s attention and awareness, not sight itself. People with neglect have difficulty noticing or responding to objects on the side opposite their brain injury, even if their visual field is intact. This spatial inattention is a processing problem, often occurring after a stroke in the right side of the brain.
Eye Movement and Alignment Difficulties
A stroke can cause problems with the physical control and coordination of the eyes. These motor control issues stem from damage to the brainstem or the cranial nerves that supply the eye muscles. When the muscles controlling each eye do not work together precisely, the eyes may become misaligned, a condition known as strabismus.
This misalignment results in diplopia, or double vision, because the brain receives two different images it cannot fuse into a single clear one. Double vision is a disruptive symptom, impacting balance, depth perception, and reading ability. About 16.5% of stroke patients experience diplopia.
Another motor control issue is nystagmus, characterized by rapid, involuntary, and rhythmic movements of the eyes. This uncontrolled movement can occur in a side-to-side, up-and-down, or circular pattern and is often associated with strokes affecting the cerebellum or brainstem. Damage to the brain’s control centers can also lead to a gaze palsy, making it difficult or impossible to move both eyes together in a specific direction.
Rehabilitation and Visual Management
While not all stroke-related visual impairments fully resolve, focused rehabilitation helps individuals manage and compensate for their deficits. Recovery occurs most significantly within the first few months after the stroke. The goal of management is to maximize residual vision and improve functional independence.
For visual field loss, vision therapy includes scanning training, which teaches the eyes to make systematic movements into the blind area. This compensatory technique helps a person actively search for information outside their remaining field of vision. Occupational therapists incorporate these strategies to improve mobility and safety.
For those experiencing double vision due to eye misalignment, prism lenses can be added to eyeglasses. These specialized lenses bend light to shift the image from the misaligned eye, allowing the brain to perceive a single image. For severe or changing double vision, an eye patch or temporary occlusion may be used on one eye.