Vision Tests For Stroke Patients: What To Expect

Vision is often affected after a stroke, with about two-thirds of stroke survivors experiencing some changes to their vision. The impact of a stroke on vision depends on which area of the brain is affected. The visual pathway is very long and goes from the eyes to the occipital lobe, which is the region in the cerebral hemisphere that processes vision. Since the visual pathway goes through the cerebral hemisphere on each side, a stroke affecting certain areas of the cerebral hemisphere will impact the visual pathway and produce visual field loss.

There are four main types of vision problems that can occur after a stroke:

- Loss of central vision

- Visual perceptual abnormalities

- Eye movement abnormalities

- Visual field loss

It is important to have a comprehensive eye exam following a stroke to identify any vision problems and determine the best course of treatment. Treatment options may include prism lenses, eye patches, eye drops, and adaptations such as using large print and improving lighting.

Visual field loss: the patient may not be aware of missing areas in their peripheral vision and may bump into things

Visual field loss is a common occurrence after a stroke, affecting around half of stroke patients. It can cause a partial loss of vision, typically in peripheral vision, and can occur on the left or right side, in the upper field of vision, in the lower field of vision, or in a combination of areas. This is because the stroke has damaged the vision areas of the brain, preventing the brain from processing images from one area of vision. This is despite the eyes themselves working normally.

The visual field loss will depend on the location of the stroke. Damage to the right side of the brain causes loss of left-sided vision, while damage to the left side of the brain causes right-sided vision loss. The most common type of visual field loss is hemianopia, where the left or right half of the visual field of both eyes is lost. This is sometimes called homonymous hemianopia. Scotoma is another type of visual field loss, where there is a small patch of vision loss, often near the centre of vision.

Some people with visual field loss may not be aware of the missing area of vision. They may only notice it when looking in a mirror and only being able to see one side of their face. They may also bump into things as they are unaware of things happening to one side of them. Visual field loss can make it difficult to get around, particularly in unfamiliar or crowded places.

There are a number of treatment options for visual field loss, including visual scanning training, which encourages patients to look to their left and right sides more efficiently, and widening the field of view with optical aids, such as glasses with a plastic prism in one or both lenses.

Visual perceptual deficits: problems may include neglect of one side of the body, difficulty recognising faces or objects, or issues with colour vision

Visual perceptual deficits, also known as visual processing disorders, refer to problems with the way the brain interprets and processes visual information. While some people are born with these deficits, others develop them as a result of a stroke or traumatic brain injury.

There are several types of visual perceptual deficits, including:

• Colour perception: The ability to accurately distinguish between colours. Some people may experience complete colour blindness, while others may experience specific colour deficits, or find that colours seem duller than before. This can make it difficult to select matching clothes, identify when food has gone bad, or read maps.
• Form constancy: The ability to recognise shapes and objects when viewed from different angles, distances, or sizes. For example, a person with this deficit may struggle to recognise a cup stored upside down or a piece of clothing on the ground.
• Figure-ground perception: The ability to focus on and identify a specific item separate from its background. People with this deficit may struggle to filter out irrelevant objects, for example, when trying to locate a knife in a cluttered drawer.
• Depth perception: The ability to judge how far away something is or the amount of space between objects. This is important for everyday activities such as walking up and down stairs, parking a car, and writing or drawing.
• Motion perception: The ability to interpret movement. This helps with isolating items from the background and judging distance. People with this deficit may struggle to judge the speed of oncoming traffic or play sports.
• Spatial perception: The ability to judge the size, shape, movement, and orientation of objects in space. This involves integrating many components of visual perception.

Visual agnosias are a specific type of visual perceptual disorder where a person loses the ability to identify what they see, even though they may be able to describe some features. For example, a person may have good colour, depth, shape, and size perception but be unable to recognise familiar faces.

Visual perceptual deficits can be improved through vision training, which involves performing specific exercises to strengthen identified visual skills.

Eye movement abnormalities: the patient may experience double vision or blurred vision due to impaired eye muscle control

Eye movement abnormalities are a common occurrence after a stroke, with about 40% of stroke patients experiencing them. These abnormalities can manifest in several ways, including:

• Double vision or diplopia: This occurs when the cranial nerves that control eye movement are affected, resulting in misaligned eyes.
• Blurred vision: This can be caused by impaired eye muscle control, making it difficult to maintain stable focus on objects.
• Wobbly eyes or nystagmus: This condition causes the eyes to constantly move or wobble, making it challenging to focus on objects.
• Inability to move both eyes together: If the nerve control to the eye muscles is affected, one eye may not move correctly, leading to blurred or double vision.
• Impaired eye movements: These issues can affect the eyes' ability to move between objects or follow a moving object, such as someone walking past.

The impact of these eye movement abnormalities on daily life can be significant. Patients may struggle with reading, as it becomes difficult to find the beginning or end of a line of text. They may also have trouble with general mobility, as their ability to look around quickly is compromised.

Treatment options for eye movement abnormalities include:

• Prisms: These are used to help eliminate double vision and are effective when the size of the double vision does not change significantly as the patient looks around.
• Patching one eye: Occluding one eye can also be an effective solution for double vision, as it makes it easier to see, although using only one eye can cause some difficulty.
• Exercises: In some cases, exercises can help improve eye movement control, such as when patients have difficulty moving their eyes to look at objects held close to their face.

Visual hallucinations: the brain generates images in the missing area of vision, which can be complex or simple patterns

Visual hallucinations are a common occurrence after a stroke, affecting around two-thirds of patients. These hallucinations can be distressing and have a detrimental impact on functioning, so it is important to seek immediate medical attention if they occur.

Visual hallucinations can manifest in various forms, ranging from simple patterns, streaks, or blurs of colour to more complex images of animals or people. These hallucinations occur due to the brain generating images in the missing areas of vision. The brain fills in the gaps left by visual field loss, often with complex or simple patterns. This phenomenon is known as a cortical release phenomenon, where the loss of normal visual input leads to spontaneous activity in the visual cortex.

The visual pathway is long, extending from the eyes to the occipital lobe in the cerebral hemisphere, which is responsible for processing vision. When certain areas of the cerebral hemisphere are affected by a stroke, it can result in visual field loss. Patients may notice missing areas in their peripheral vision, and in some cases, profound loss of vision in both eyes.

Visual hallucinations can also be associated with specific conditions or disorders. For example, they are a common symptom of Lewy body dementia, Alzheimer's disease, Parkinson's disease, and migraine headaches. Additionally, certain drugs, infections, and medical conditions can induce delirium, which is characterised by confusion, an inability to focus or think clearly, and hallucinations.

It is important to note that the treatment for visual hallucinations depends on the underlying cause. In some cases, improving vision can help, while in others, medication or therapy may be required.

Visual neglect and agnosia: the patient is not aware of, and does not respond to, things on their stroke-affected side

Visual neglect is a common disorder following a stroke, affecting around half of patients during the first few months after the event. It is characterised by a deficit in attention to stimuli on one side of the body, almost always the contralateral side of the cerebral lesion. This can cause a range of functional impairments, including colliding with door frames, unsafe walking, and difficulty in eating.

Visual neglect can be assessed using a combination of paper-and-pencil tests, behavioural assessment tools, clinical observation, and history-taking. Tests include the line bisection test, the star cancellation test, and the Catherine Bergego Scale.

Treatment options for visual neglect include prism adaptation therapy, visual scanning therapy, and virtual reality-based techniques.

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