Stroke-Induced Vision Problems: Understanding The Link

A stroke is a brain attack that occurs when blood carrying oxygen to the brain is interrupted, causing brain cells to die. Vision problems are a common occurrence after a stroke, with about 60-65% of survivors experiencing some form of visual impairment. The type of vision problem depends on the location of the stroke, with the occipital lobe and brain stem being key areas for visual processing. Vision loss can be temporary or permanent, and may manifest as field cuts, blind spots, or scotoma. Other issues include light sensitivity, dry eyes, and problems with eye movement and depth perception. Treatment options include eye tests, glasses, prisms, patching, and visual scanning techniques.

Visual field loss

There are two main types of visual field loss:

• Hemianopia: This is the most common type, where a person loses half of their visual field in both eyes. It can make reading difficult, as words and sentences disappear when they fall within the missing field.
• Scotoma: This is a less common type, where a person has a small patch of vision loss, often near the centre of their visual field.

It is important to have a person's vision checked after a stroke, as visual field loss may not always be obvious. Early diagnosis and intervention are crucial for optimising recovery and improving quality of life.

Eye movement problems

A stroke can lead to a variety of eye movement problems, which occur when the nerves that control your eyes are damaged. This can result in both eyes not working together as a pair, causing difficulties in maintaining stable focus on objects due to blurred or double vision.

Types of Eye Movement Problems

• Impaired eye movements: Difficulty moving eyes between objects or following a moving object, such as someone walking past. This can make reading more challenging and affect general mobility, such as walking outdoors.
• Inability to move both eyes together: If the nerve control to the eye muscles is affected, one eye may not move correctly, resulting in blurred or double vision (diplopia).
• Nystagmus: Constant or rapid eye movements that make it hard to focus on objects and cause moving images or double vision.
• Impaired depth perception: Difficulty judging the distance between objects, which can lead to misjudgments in everyday tasks, such as pouring a cup of tea.

Treatment Options

Treatment options for eye movement problems after a stroke include:

• Exercises: Specific exercises can help improve eye movement control, such as training the eyes to focus on objects held close to the face.
• Prisms: Prism lenses can be added to glasses to improve double vision or allow you to see things to the side if you are unable to look in that direction.
• Eye patching: Covering one eye with a patch can be an effective solution to avoid double vision and improve overall vision.

Visual processing problems

• Difficulty recognising objects, people, colours, or familiar sights in their visual field.
• Trouble reaching for objects or seeing more than one object at a time.
• Visual neglect or inattention, where individuals are unaware of things on their affected side, often caused by strokes on the right side of the brain.
• Visual hallucinations, where the brain generates images in the missing area of vision.

The occurrence of visual processing problems depends on the location of the stroke in the brain. Strokes affecting the occipital lobe, the primary vision centre in the brain, are particularly likely to cause visual processing issues. Additionally, the brain stem, located at the base of the brain, controls eye movements, balance, and the ability to recognise and understand objects. Strokes in this area can also lead to visual processing difficulties.

Other sight problems, including light sensitivity

Light sensitivity, also known as photophobia, is a common symptom after a stroke or mini-stroke (transient ischemic attack, or TIA). It is estimated that sensitivity to bright light can affect between 5-10% of people with TIA, with women possibly having a greater risk. Among those with headaches after a stroke or mini-stroke, 13-30% are likely to experience painful sensitivity to light.

Post-stroke sensitivity to light often occurs with a headache, which is usually a tension-type headache, and other sensory sensitivities, particularly to sound (phonophobia). It can be experienced as pain due to light exposure, along with other reactions such as:

• Headaches or migraine attacks triggered by light exposure
• Eye symptoms like squinting, eye strain, eye pain, and redness
• Avoidance of bright light or a lower threshold for it
• Anxiousness, panic, and other emotional symptoms
• Pattern glare sensitivity, or ocular discomfort when viewing certain visual stimuli

Research has suggested that people who have had a stroke may be more susceptible to pattern glare, which is an extension of their general hypersensitivity to their environment. They experience discomfort when viewing striped patterns and endure elevated levels of visual stress, headaches, eye strain, and photophobia.

The same types of light sources can trigger symptoms, including screens, fluorescent lighting, and bright outdoor light. The presence of post-stroke headaches and/or migraines indicates a lower tolerance for bright light, and they may be negatively affected by specific wavelengths of blue light.

Light sensitivity can be managed by using therapeutic glasses, such as TheraSpecs, which filter the wavelengths of light associated with different brain responses. FL-41 glasses, for example, cut out 480-520nm of light, which is known to trigger or aggravate photophobia. Z-Blue lenses, on the other hand, block a different part of the light spectrum associated with hypersensitivity to flashing lights and repeating patterns.

It is important to get back into the light after experiencing light sensitivity, rather than avoiding it or wearing sunglasses indoors, as this can intensify photophobia over time and lead to negative social and emotional outcomes. Evidence shows that some light, especially natural light, can help reduce fatigue and depression and improve sleep after a stroke.

Other Risk Factors for Post-Stroke Photophobia

One of the biggest risk factors for post-stroke photophobia is the presence of a comorbid condition, particularly persistent headaches after a stroke or TIA. Patients who already have migraines prior to a stroke are at greater risk for developing or having recurring headaches and related symptoms after the attack. There is also evidence that people diagnosed with migraine with aura, particularly women, are generally at higher risk for ischemic stroke.

Dry eye disease has also been linked to negative outcomes after a stroke and can cause light sensitivity.

Hemiplegic Migraine and Stroke

Hemiplegic migraine is a type of migraine with aura that mimics a stroke, including symptoms such as short-term motor weakness, numbness, or paralysis, usually on one side. Although it is not a stroke, it carries an elevated stroke risk. Photophobia is a significant symptom of hemiplegic migraine, occurring at the same rate as other migraine types, with 85-90% of patients affected.

Visual hallucinations

A study by Emre Kumral, Arzu Uluakay and Ilknur Dönmez from the Department of Neurology, Ege University Medical School Hospital, Turkey, found that out of 9560 patients with stroke, 8 (0.08%) experienced CBS following an acute stroke. The hallucinations persisted for more than a month in half of the patients, and no electrographic seizures were recorded during this time. The study concluded that CBS may develop following an ischemic stroke involving the occipital lobe.

Another case study published in Cureus in 2021 described a 68-year-old female patient who presented to the emergency department with complaints of left visual field hallucinations. The patient reported seeing her dog and deceased mother only when looking to her left. Neuroimaging revealed a subacute infarct in the right posterior occipital lobe, and she was diagnosed with CBS. This case highlights the importance of recognizing CBS as a potential complication of ischemic stroke, particularly when patients present with visual hallucinations.

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