Stroke And Vision: What's The Connection?

Vision loss is a common occurrence after a stroke, with around 65% of stroke survivors experiencing changes to their vision or vision loss. The impact of a stroke on a person's eyesight depends on the individual and the areas of the brain that have been affected. Strokes occur when a part of the brain is starved of oxygen and nutrients, causing brain cells to die. This can result in a variety of vision problems, including visual field loss, eye movement problems, and visual processing issues. While some people may regain their vision over time, others may experience long-term changes or require vision therapy and other treatments.

Homonymous hemianopia

The damage that causes homonymous hemianopia usually occurs in the occipital lobe, which is the most posterior part of the brain. The right half of the brain has visual pathways for the left hemifield of both eyes, and the left half of the brain has visual pathways for the right hemifield. Therefore, an injury to the right side of the brain will affect the left visual fields of each eye, and vice versa. The more posterior the cerebral lesion, the more symmetric the homonymous hemianopia will be.

People with homonymous hemianopia may feel like they are unable to see out of one eye, but in fact, both eyes are affected. For example, when reading, words and sentences disappear when they are in the missing visual field. Similarly, people may appear to have only half a face. This condition can make daily tasks such as reading and watching television very challenging. It can also affect a person's ability to get around, especially in crowded or unfamiliar places, as they may miss obstacles on their side of the field loss.

Visual hallucinations may accompany homonymous hemianopia, especially if it occurs suddenly as a result of a stroke. These hallucinations are not related to a psychiatric disorder and may improve over time. In addition, people with homonymous hemianopia may experience visual neglect, where they not only do not see to one side but also do not attempt to move their eyes or head to look in that direction. This further increases the risk of bumping into things and getting into accidents.

While some recovery from homonymous hemianopia is possible, it usually occurs within the first few months after a stroke. Glasses or contact lenses generally do not help with vision loss due to this condition. However, prism lenses can be used to shift images from the non-seeing to the seeing the visual field. Eye patches can also be used to block one image if the person is experiencing double vision. Additionally, scanning techniques can be taught to compensate for the missing field of vision.

Quadrantanopia

Yes, it is possible to lose eyesight after a stroke. Vision problems are quite common following a stroke, with almost two-thirds of people experiencing some form of visual impairment. This is because a stroke occurs when a part of the brain is starved of oxygen and nutrients, which can affect the visual pathways of the eye and impact vision in different ways.

There are two types of quadrantanopia:

• Homonymous inferior quadrantanopia: This type of quadrantanopia is characterised by a loss of vision in the same lower quadrant of the visual field in both eyes. It is caused by a lesion affecting the inferior optic radiations, known as the temporal pathway or Meyer's loop.
• Homonymous superior quadrantanopia: This type of quadrantanopia results in a loss of vision in the same upper quadrant of the visual field in both eyes. It is caused by a lesion affecting the superior optic radiations, known as the parietal pathway.

Individuals with quadrantanopia may modify their behaviour to compensate for the disorder. For example, they may tilt their head to bring the affected visual field into view. Drivers with quadrantanopia may drive slower, use more shoulder movements, and corner and accelerate less drastically than typical individuals.

The prospects of recovering vision in the affected field are generally bleak, with most people who experience vision loss after a stroke not fully recovering their sight. However, some recovery is possible, usually within the first few months after the stroke. Techniques such as scanning training and optical aids can help individuals make the most of their remaining vision.

Eye movement control

• Impaired eye movements, where one or both eyes cannot move correctly, affecting the ability to follow moving objects or move between objects. This can lead to blurred or double vision (diplopia).
• Constant or unsteady eye movements, known as nystagmus, which can cause moving images, double vision, and difficulty focusing.
• Drooping of the eyelid (ptosis) or an enlarged pupil, caused by nerve damage.
• Dry eyes, which can be a result of problems with the nerves of the eyelid, the facial nerve, or the muscles of the eyelid.

To address these eye movement control issues, treatment options such as prisms, occlusion, or patching may be used. Prisms are effective when the double vision does not change significantly as the patient looks around. Occlusion involves partially or fully covering one eye to eliminate double vision. Eye exercises are also an important part of rehabilitation, helping to strengthen eye muscles and improve control. These exercises can include directional tracking, near/far focusing, and visual perceptual exercises such as word searches and hidden picture puzzles.

Visual neglect and agnosia

Visual Neglect

Visual neglect is a common visual processing problem that can occur after a stroke. It is characterised by a lack of awareness of things on the side of the body opposite the side of the brain affected by the stroke. For example, if the right side of the brain is affected, the person may be unaware of objects and people on their left side. This can cause them to ignore people, bump into objects, or have difficulty locating things. Visual neglect can also affect a person's perception of their own body, causing them to ignore food on one side of their plate or fail to apply makeup or shave one side of their face. Treatment for visual neglect typically involves training the person to scan their environment and use strategies to increase their awareness of their affected side.

Agnosia

Agnosia is a rare condition, affecting less than 1% of people with neurological disorders, where a person loses the ability to recognise, identify, and name familiar objects using one or more senses. There are different types of agnosia, including visual agnosia, auditory agnosia, olfactory agnosia, and tactile agnosia. Visual agnosia is the most common and well-understood form and can be further divided into two types: apperceptive agnosia and associative agnosia. Apperceptive agnosia is characterised by an inability to perceive the primary characteristics of objects, while people with associative agnosia are unable to recognise objects despite perceiving all their features. People with visual agnosia may have difficulty recognising familiar faces and objects, colours, or their own body parts. Treatment for agnosia typically involves compensatory strategies, such as using other senses to recognise objects or modifying the environment to facilitate recognition.

Dry eyes and light sensitivity

Dry eye is a common issue that occurs when your eyes do not produce enough tears to keep them moist and lubricated, or when your tears evaporate too quickly. Tears are essential for maintaining clear vision and protecting your eyes from irritants. Even though dry eye disease is not typically sight-threatening, it can cause discomfort and disrupt your daily routine.

One symptom of dry eyes that many people experience but don’t understand is sensitivity to light, also known as photophobia. The current understanding is that light sensitivity from dry eye disease can be caused by inflammation of the trigeminal nerve near the cornea or an irregular eye surface from a lack of tears that causes light to scatter when entering your eyes.

If you have dry eyes, you may experience light sensitivity to many types of light, such as sunlight, fluorescent light, incandescent light, computers, or candle flames. Other symptoms associated with light sensitivity include increased discomfort, squinting, and the instinct to avoid bright environments. Additionally, people with increased light sensitivity might find driving at night challenging due to glare from headlights.

There are several treatments available for dry eyes and light sensitivity. The cornerstone of mild dry eye treatment is often the use of artificial tears or lubricating eye drops to supplement your natural tear film and provide relief from dryness and reduce light sensitivity. Your optometrist may recommend preservative-free artificial tears for long-term use to avoid potential irritation.

In cases of moderate to severe dry eyes, your eye doctor may recommend prescription medications such as anti-inflammatory eye drops or medications that stimulate tear production. Lifestyle modifications, such as blinking regularly, taking breaks from prolonged screen use, maintaining proper hydration, and using humidifiers in dry indoor environments, can also help manage dry eyes.

Wearing sunglasses or eyeglasses with special coatings can provide a protective barrier for those exposed to environmental factors that exacerbate light sensitivity and dry eyes, such as glares and wind. Tinted lenses can also help reduce light sensitivity, with some studies finding that glasses with at least one tint color provided symptom relief for 85% of participants with photophobia.

If you notice dry eye symptoms, including light sensitivity, it is important to visit your eye doctor. They can evaluate your ocular health, diagnose the underlying cause, and recommend treatments like intense pulsed light (IPL) therapy and radiofrequency (RF) to help alleviate your symptoms.

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