Hemianopsia

What is Hemianopsia?

Hemianopsia, or the loss of half of your visual field, is a condition that can occur due to suffering from a stroke, having a brain tumor or any traumatic injuries to the brain. It makes it rather hard for those affected to move around their environment, read, and drive. This can significantly impact your productivity and overall health due to the interference with your normal vision.

To understand this better, consider how we see things. When our eyes take in any visual information, it is sent through optic nerves to the optic chiasm, a part in the brain where information from both eyes meets. When this information gets there, it gets divided into two parts – information from the right and left sides of your field of vision. This naturally allows the formation of an image in our brain that we perceive as our surroundings.

Any damage or injury to these pathways can be categorized into three types. It could be prechiasmal, meaning it affects the optic nerve and can lead to blindness in one eye. Or it could be chiasmal, meaning it affects the optic chiasm and disrupts the division of information, leading to loss of vision on both sides. Lastly, anything affecting areas beyond the chiasm can interfere with the optic pathways or primary visual area in the brain. Depending on the particulars of the damage, this might lead to homonymous hemianopsia (losing the same half of the visual field in both eyes) or quadrantanopia (loss of one-quarter of the visual field).

Homonymous hemianopsia, or having a pupillary defect, implies that the damage is in the optic tract. This condition affects a part of your visual pathway that controls your pupil’s response to light. If you have this condition but can still see within your central visual field, the damage is likely to the primary visual cortex, the area in your brain responsible for processing visual information.

In a nutshell, it’s crucial to be aware of any changes in your vision, as hemianopsia can often be overlooked. Therefore, if you’re at risk for a stroke or brain tumors, or have had a traumatic brain injury, make sure you’re regularly checked for any visual issues. Notably, more than half of the patients with this condition can recover within a month if the cause is an ischemic stroke. However, other therapies are also available to help patients adapt to their environment. Prompt evaluation and accurate diagnosis can help identify treatable causes like strokes.

What Causes Hemianopsia?

Homonymous hemianopsia is a type of vision loss that affects either the right or left side of the eyes’ vision. This problem can occur if there’s any injury along the pathway that transfers information from our eyes to our brain. In some cases, the vision loss can be complete, meaning it affects the entire side of the vision. There are also incomplete variations of this vision loss, which are further divided into two types—congruous and incongruous. In congruous homonymous hemianopia, the vision loss in the two eyes is similar in shape, depth, and size. If the patterns are not identical, these are categorized as incongruous.

This type of vision loss can be caused by many factors, such as stroke, bleeding in the brain, head injuries, tumors, certain surgeries, and neurological conditions like multiple sclerosis, Alzheimer’s disease, and epilepsy. In some rare cases, severe high blood sugar can cause temporary homonymous hemianopia, as shown in a patient with diabetic ketoacidosis.

A specific type of homonymous hemianopia, called ‘macular-sparing,’ often preserves the central 5 to 25 degrees of the visual field. This usually happens when the back half of the brain’s visual processing area (occipital region) is partially unaffected. This type of vision loss is more common in stroke patients because of the blood supply patterns in the back of the brain.

Bitemporal hemianopsia is another type of vision loss that primarily affects the outer sides of your field of vision in both eyes. This condition often happens due to a growth or injury impacting the optic chiasm—a critical point in your brain that receives visual information. Some lesions, such as pituitary adenomas, craniopharyngiomas, and meningiomas, are often associated with this type of vision loss. Additionally, trauma to the base of the skull, frontal bone fractures, or blood vessel abnormalities could also lead to bitemporal hemianopsia.

Binasal hemianopsia is a rarer form of vision loss that typically impacts both sides of your field of vision and can be caused by conditions like aneurysms, fluid accumulation in the brain (hydrocephalus), tumors in the brain, neurosyphilis, and high pressure inside the skull.

Risk Factors and Frequency for Hemianopsia

Hemianopsia, or the loss of half of the visual field, can occur for various reasons. In adults, strokes are often the main cause, accounting for roughly 70% of cases. On average, these patients are 58 years old. On the other hand, in children, tumors contribute to 39% of cases, diseases affecting blood flow to the brain contribute to 25%, and injuries account for 19%. In people with a condition known as homonymous hemianopsia, strokes mainly affect the part of the brain responsible for vision in 54% of patients. Additionally, 33% have impact on the paths connecting the eyes and the brain, and 6% on the nerve tracts transferring visual information.

In cases of homonymous hemianopsia that are not related to stroke, the damage can occur in various parts of the visual pathway. In particular, 24% affect the part of the brain that handles vision, 31% impact the paths linking the eyes and the brain, 19% involve the nerve tracts carrying visual information, and 25% affect multiple parts of this pathway.

• In adults, strokes are the main cause of hemianopsia, accounting for about 70% of cases.
• The average age of these patients is 58.
• In children, tumors, diseases affecting brain blood flow, and injuries are the main causes, accounting for 39%, 25%, and 19% of cases respectively.
• In people with homonymous hemianopsia due to stroke, 54% have the part of the brain responsible for vision affected, with other portions of the visual pathway affected in other patients.
• In non-stroke-related homonymous hemianopsia, damage can happen in different parts of the visual pathway.

Lastly, a type of tumor known as a pituitary adenoma is the most common cause of bitemporal hemianopsia, a condition where there is vision loss in the outer or side fields of vision in both eyes. Research suggests that around 16.7% of people have these tumors. Also, the most common cause of homonymous hemianopia, another type of vision loss, with macular sparing, is problems in blood flow to the back of the brain or damage to this area.

Signs and Symptoms of Hemianopsia

Visual field defects can result in vision problems that patients might not be able to clearly explain. They could talk about losing sight in one eye or having general visual issues like dimmed vision or trouble reading. Whenever there are such visual complaints, a complete physical examination should be carried out promptly. This is especially vital when certain neurological emergencies are suspected, typically indicated by sudden changes in mental state or the appearance of new focal neurological issues. In these cases, immediate support should be given for the patient’s vital signs as well as their airway, circulation, and breathing.

Every person complaining of visual issues should be given a test to measure visual acuity as well as a thorough neurological exam. The examiner should specifically focus on examining the pupils and testing the visual field. If the patient has a defect in their visual field that affects both their temporal fields, it’s likely that there’s damage to the optic chiasm. On the other hand, if the visual field defect is homonymous (i.e. affecting the same field of vision in each eye), it indicates that there is damage to the areas beyond the optic chiasm, like the optic tract, optic radiations, or the primary visual cortex in the occipital lobe. If the patient has a pupillary defect plus homonymous hemianopsia (half blindness), it suggests localised damage to the optic tract.

Moreover, if the patient has homonymous hemianopsia and their macula (the central part of the retina) is not affected, it points toward damage to the primary visual cortex. Despite having sight loss in one half of their vision, central vision is preserved, even up to 25 degrees. This is a crucial finding as it suggests a blockage in the posterior cerebral artery, but allows for the patient to still read fluently. There are two main theories for why this “macular sparing” happens.

• Dual Representation of the Macula in Each Hemisphere: Even when one occipital lobe is lost, the remaining lobe can still provide central vision for the blind half of the visual field. The core of this theory hinges on the fact that certain retinal ganglion cells project to the wrong hemisphere. These cells stimulate neurons in the an area of the brain, the striate cortex, with receptive fields on the same side, forming the basis of this theory.
• Dual Perfusion Theory: A more widely accepted theory suggests that blood flow from the middle cerebral artery can still circulate to the occipital pole, where the macula is represented, despite a blockage in the posterior cerebral artery. Neuroimaging even shows the preservation of the occipital pole when the patient has macular sparing.

Besides severe loss in their visual field on the side opposite their brain lesion, patients with homonymous hemianopsia may also display other interesting phenomena:

• Anosognosia: patients may not even realize they have a visual field defect.
• Blindsight: Despite losing vision in a certain part of their field of vision, patients may unconsciously retain some basic visual abilities in their blind field.
• Ipsilesional Visual Field deficits: Patients may suffer from subtle vision loss on the same side of their vision field as the brain lesion without being aware of it.
• Visual Hallucinations: These can occur in the blind field. However, patients may not even realize that their perceived visualizations aren’t real.

Testing for Hemianopsia

Testing your field of vision

There are a few ways doctors may test your field of vision, which simply means checking how much you can see around you without moving your eyes or your head. Two common methods are:

Confrontation testing: This is a straightforward test where you sit about 1 to 2 feet away from the doctor and cover one eye. While focusing your other eye on the doctor’s eye, the doctor will move a finger from the edge of your field of vision towards the center. As soon as you see the movement, you say ‘yes.’ This test gives the doctor a rough idea of the size and shape of your field of vision, and it can generally detect bigger vision issues. But, it could miss smaller ones as it only has a sensitivity of 35% to 74% (sensitivity here means the ability to correctly identify people who do have a condition).

Formal visual field perimetry: This second test is more detailed and sensitive than the first one. It can reveal specifics about the size, shape, and type of any vision loss. It’s usually done with special equipment that tracks your eye movements while you’re looking at different lights or images. This is considered essential for people with any brain condition that could affect vision.

Understanding the Cause of Vision Problems

Beyond testing your vision, your doctor will also want to figure out what’s causing any problems you have. Some imaging tests like MRI or CT scans are used beautifully here. They allow the doctors to look closely at different parts of your brain and trace the path of the signals from your eyes to your brain. This is important because any damage or disease along this path could affect your vision.

If the cause of your vision problems looks like a stroke and time is of the essence, your healthcare team will probably quickly do some other tests based on guidelines designed to help with stroke management.

Additional Testing

In some cases, your doctor may need to conduct additional tests. For example, an electroencephalography (EEG) can help the doctor check if seizures might be causing your vision problems.

Blood tests can look for high blood sugar (hyperglycemia) and other diseases. If you need contrast for your imaging studies, your doctor may test your kidney function beforehand, because the contrast can sometimes harm the kidneys.

In the case of a possible stroke, clotting tests may be necessary before giving medicines designed to break up clots.

If your doctors are considering a diagnosis of multiple sclerosis, you may need a lumbar puncture (also known as a spinal tap). This test involves collecting a small amount of fluid from around your spine to look for signs of the disease.

Remember, while this might sound quite complicated, your doctors and healthcare team are trained to perform these tests and interpret the results. They’ll guide you through the process and explain the findings in a way that you will understand.

Treatment Options for Hemianopsia

After examining you physically and considering your imaging scan results, your doctor will determine how to best treat your condition. A condition such as cerebral infarction or a brain hemorrhage will require a specific treatment plan. Your doctor may even consult with specialists in neurology and neurosurgery when necessary. In cases where there are mass lesions or signs of increased pressure within your skull, you might need to be admitted to the hospital for medical or surgical treatment.

Patients suffering from vision impairments may not be fully aware of how their condition limits them; this could affect activities like driving. In the United States, each state has its own laws that determine how much vision a driver must have. The doctor, who is looking after a patient with visual impairments, has a responsibility to evaluate if the patient meets the legal requirements to drive and to discuss this with the patient. The American Academy of Ophthalmology provides a summary of each state’s vision requirements. A holistic approach, comprising visual training, visual assist devices, occupational therapy, and psychological support, can boost a patient’s recovery. Techniques such as visual scanning and compensatory training can improve treatment effectiveness.

The goal of rehabilitation therapy is to help patients adapt to new visual limitations, improve awareness, and manage any associated neglect. Rehabilitation can involve several techniques:

1. Compensation: Patients learn to rely on their remaining, healthy visual functions.
2. Substitution: Patients adjust their surroundings to fit their visual limitations.
3. Restitution: Patients undertake training to redevelop impaired visual abilities.

Some patients may benefit from devices like hemianopic mirrors or prisms, which can alter the perceived visual field. These tools move the peripheral image toward the front of your eye, helping you spot potential hazards. However, these devices can occasionally create confusion or distort vision and are not recommended for use while driving.

If you have difficulties reading due to homonymous hemianopsia (loss of vision in the same area in both eyes), a simple trick like placing a ruler or finger under the text you’re reading can help. For some individuals, learning to read vertically can also be useful. Computer programs can provide guided exercises to help train your eyes to make small rapid movements into your blind field, improving reading speed and reducing scanning mistakes.

There are also restorative methods, which aim to expand your visual field by stimulating parts of your brain next to the blind area. Such methods often involve visual-auditory stimulation therapy that uses your brain’s multi-sensory architecture to restore visual sensitivity. In fact, research shows that this type of therapy could help restore vision in patients with hemianopsia, enhancing their ability to perceive and articulate visual stimuli.

Furthermore, biofeedback training can improve your visual function and overall quality of life. This therapy helps you gain better control over your eye movements and alter the focus of your vision, leading to improved visual acuity, contrast sensitivity, and reading speed.

What else can Hemianopsia be?

When trying to diagnose hemianopsia, which is a condition where a person experiences blindness in half of their visual field, doctors look at a variety of possible causes related to where the problem seems to originate and the underlying reason it happened. Various conditions could be behind hemianopsia, such as:

• Stroke or cerebral infarction
• Bleeding in the brain or intracranial hemorrhage
• Aneurysm
• Mass lesions, like primary or metastatic tumors
• Pituitary adenoma, which are tumors in your pituitary gland
• Craniopharyngioma, a type of brain tumor
• Meningioma, which is a tumor of the brain membranes
• Central nervous system lymphoma or other primary cancers
• Altitudinal hemianopia, a type of vision loss
• Trauma or injury
• Inflammatory conditions, including demyelinating disorders that affect the nervous system
• Severe hyperglycemia or high blood sugar levels
• Degenerative neurological conditions
• Migraine
• Transient ischemic attack, also known as a mini-stroke
• Seizure or status epilepticus, a dangerous condition where seizures last too long or come too close together
• Immunoglobulin G4–related disease, a systemic disease that affects various organs

What to expect with Hemianopsia

Suffering vision loss after having a stroke often points to a challenging outlook, with recovery rates fluctuating significantly between 17% to 67%. Some research studies suggest that only 18% of patients blinded in half of their field of vision (a condition called “homonymous hemianopsia”) regain their vision within about a month of the incident that caused the stroke. On the other hand, some studies report that anywhere from 46% to 67% of these patients will spontaneously recover within a month of having a stroke.

However, as more time passes, the chances of recovering vision decreases, with the possibility of regaining sight becoming notably low after 6 months.

Patients who have lost sight in both their left and right fields of vision due to pituitary tumors (a condition called “bitemporal hemianopsia”) usually see improvements in their vision in 79% to 95% of instances after undergoing surgery to remove the tumor. However, the degree of this recovery may depend on a variety of factors, including the thickness of their retinal nerve fiber layer, the severity of the pre-surgery visual impairment, how long they have been experiencing visual symptoms, tumor size, the extent of the surgery, and the patient’s age.

A recent study looking into how patients adapt to visual field loss after a stroke showed that this adjustment process varies significantly from individual to individual. The study found the success of this adaptation is influenced by several factors, including the results of a mobility assessment course and the level of vision loss suffered in the lower field of vision. The researchers recommend using this mobility assessment course as a way of evaluating a patient’s movement and scanning abilities during the rehabilitation of patients experiencing half-field vision loss.

Possible Complications When Diagnosed with Hemianopsia

People with hemianopsia – or loss of half the visual field in one or both eyes – can face a variety of challenges. These challenges can greatly affect their day-to-day life.

Challenges might include:

• Difficulties maintaining balance
• An increased chance of falling or getting injured
• Loss of independence
• Problems with reading
• Trouble scanning visually
• Higher risk of experiencing depression
• Difficulty finding employment

All these factors can significantly impact a person’s quality of life.

Preventing Hemianopsia

Hemianopsia is a condition where you lose half of your field of vision. In adults, the most common cause is a stroke, followed by brain tumors and injuries to the brain. In children, the primary cause is brain tumors. Often, this condition can go unnoticed by both patients and healthcare workers. If you have any symptoms related to your nervous system, or if you’re having difficulties reading or with your vision, it’s important to have a formal visual field test. Everyday activities such as reading and driving can become challenging due to Hemianopsia, and it may increase your risk of getting hurt, falling, or becoming depressed.

For over 50% of patients, this condition improves on its own within the first month after suffering an ischemic stroke. If you’re living with Hemianopsia, treatment will mainly involve learning how to manage and adapt to the circumstances. The effectiveness of treatments specifically aiming to restore vision is still under discussion among experts.

It’s crucial that you understand how to reduce the risk of having a stroke. This includes controlling high blood pressure, managing diabetes, keeping cholesterol levels in check, treating vascular disease, and quitting smoking. Additionally, if you have Hemianopsia, your ability to drive needs to be evaluated due to safety concerns. Since this condition could potentially affect your work and leisure activities, it’s also important to monitor for signs of depression.