What is Homonymous Hemianopsia?
Homonymous hemianopsia (HH) is a condition that involves loss of vision in the same half of the field of vision in both eyes. To illustrate, if someone has right HH, they would have trouble seeing things on the right side of their field of vision in both their right and left eyes. This condition is most often due to a stroke in adults or tumors or damage to specific parts of the brain in people below 18 years old.
Most commonly, the source of HH is found in the occipital lobe, which is a part of the brain involved in processing visual information. It can also be due to damage to the optic radiations or optic tract, which are parts of the visual pathway that carry visual information from the eyes to the brain.
On the other hand, bitemporal hemianopsia is a different condition that leads to vision loss on the outer (temporal) side of the field of vision in both eyes. This typically happens when there’s a problem at the optic chiasm – the part where the optic nerves from both eyes cross each other.
What Causes Homonymous Hemianopsia?
Homonymous hemianopsia (HH) commonly occurs due to blood vessel damage. Among adults, this is largely caused by strokes or bleeding in the brain (42% to 89% of cases). Other causes include tumors, accidents, medical procedures, demyelinating disorders (conditions that damage the protective covering of nerve fibers), and diseases affecting the nervous system. In children, cancers (39%), strokes (25%), and injuries (19%) are often the root causes.
HH can result from any injury to the retrochiasmal visual pathway, the part of the brain involved in vision. Many disorders can cause HH, including:
– Blood vessel-related: Strokes, blood clot issues, inflammation of blood vessels, anomalies in the connection between arteries and veins, and enlargement of vertebrobasilar arteries, which supply blood to the brain.
– Neurological: Seizures, loss of cells in the back part of the brain, multiple sclerosis (a disease where the immune system attacks the protective sheath of nerve fibers), conditions like sarcoidosis and Alzheimer’s disease, Creutzfeldt–Jakob disease (a rare and fatal brain disorder), and diseases causing progressive loss of mental functions and movement control.
– Infectious: Brain abscess (a pocket of pus), inflammatory conditions affecting the brain and spinal cord, parasitic diseases like toxoplasmosis and cysticercosis, and neurosyphilis, a complication of syphilis infection.
HH can also stem from inflammation-related diseases such as multiple sclerosis and neuromyelitis optica (a disease affecting the eyes and spinal cord), cancers spreading to the brain, lymphomas (cancers affecting immune cells), and other tumors. Medical procedures, radiation treatment, traumatic brain injuries, and shaken baby syndrome are other causes. Metabolic diseases like mitochondrial encephalomyopathy (a condition affecting brain and muscles), lactic acidosis (a build-up of lactic acid in the body), and stroke-like episodes can also lead to HH.
There are also cases of temporary HH, which resolve on their own. These may be because of transient ischemic attacks (mini-strokes), migraines, or seizures linked to the occipital, temporal, or parietal lobes of the brain, and high blood sugar without ketones present.
In a large study, the brain areas where lesions caused HH were found to be mostly the occipital lobe (45%), optic radiation (32.2%), a combination of multiple areas (11.4%), optic tract (10.2%), and lateral geniculate nucleus (1.3%).
Risk Factors and Frequency for Homonymous Hemianopsia
Homonymous hemianopia (HH) affects males and females almost equally, with males slightly more at 52% and females at 48%. The average age of the patients was around 50 years old. HH was a bit more likely to affect the left side of the vision field (55%) compared to the right side (45%).
- The condition was usually not complete, with 62.4% of patients experiencing less than a total loss of half their visual field (referred to as incomplete HH).
- The remaining 37.6% had complete HH, which means they lost an entire half of their visual field, along with splitting of their central vision.
- The most common type of incomplete visual loss was homonymous quadrantanopia, occurring in 29.2% of cases.
- About 46.5% of patients had HH as the only problem, but the rest (53.5%) also experienced motor symptoms, cognitive alterations, or both.
Signs and Symptoms of Homonymous Hemianopsia
Hemianopia or ‘HH’ is a health condition causing people to lose vision in some part of their visual field. Symptoms can vary, with people suffering from two-sided vision loss or in other cases only losing vision in one eye or struggling with reading. Medical tests are necessary for anyone suspected of having hemianopia, such as checking vision sharpness, pupil reactions, eye pressure, and performing a detailed eye exam.
During an exam, the doctor may use a method called confrontation perimetry which is a quick and easy way to check for hemianopia at your bedside. A neurological evaluation is also important to identify the location of the problem in the brain. Often, individuals with hemianopia show signs of a cerebrovascular accident (stroke-like event), such as sudden weakness or numbness on one side of the face, arm, or leg, dizziness, confusion, speech difficulties, and even loss of consciousness at times.
In everyday life, people with hemianopia usually have some reading difficulties. With right hemianopia it’s hard to find the next word while reading, and with left hemianopia it’s tough to find the new line. Reading can be especially difficult for people with right hemianopia due to irregular eye movements, long periods of keeping their eyes in one place, erratic eye movement back and forth, and trouble moving their eyes to the right.
Driving can also be a challenge for those with hemianopia. In countries where cars drive on the right, people with right hemianopia have trouble identifying cars overtaking them. Those with left hemianopia struggle to drive in countries where driving is on the left.
Those affected by hemianopia often face issues walking across the road, staying in their lane while driving and responding to changes in their environment. These problems may lead to an increase in dependency on others, a higher risk of becoming unemployed, and even depression.
Specifically, lesions in the optic tract can cause complete or partial hemianopsia. These can lead to a pupillary defect in the eye on the opposite side of the tract lesion. On the other hand, light falling on the functioning half of the affected eye can cause the pupil to get smaller (constriction), but if light falls on the part of the eye that has lost visual field, it may cause lesser or no constriction at all.
Damage to the optic radiations often results in a complete, contralateral (on the opposite side) homonymous hemianopsia. Depending on the extent of the lesion, the involvement of the optic radiations can induce complex neurological symptoms like aphasia (language problems), seizures, hallucinations, memory complications, or issues with motor coordination.
Lesions in the occipital lobe, the area at the back of the brain responsible for vision, often lead to hemianopia. Its symptoms can differ, the most prevalent being macular sparing which allows a small area of visual field to be spared due to its dual blood supply. When the damage extends to both occipital lobes, it can lead to complete bilateral homonymous hemianopia or cortical blindness which causes patients to be unaware of their impairment. In such circumstances, even the sharpness of vision can be affected.
Testing for Homonymous Hemianopsia
The confrontation visual field test is a common way to check for problems with your eyesight. During this test, you’ll cover one eye and look at an object (usually the eye of the doctor examining you) and then talk about what you see out of the corner of your eye. This test does depend a lot on the person giving it and may not be very sensitive.
There’s also a more high-tech test called the perimetry test, which can be done either manually or automatically. This test is more detailed and tells us about vision loss, how big and what form the affected area takes, and how deep the vision loss is.
If the problem is related to the part of the brain called the parietal lobe, vision loss will be more significant in the bottom half of your vision. There are different kinds of perimetry tests: “Goldmann’s visual field” is used for neurological visual field problems, but it may not be available everywhere. Other kinds, like “Humphrey Matrix frequency-doubling technology (FDT) perimetry (24-2)” and “Humphrey Visual Field Analyzer”, showed no significant differences in their ability to detect a condition known as homonymous hemianopsia (HH), a condition where a person can only see half of what they should. However, one type of perimetry (SAP) may be more sensitive because it catches unusual scattered areas, and FDT isn’t good at detecting issues directly in the middle of the vision field.
It’s also important to note that the simpler confrontation visual field test isn’t great for catching HH, although using a red object might make it more sensitive.
Aside from just identifying issues with vision, anyone experiencing HH should also go for a brain MRI or CT scan. This helps further identify what’s causing the vision problems.
The issue’s location can also be detected by signs like the Marcus Gunn Pupil, a condition where one pupil appears normal but the other dilates unevenly. If this happens alongside HH, it indicates an issue in or before the lateral geniculate nucleus (an important area for vision in the brain) involving the optic tract (the nerve pathways that connect our brain to our eyes). If the issue is the same in both eyes, it’s likely to be located in the back part of your brain. Different visual issues in each eye would usually mean a problem at the front of your brain.
While these are just general guidelines, here’s how some common combinations might look:
- An issue with the left optic tract: Right-sided HH in both eyes, pupil issues on the right side, and a thinned out right optic nerve.
- Issue with the left temporal lobe: Right-sided HH in either eye with a denser superior visual field (called “pie in the sky”), different visual problems in each eye, and no pupillary issues.
- Problem with the left parietal lobe: Right-sided HH in either eye with a denser inferior visual field (“pie on the floor”), different visual issues in each eye, and no pupil problems.
- Left occipital lobe issue: Right-sided HH in both eyes, same visual problem in both eyes, no pupillary defect, and ‘macular sparing’ (partial vision preservation).
- Issue with the anterior medial striate cortex of the left occipital lobe: Loss of wide side field of vision in the right eye with normal vision in the left eye.
Treatment Options for Homonymous Hemianopsia
Treatment for patients with hemianopia, a condition where vision is missing in half of the visual field, often requires the involvement of many health professionals. A common approach to help regain some vision on the affected side involves the use of two prisms placed on the upper and lower parts of a person’s glasses. These prisms are only used in one eye on the same side as the hemianopia. For example, if someone has right-sided hemianopia, the prisms would be placed over the right eye.
The prisms’ base is directed toward the side where the vision is impaired. The prisms allow patients to view objects on their affected side and thus expand their intact visual field while avoiding double vision or “diplopia”. A prism is a type of lens that bends light, and in this case, it shifts the visual image from the blind side into the functioning visual field. There are different types of prisms available and using them might increase the area a person with hemianopia can see quite significantly.
Some options include short segments of prism placed above and below your main line of sight, rigid prisms embedded into the glasses, or even multiperiscopic prisms that widen the visual field even more. Training is required to use these prisms. When a patient notices an object approaching from the blind side, they should turn their head to see it more clearly.
However, using prisms can pose challenges such as reduced clarity of vision, disorientation, difficulty navigating stairs, and trouble reading. Specific training for planned, systematic eye and head movements, along with scanning tactics, can improve mobility and make it easier to find and focus on objects.
Other solutions to aid in restoring vision include visual training, computer-based therapy, and restorative training that specifically targets improving visual functions in patients with hemianopia.
Getting occupational therapy, social support, psychological rehabilitation, and vision loss management are all crucial aspects of treatment for individuals with hemianopia. This could also involve learning how to read with assistance or completing eye movement exercises that improve overall functionality.
What else can Homonymous Hemianopsia be?
When trying to determine the cause of visual field loss, one possibility could be glaucoma. Glaucoma tends to affect your vision along a horizontal line, different from neurological field loss which typically affects vision along a vertical line. For example, if you have homonymous hemianopia, you would experience vision loss on the same side in both eyes. This means if your right side vision was affected, you would notice it in both your right and left eyes.
On the other hand, heteronymous hemianopia means the loss of vision affects different sides in each eye. For instance, in bitemporal hemianopia, you might notice the right side of your vision is impaired in your right eye, while the left side is impaired in your left eye.
What to expect with Homonymous Hemianopsia
The recovery of Hemianopia (partial vision loss or “blindness”) after a brain injury like a stroke can greatly differ from person to person. It essentially depends on the time between the injury and when a vision test was administered. Between 20% to 60% of people with Hemianopia may start to see improvements in their vision within the first month after their injury.
Most people find that their vision starts to get better within the first 3 months. However, it’s less common to see improvements after 6 months. These improvements in vision could be due to the individual’s underlying disease getting better or an increase in the individual’s ability to complete a vision test accurately.
In a study of 254 people with HH, about half to more than half of the participants who were tested within a month of their injury saw improvements in their vision. This is compared to only 20% who were tested 6 months after their injury. It’s interesting to note that even after 6 months, if a person’s underlying disease improves, it can still help their vision. For example, if a person with multiple sclerosis (a disease of the nervous system) sees improvements in their overall health, their vision can still get better.
Possible Complications When Diagnosed with Homonymous Hemianopsia
Besides the problem of not being able to see properly, people with hemianopia (HH) may feel confused and complain of dizziness, spinning sensations, or feeling sick. All these symptoms can increase their chance of getting hurt. The likelihood of falling also increases due to their vision loss.
Preventing Homonymous Hemianopsia
The risk factors for Homonymous hemianopsia (HH), a condition where a person sees only half the field of view, are related to its common causes. The most frequent cause is damage to blood vessels. So, patients should be aware of any factors that increase their chances of suffering a stroke. These factors include hardening of the arteries (atherosclerosis), high blood pressure (hypertension), diabetes, history of smoking, overweight, excessive alcohol consumption, and any past injuries to the blood vessels.
For those already having HH, it’s important to consider the implications this may have on activities like driving. Operating machinery, including a car, with loss of half of your visual field could endanger you and those around you. Rules about driving with such a condition vary from state to state. If your state’s regulations say that your vision isn’t good enough to drive, your doctor should discuss this with you, highlighting the importance of safety.
