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Homonymous Hemianopia

Homonymous hemianopia (aka hemianopsia) refers to an absence of vision towards one side of the visual world in each eye. The damage that caused this problem is in the brain and not in the eyes.

Homonymous hemianopia is a type of cerebral vision impairment, which means that the impairment is caused by processing problems in the brain rather than any structural problem with the eyes. The vision loss is usually right or left-sided.

The vision loss can be due to stroke, brain tumours, obstructed blood supply, bleeding in the brain, or a number of other causes. An individual with microphthalmia may have accompanying birth defects, as microphthalmia is a genetic mutation. Genetics Home Reference states that one-third to one-half of people with microphthalmia have it as a component of a syndrome (range of related birth defects).

Symptoms of Homonymous Hemianopia

Vision is lost on the same side in both eyes. For example right-sided homonymous hemianopia means that vision is lost on the right side in both eyes. There are other types of hemianopsia in which sight is lost in different parts of the field of vision. For example in the outer half of both the right and left side (bitemporal hemianopsia) or in a quadrant of vision in both eyes (quadrantanopia).

It is difficult to explain the sensation of a homonymous hemianopia. People with a right homonymous hemianopia often “feel like” the problem is in the right eye, but checking each eye by itself shows that the right side of each eye is affected. The same holds true for patients with a left homonymous hemianopia.

Figure 1

Figure 2

Affected people may bump into things on the side of the visual field defect. Driving may be particularly problematic:  people may get into accidents as they change lanes because they cannot see oncoming cars or sideswipe objects on that side. Objects on a desk or table may not be seen on the side of the visual field loss, and sometimes even the food on that side of the plate is left uneaten. People need to be particularly careful walking through crowded places and crossing the street.

Visual hallucinations may occur with homonymous hemianopia, especially if it develops suddenly as it would from a stroke. Affected people are often reluctant to mention this symptom but these are not related to a psychiatric disorder and may improve over time..

Visual neglect describes a situation in which certain people with brain injury not only do not see to one side, but also do not even try to move their eyes and head to look to see what is on that side of the world. This increases the danger of bumping into things and getting into accidents. This is a problem related to visual “attention.”

One may simulate what a person sees with a homonymous hemianopia by showing a picture of a scene and then blanking half the scene as shown in Figure 1. The normal part of the brain may “fill in” the blank area with an extension of what it can see. Therefore, these people will not fully realize their problem.

Implications

Hemianopsia can affect a child’s ability to read and how they move around objects. It can impact on learning, independence, and leisure activities. Children with right-sided hemianopsia may have difficulty reading left-to-right efficiently as they cannot see the next few letters or words as they move their eyes along the page. Children with left-sided hemianopsia may have difficulty finding the next line of text or beginning of words.

Children with hemianopsia from birth may be more likely to develop eye movements that help them to read than those who acquire hemianopsia later. Children and adults with a hemianopsia will often adopt a head posture to shift their remaining field of vision more to the middle, which can be helpful for them.

Diagnosis

A complete evaluation of the visual system is recommended. Often included in this evaluation is a visual field test that assesses for any visual field defects.

Homonymous hemianopia may be caused by any disorder that affects the brain, including tumors, inflammation, trauma, but most commonly is due to a stroke in the occipital lobe, the most posterior part of the brain. 

Imaging of the brain by magnetic resonance imaging (MRI) is the most common diagnostic test used to diagnose the location and cause of the brain injury.  (Figure 3.)

Figure 3

Treatment

Attempts to address the symptoms caused by a homonymous hemianopia may be directed at two areas: reading and dealing with the environment. Low vision specialists and vision rehabilitation therapists may be consulted to work on these techniques.

Prisms or mirrors have been used on glasses to compensate for the blind field. These attempt to shift or relocate the visual world so that the vision within the defect is moved over towards an area of spared vision in one eye. These work for some but not all patients with homonymous hemianopia.

More formal attempts to help recover visual field loss using computer assisted programs are controversial. These programs may not actually restore what is lost but instead retrain the brain to move the eyes more to “fill in the blanks” or pay more attention to their blind field.

Some people can learn to make quick, often imperceptible eye movements toward the side of the homonymous hemianopia. This allows them to quickly grasp information from the side of the visual world which cannot be seen. This adaptation can take months to develop.

Prognosis

Recovery depends on the underlying cause. The chance for significant recovery is lower after a stroke (blockage of blood flow to a region of the brain) than after inflammation or a mass has been removed.

Any recovery that occurs is likely to begin soon after a stroke and reach its maximum improvement in the first 3 months and certainly by 6 months, with rarely any improvement occurring after that. If the underlying cause is not a stroke, the potential for improvement may differ. This should be discussed with your doctor.

Sources: North American Neuro-Ophthalmology Society and Peninsula Cerebra Research Unit
Cover photo: Fork in the Road, Vision Rehabilitation Services LLC