Also called: Cortical Visual Impairment, Blindness
Vision loss, or a reduction in eyesight, is a symptom that involves a reduction or loss of a person’s ability to see. It can range from having blurred or double vision to compete blindness. The impairment can be temporary or permanent, and may occur suddenly or develop over time. The type of vision loss experienced depends on its cause.
A wide variety of conditions can cause vision loss. These include physical injuries to the eye, eye disorders or diseases, certain medical conditions (e.g., diabetes) and genetic disorders. Certain infections and adverse side effects from some medications may also cause vision loss.
Neurological causes of vision loss typically involve damage, disease or disorder of the optic nerves (one of the 12 pairs of cranial nerves) or parts of the brain associated with eyesight. A variety of neurological diseases can cause this type of damage, including:
- Head injury
- Brain tumors
- Interruption in flow of blood and oxygen to the brain (e.g., stroke)
- Cranial blood vessel problems (e.g., cerebral aneurysm)
- Optic nerve problems (e.g., inflammation associated with multiple sclerosis)
A number of additional symptoms may accompany vision loss, depending on the cause. Dizziness and a loss of balance are the most common symptoms that occur with vision loss. Ataxia, eye pain and headaches may also occur.
Treating vision loss involves treating its cause. Treatments that may be used for neurological causes of vision loss include medications and surgery. However, vision loss due to brain or nerve damage often cannot be reversed. In these cases, treatment often focuses on controlling a patient’s symptoms and developing skills to adapt to vision loss. A number of treatment methods may help, including specialized training and use of mobility aids and/or voice-generating devices.
In many cases, vision loss cannot be prevented. This is especially true for vision loss that results from neurological causes. However, when vision loss is caused by a preventable condition, taking steps to avoid developing the condition may be advisable in order to preserve vision.
About vision loss
Vision loss, or a reduction in eyesight, is a symptom that can vary in severity. It may range from difficulty in seeing things clearly (e.g., blurred or double vision) to complete blindness. Vision loss may occur suddenly (e.g., after a stroke or traumatic head injury) or develop gradually (e.g., certain degenerative diseases such as multiple sclerosis). Vision loss can also be temporary or permanent in duration. The type of vision loss experienced depends on the cause.
Vision loss can occur due to a wide variety of injuries or disorders of the eye. However, neurological causes typically involve damage, disease or disorders of the optic nerves or the parts of the brain associated with eyesight. In these cases, the onset, duration and severity of vision loss is related to the type, location and extent of brain or nerve damage.
The ability to see is a complex process. It involves light entering the eyes through the cornea (transparent surface of the eye). The iris (colored portion of the eye) controls the amount of light that passes through the opening of the pupil (the black center of the iris) by causing the pupil to close more in bright light and open more in dim light (dilate). As light is allowed in, the layer of tissue at the back of the eye called the retina sends nerve signals along the optic nerves, which are transmitted to the brain to create a visual image.
The shape of a person’s eye is often responsible for what is commonly referred to as types of vision impairment, but are better described as refractive errors. Refractive errors occur when the eye is unable to correctly bend (refract) light entering the eye, causing a blurring of sight. Examples of common refractive errors include myopia (nearsightedness or poor distance vision), hyperopia (farsightedness or poor near vision) and astigmatism (either myopia or hyperopia due to a misshapen cornea). Refractive errors are typically resolved with the use of corrective lenses (e.g., eyeglasses or contact lenses). In some cases, refractive errors develop into eyestrain or amblyopia (lazy eye). In amblyopia, the affected eye is weak and does not transmit proper visual messages to the brain. If amblyopia is left untreated, it can lead to permanent vision loss in the affected eye because the brain will begin to ignore signals coming from that eye.
Vision loss caused by a brain or nerve disorder is a more significant problem than refractive errors because it cannot be corrected with the use of corrective lenses or eye patches. This is true for impaired vision or a complete loss of vision. Neurologically-based vision loss may be called cortical visual impairment.
Different areas of the brain are involved with processing different types of information, including vision. The outermost layer of the cerebrum (the main portion of the brain, divided into right and left hemispheres) is called the cerebral cortex. The cerebral cortex can be divided into the following four areas, each affecting different body functions:
- Frontal lobe (involved in planning future action, speech and controlling movement)
- Parietal lobe (involved with touch, sensing pain and spatial relationships)
- Occipital lobe (involved with vision)
- Temporal lobe (involved with hearing, learning, memory and emotions)
Damage to the occipital lobe, located toward the back of the head, can cause vision loss. This area of the brain is associated with the reception and interpretation of visual stimuli. It processes images seen by the eyes and connects the new images to images stored in memory for identification purposes.
Damage to certain cranial nerves can also cause vision loss. For example, damage to the optic nerves disrupts communication between eye and brain. The eye may transmit signals about an object, but that image may not be properly received by the brain and vision loss is experienced.
In addition, injury or disorder of the thalamus, a brain structure located beneath the cerebrum, may also cause vision loss. The thalamus transmits various types of sensory information (including vision) to the cerebral cortex. Damage to the thalamus can disrupt this process.
People experiencing any type of vision loss should consult their physician, ophthalmologist (physician specializing in eye diseases and disorders) or neurologist. A variety of diagnostic methods can be used to identify the cause of vision loss.
Other symptoms related to vision loss
Dizziness and a loss of balance are often associated with vision loss. Any type of vision loss that affects a person’s depth perception (ability to determine distances and spatial relationships between objects) may make a person more unstable on their feet. Vision loss can also disrupt the ability of the eyes to monitor the body’s position in space, resulting in a loss of balance.
Other symptoms may accompany vision loss, depending on the cause of a patient’s vision loss. These additional symptoms may include:
- Ataxia (loss of muscle coordination). Some neurological conditions that cause ataxia may also cause vision loss. For example, spinocerebellar ataxia may sometimes cause blindness due to atrophy (wasting away) of the cerebellum.
- Eye pain. This symptom may occur before the loss of vision, or it may occur alongside vision loss (typically with eye movement), depending on the cause. Optic nerve impairment is a common cause of both eye pain and vision loss.
- Headaches. May sometimes occur with vision loss. Neurological conditions such as infections that affect the brain (e.g., encephalitis), blood vessel problems (e.g., temporal arteritis), brain tumors or pseudotumor cerebri can cause both headaches and vision loss. In addition, migraines may be preceded by temporary vision loss, usually in the form of blind spots (scotomas).
Types and differences of vision loss
Generally, vision loss can described as partial (vision is impaired) or complete (a person is unable to see at all). When vision impairment negatively affects a person’s ability to perform daily activities, it is sometimes referred to as low vision.
Vision loss may affect one or both eyes. It can occur suddenly or gradually, and may be temporary or permanent, depending on its cause. Vision loss may also be constant or it may fluctuate, occurring only occasionally.
Types of vision loss that may be experienced include:
- Problems with visual acuity. Difficulty seeing clearly (e.g., blurry vision), or with interpreting what is seen. Normal visual acuity is 20/20. A person with a visual acuity of 20/40 can see at 20 feet what someone with normal vision can see at 40 feet. In the United States, a person may be considered legally blind if they have a visual acuity of 20/200 (with the best possible corrective lenses).
- Double vision (diplopia). When the image from each eye fails to properly merge, two images are created. This can occur due to a lack of muscle control over eye movements. Nerve impingement, as well as swelling or pressure in the area, can also affect muscle functioning.
- Visual field defects. The inability to see everything within a person’s view. For example, homonymous hemianopia is a type of visual impairment in which half of a person’s visual field is missing. A normal visual field encompasses approximately 160 to 170 degrees of objects in front of a person. Having a visual field of 20 degrees or less may qualify a person as legally blind in the United States.
- Blind spots (scotomas). These are dark areas within the visual field in which nothing can be seen.
- Eye movement problems. Vision impairment occurs due to involuntary eye movements when trying to maintain a steady gaze.
- Eye misalignment (strabismus). Vision impairment occurs because eyes do not point in same direction (e.g., crossed eyes). It may affect one or both eyes, and it may be occasional or constant. It can affect a person’s depth perception, causing dizziness or a loss of balance. Chronic misalignment can lead to lazy eye (amblyopia), which, in turn, can lead to permanent vision loss.
Potential causes of vision loss
Vision loss can have a wide variety of causes, including physical injury to the eye, eye disease, malnutrition, certain medical conditions (e.g., diabetes which can cause diabetic eye disease, or retinopathy), genetic disorders (e.g., cerebral palsy) and infections (e.g., AIDS). Vision loss may also be related to age. For example, macular degeneration (disorder that affects the retina of the eye) is a leading cause of vision loss in Americans 60 and older, according to the National Eye Institute. Cataracts (clouding of the eye’s lens) are another common age-related cause of vision loss.
Neurological causes of vision loss are those that involve injury, disease or disorder of the brain or nerves – especially the optic nerves. Basically, anything that causes damage or dysfunction in these areas can result in vision loss, including:
- Head injury. Traumatic head injury can damage the parts of the brain associated with a person’s sense of sight or the actual eyeball. Auto accidents, falls or sports injuries may cause these types of head injuries. Injury may also occur as the result of certain types of eye or brain surgery. Vision loss that follows a traumatic head injury usually appears suddenly.
- Brain tumors. Tumors, whether benign or malignant (cancerous), can press on areas of the brain or optic nerves, which can cause vision loss.
- Interruption in the flow of blood and oxygen to the brain. Experiences such as stroke, transient ischemic attack (mini-stroke), heart attack or near-drowning can prevent oxygen and blood from reaching the brain. This can result in temporary or permanent vision loss that may affect one or both eyes. In these instances, the vision loss occurs suddenly.
- Cranial blood vessel conditions. This may include vasculitis (inflamed blood vessels), cerebral aneurysm and temporal arteritis (inflammation of the temporal artery, located beside the eye and over the temple area). These conditions provide inadequate levels of nutrients to nerves, which can harm the optic nerves and brain and cause vision loss.
- Optic nerve problems. The optic nerves carry information from the eyes to the brain. Problems with these nerves can result in vision loss. Examples include optic neuritis (inflammation of the optic nerve) and optic neuropathy (damage to optic nerve, also known as optic nerve atrophy).
Optic neuritis may be caused by infection or certain diseases such as multiple sclerosis (MS). It is usually temporary and resolves without treatment. Retrobulbar neuritis (inflammation of the part of the optic nerve immediately behind the eyeball) is a type of optic neuritis that may be accompanied by eye pain and frequently occurs in people with MS.
- Vision loss due to optic neuropathy cannot be recovered because, unlike the nerves of the peripheral nervous system, optic nerves (part of the central nervous system) are extremely limited in their ability to regenerate after injury. Brain tumors, stroke and glaucoma (high eye fluid and pressure that damages the optic nerves) can cause optic neuropathy.
A wide variety of neurological diseases and disorders may cause damage to the brain or nerves that can result in vision loss. These include:
- Batten disease, Jansky-Bielschowsky disease, Kufs disease
- Mitochondrial myopathy (a type of myopathy)
- Olivopontocerebellar atrophy (a type of multiple system atrophy)
- Pseudotumor cerebri
- Tay-Sachs disease
- Tuberous sclerosis (a type of neurocutaneous syndromes)
- Wernicke-Korsakoff syndrome
- Machado-Joseph disease
If the neurological condition is degenerative, any resulting vision loss tends to appear gradually, over time, rather than suddenly.
Certain infections may also cause vision loss. These include meningitis, encephalitis and cytomegalovirus (a virus in the herpes family that is a cause of pneumonia) infection. In addition, adverse reactions to many different medications can affect vision, including antihistamines (common in cold and allergy medications), anticholinergics and some blood pressure medications. Contrary to popular belief, watching too much television, reading in low light, or looking at a computer screen for many hours do not cause vision loss.
Treatment and prevention of vision loss
Some cases of vision loss may improve over time without treatment. In other instances, treating vision loss typically involves addressing the cause – if it can be treated. Corrective lenses (e.g., eyeglasses or contact lenses) or eye surgery are used to treat many types of refractive errors, forms of vision impairment caused by deformed parts of the eye.
Possible treatments for neurological causes of vision loss may include the use of medications (e.g., corticosteroids to reduce inflamed cranial nerves or blood vessels) or surgery (e.g., brain tumor removal). Recent research indicates certain medications used to slow the progression of multiple sclerosis may also treat vision loss associated with that disease. Studies are also being conducted aimed at developing medications to slow or reverse vision loss associated with aging (age-related macular degeneration).
In many cases, treatment goals focus on controlling vision loss to the extent possible and helping patients adapt to the loss. Treatment methods may vary, depending on the type, extent and cause of vision loss. Treatment options may include the use of:
- Eye patch. Placing a patch over one eye may help lessen the effects of double vision, or eye misalignment (strabismus, amblyopia).
- Head-scanning motion. Learning to move the head from side to side can help a person with field of vision defects to see more.
- Large print, adjustable lighting. Use of large-print materials (e.g., books, large font size on a computer), as well as environments with good lighting, may make reading easier for people with visual acuity problems.
- Braille, voice-generating electronic devices. Learning to use a system of raised letters (Braille) can provide an alternative to reading by sight for people with vision loss. In addition, a wide variety of electronic devices (e.g., computers, clocks, oven timers, calculators) can provide audio information for people with vision loss.
- Mobility aids. Canes may be used by people with vision loss in order to avoid obstacles while walking. These are usually swung in a low sweeping motion in the direction a person wishes to travel. In some cases, guide dogs trained to lead people who are blind around obstacles may also be used.
Psychological counseling may also be recommended for people with vision loss. It is common to experience grief over the loss of vision, and speaking with a trained professional can help lessen stress and possible feelings of isolation.
In addition, patients with vision loss may be taught certain strategies or methods of negotiating obstacles while walking, such as when crossing a room or a busy street. Patients may also receive help in improving their other senses (e.g., hearing, touch) to help compensate for their vision loss.
In many cases, vision loss cannot be prevented. This is especially true of vision loss that results from neurological causes. When vision loss is caused by a preventable condition, taking steps to prevent the condition may also help prevent vision loss from occurring. These steps may include:
- Genetic counseling. Adults wishing to have children may undergo genetic counseling to understand the risks of passing on any genetic conditions that may cause vision loss to offspring.
- Controlling blood sugar (glucose). By controlling their glucose (e.g., through use of insulin or other medication, exercise, diet), people with diabetes may be able to prevent vision loss caused by the disease.
- Protection against trauma. Vision loss caused by head injury may be prevented by wearing seat belts while traveling in a car, and wearing appropriate protective head gear while participating in certain exercises (e.g., skateboarding, riding a bicycle or motorcycle) or contact sports.
- Regular eye exams. Visits to an ophthalmologist or optometrist are important for early identification and treatment of any potential eye disorders or diseases that may cause vision loss.
Questions for your doctor regarding vision loss
Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to vision loss:
- What type of vision loss am I experiencing?
- What do you think caused my vision loss?
- Did my vision loss result from brain damage?
- Could any of my current medical conditions or medications have contributed to my vision loss?
- What type of tests will you need to perform to confirm your diagnosis? How do I prepare for these tests?
- Is my vision loss likely to get worse over time?
- Is my vision loss permanent or might it be reversible?
- How do you recommend treating my vision loss? What are the risks or side effects associated with this treatment?
- How can I maximize my ability to function despite my vision loss? Is there specific training you’d recommend for me, or devices that may benefit me?
- Is there any way I can prevent a worsening of my condition?