Vision loss after head injury affects a significant number of TBI patients.
You’re about to learn the most common causes of TBI vision loss, along with some of the best treatments for vision problems after brain injury.
Causes of Vision Loss After Head Injury
Vision loss after a head injury typically has two primary causes. Damage to the eye structures themselves or damage to the visual pathways.
These pathways consist of cells and synapses that carry information from the eye to the visual processing centers in the brain. They include the:
- Optic nerve
- Optic chiasm
- Optic tract
- Optic radiations
The nerve impulses from the retina travel down the optic nerve to the optic chiasm. From the optic chiasm, there is a “crossing over” of visual information, so that images from the right eye go to the left visual cortex and vice versa.
After passing through the chiasm, the impulses follow the optic tract and radiations until they reach the visual cortex, which lies in the occipital lobe. The visual cortex then transforms the neural impulses into images.
As you can see, vision is a complex activity involving multiple areas of the brain. Therefore, damage to any part of the visual pathways will cause vision loss.
Types of Vision Loss After Head Injury
Vision loss after head injury can be partial or total and can affect one eye or both, depending on how severe the damage is.
Below are the most common types of vision loss that TBI patients tend to experience.
Visual Field Loss
Example of central vision loss
This condition refers to blindness in certain areas of your vision, also known as your “visual field.”
Visual field loss is categorized by which part of your vision is affected:
- Hemianopsia: Half of your visual field, either horizontally or vertically, is gone.
- Quadranopsia: A quarter of your visual field is lost.
- Homonymous hemianopsia: The same half or quarter of your vision is lost in both eyes.
- Peripheral vision loss: The outer edge of your visual field is lost.
- Central vision loss: The middle of your visual field is lost, but the peripheral vision is fine.
Visual field loss is caused by damage to the visual pathways and certain areas of the brain. The location and extent of the damage will determine how much vision you lose.
For example, lesions on the optic nerve can cause central vision loss, whereas lesions on the optic chiasm typically cause hemianopsia.
Hemianopsia should not be confused with visual neglect after brain injury.
Visual neglect causes a person to lose awareness of an entire side of their vision so that to them, that side doesn’t exist. Whereas, with visual field loss, even though you can’t see your left side, you still know it exists.
Visual Acuity Loss
Visual acuity refers to the ability to see clearly and to focus on an object. Visual acuity loss, therefore, causes blurred vision.
Blurry vision occurs after damage to the retina or the occipital lobe. Fortunately, most cases of visual acuity loss can be treated with glasses and magnifiers.
If the brain damage was mild, sometimes visual acuity will improve on its own once the nerve fibers heal.
Traumatic Optic Neuropathy
Traumatic optic neuropathy can cause both visual field loss and blurred vision, along with several other vision problems.
It typically occurs after an indirect injury to the optic nerve, such as a transmitted shock from an impact to the head. The optic nerve is particularly susceptible to shock waves, meaning that even seemingly mild bumps to the head can cause damage.
On an MRI, traumatic optic neuropathy might not be seen until 3-6 weeks after initial injury, which can make it hard to diagnose.
Symptoms of traumatic optic neuropathy include:
- Partial or complete loss of vision, usually in one eye.
- Blurred vision
- Decreased color vision (dyschromatopsia)
There is no agreed-upon treatment for traumatic optic neuropathy. However, some people do experience spontaneous healing, especially if the damage was mild.
Diagnosing Vision Loss After Head Injury
Diagnosis for vision loss after head injury is often delayed, primarily because doctors are concerned with treating the more urgent, life-threatening injuries first. If the person is unconscious or disoriented, that can also delay diagnosis.
An examination by an ophthalmologist is needed to fully assess a person’s vision loss, but basic tests can be performed by emergency room staff. Some of the exams doctors might perform in the emergency room include:
- Visual acuity tests. These are performed at the bedside, usually by holding a card or newspaper near the person and asking what they see.
- Confrontation visual field test. This checks the ability to see all four vision quadrants by asking if the patient can see the doctor’s fingers in certain positions.
- Funduscopic examination. This test lets doctors see the optic nerve and confirm that the eye is clear of hemorrhages.
Finally, to test for traumatic optic neuropathy, doctors will check the patient’s pupillary response.
If one pupil responds slower than the other when light is shone on it, this is known as relative afferent pupillary defect and it is a strong indicator of optic neuropathy.
Treating Vision Problems After TBI
The good news is there are ways to restore vision loss after a head injury. You can do this through vision restoration therapy.
Vision restoration therapy involves stimulating the edge of your visual field loss with a light on a computer screen. Patients focus on the center of the screen and respond every time they see a light appear somewhere else. Through this process, the brain is able to rewire itself and hopefully expand its visual field.
While this therapy might not restore vision to what it was before your injury, studies have shown that it does significantly improve vision in patients with hemianopsia. Since it is a non-invasive treatment, it might be worth trying.
Patients with visual field loss can also benefit greatly from scanning therapy. This therapy doesn’t restore vision, but it does help retrain your eyes to scan your surroundings more efficiently.
For example, if you experience vision loss in your lower visual field, a vision therapist will teach you to look down with your head to compensate for that loss.
Vision Loss After Head Injury: Conclusion
Vision problems after head injury can be a particularly difficult problem to deal with.
Fortunately, since most vision loss is caused by brain damage, rewiring your brain through vision therapy can help restore some of your vision and teach you effective ways to compensate.
To take part in vision therapy and other treatments for vision loss after brain injury, make an appointment with a certified vision rehabilitation specialist.
Even if vision therapists can’t cure your visual field loss completely, they can help make living with it a little easier.
Featured Image: ©DragonImages