A brain injury can be devastating to the body and its sensory organs. The eyes are no exception.
Acquired Brain Injuries and Nerve Palsies
- Acquired (Oculomotor) III Nerve Palsy
The third cranial nerve can be injured directly or indirectly by compression from a subdural haematoma. The third nerve supplies 4 of the 6 extra- ocular eye muscles. It is also responsible for innervating the pupil and eye lid. Often with injury to the third nerve a person can devlop an eye that turns out and down. They can also have a ptosis (droopy eyelid), and dilated pupil.
The issue with resolving third nerve palsies is the way they resolve. As the nerve innervates so many muscles, regeneration can often be directed incorrectly, with the nerve innervating the wrong muscles. For example, a person may look to one side, the nerve will supply the muscle responsible for pulling the eye in, but it will also send messages to the lid to elevate and the pupil to constrict.
- Acute (Trochlear) IV Nerve Palsy
Acute fourth nerve palsies are usually the result of head trauma. The trochlear nerve is subject to damage even following minor trauma due to the nerves anatomy. It is thin and stretches a fair distance in the brain meaning it is more susceptible to injury. Following minor head trauma damage to the fouth nerve can result in transient blurring of the vision. More substantial trauma can lead to double images being percieved as well as torsional disturbances of the visual field. This is due to the loss of innervation to the Superior oblique muscle, which is designed to move the eye down and intort the eye.
- Trauma induced (Abducens) VI Nerve Palsy
Trauma is a common cause of VI Nerve palsies. The nerve innervates the lateral rectus muscle which is responsible for turning the eye out. When the muscle looses its innervation it looses its ability to turn the eye out. Thus an in-turning eye presents.
Acquired Brain Injuries and Field Loss
Injury to different parts of the brain can cause vision loss in entire sections of a persons field of vision. This is due to the anatomy of the visual pathway, which beigins at the optic nerve, and ends at the occipal lobe at the very back end of the brain. Damage along any area of this visual pathway can cause visual field loss.
- Temporal Lobe Lesions
The temporal lobe is responsible for auditory processing. It is also important for speech and vision. The optic tract, a part of the visual pathway, passes through the temporal lobe. Injury to this area of the brain can result in visual field loss occuring in the superior part of a persons field of view, see picture below.
- Parietal Lobe Lesions
The anterior portions of the optic radiations run throught the parietal lobe. If this area is damaged field loss will occur in the inferior quadrant of a persons field of view, see picture below.
- Occipital Lobe Lesions
The occipital lobe contain the posterior portion of the optic radiations. Damage to these areas can result in a hemianopia (loss of one entire half of a persons visual field). In this instance there may or may not be an area of macular sparing. This means the fibres that represent the most sensitive part of vision, may not be affected. The picture below shows the ‘sparing’.
Acquired Brain Injuries and Cortical Blindness
Cortical blindness is a unique phenomenon in which partial or total blindness occurs due to a loss of the brains ability to translate images. All the areas of the visual pathway, including the eyes, appear normal, but the occipital cortex, the area of the brain responsible for interpreting visual input, no longer functions.
People with cortical blindness often deny that they are unable to see. Often they need to be prompted with simple questions, such as “how many fingers am I holding up?” before they recognise there is an issue. On examination the pupils will still respond to light (constrict when a light it shone on them), and eye health will appear normal.
How we can help
Our optometrists willl work as a part of a multidisciplinary team, along with neurologists, occupational therapists and rehabilitation specialists to manage patients who have acquired brain injuries.
An optometrist will:
- perform a comprehensive eye health assessment
- do a refraction to measure the eye’s power
- complete a low vision assessment to gage what would be necessary to maximise poor vision
- perform a visual field assessment to detect loss of any peripheral vision and advise patients in regard to eligibility for driving
- complete an assessment of focusing ability
- perform an assessment of binocualr vision function to identify the existence of single vision and the degree of depth perception
- complete an assessment of how any visual loss is affecting balance, posture and general movement
- examine eye hand co-ordination
- assess vision processing and vision perception
What management options are available at an optometrist?
- spectacles for clear and stable vision
- spectacles for near tasks such as reading and computers
- prisms ground into glasses to help treat symptoms of double vision, and provide greater stability of balance and movement
- patching (total or partial) to assist with maintaining comfort
- Vision therapy to imporve focusing, eye movements, eye co-ordination and hand eye coordination
- REFERRAL to VISION AUSTRALIA for low vision services
- REFERRAL to other specialist capable of assisting with the holistic management of the condition
For more information on eye health and eye conditions or to find your local Eyecare Plus optometrist visit: www.eyecarevision.com.au
About optometrists:
Optometrists are experts in vision care who diagnose, manage and treat a wide range of vision problems, eye diseases and ocular conditions. By prescribing spectacles, contact lenses, vision aids and other treatments, optometrists help their patients maximise and retain good vision for life.