Traumatic Optic Neuropathy
Traumatic Optic Neuropathy defines a condition in which there is damage to the optic nerve resulting from any trauma or injury to the eye or head.
The mode of injury can be any of the following two types:
1. Direct Optic nerve injury.
2. Indirect Optic nerve injury.
Direct optic nerve injuries usually results from a penetrating eye injury which damages the skull bone socket containing the eye ball (the orbit), or the bone fragments, or any tumor in brain which can directly compress or damage the optic nerve.
An indirect trauma usually results from any blunt trauma of head, which does not directly involve the optic nerve, but the forces are transmitted to the optic nerve, resulting in damage of the nerve.
The optic nerve is the second cranial nerve. There are twelve pairs of cranial nerves (which arise from the brain and not the spinal cord). So the optic nerve also exists as a pair; one nerve for each eye. It is a collection of fibers, and not just a single nerve.
The interesting fact is that each optic nerve, after travelling a short distance, crosses to the opposite side at a point called as the ‘optic chiasma, thus the optic nerve of right eye ends on the left side of brain and that of the left side ends on the right side of the brain. Each optic nerve ends in an area of brain called as the visual cortex, which finally translates the images seen by the eye.
Symptoms of Traumatic Optic Neuropathy
Patient with Traumatic Optic Neuropathy can present with any degree of visual loss depending upon the extent of damage to the nerve and more importantly, the area of the nerve involved.
This is because the optic nerve damage shows different clinical pictures for different areas of involvement. Some patients may even present with complain of loss of color vision (inability to differentiate between different colors).
Most of the patients of traumatic optic neuropathy are males as the incidence occurs mostly after a vehicle or bicycle accident. Other reported cases come after the gunshot wounds, stab wounds, pellets etc.
Symptoms of Traumatic Optic Neuropathy sometimes do not appear immediately after trauma; instead they start to appear several weeks after the injury. On examination of the eye using fundoscope (a specialized instrument used to visualize the inner side ‘back’ of an eye called the retina), the optic nerve appears to be normal; but the damaged optic nerve starts to atrophy is after about 5 weeks.
Diagnosis of Traumatic Optic Neuropathy
Usually the optic nerve damage is missed early on routing ocular examination. Doctors prefer CT scan or MRI (as required) to be done in such patients coming with a history of trauma involving skull and complain of the visual loss afterwards with normal fundoscopic examination of normal optic nerve.
This is because Traumatic Optic Neuropathy occurs due to a damage of the optic nerve that lies behind the globe and fundoscopic examination cannot reveal this kind of damage, as it is the method to visualize the optic disc (the beginning of the optic nerve), which lies on the retina.
Normally the skull X-rays may reveal the presence of any metallic foreign body within the skull or any bony fragments, yet CT scans or MRI give further details involving the extent of hemorrhage, or presence of any other causative factor like any tumor etc. inside the brain.
Visual Field test can be also very helpful in patient with normal appearing optic nerve. This test will show which area of your vision is affected and also doctor can localize the location of optic nerve damage.
Management of Traumatic Optic Neuropathy
Since 1990’s, the traumatic optic neuropathies have been treated medically by the use of steroids.
Although the main treatment lies in surgical procedure, yet steroids have been used in order to improve the condition. But now several studies have been done in this regard and their use for treatment of traumatic optic neuropathy is still carrying many questions.
Now steroids are not used in cases of Traumatic Optic Neuropathy where there is associated traumatic brain injury as well, or in patients who have been brought to the hospital, eight hours after the injury as the use of steroids have been found to produce several complications.
The surgical treatment of traumatic optic neuropathy is aimed at removing the bony fragments or any foreign particles causing the problem, or to decompress the optic nerve at the site where it is damaged with compression on the nerve by any tumor or a pool of blood collected due to bleeding within the brain, or any other such reason, optic nerve damage.
Outcomes of Treatments
The surgical treatment of Traumatic Optic Neuropathy has variable results, depending upon the extent of nerve involved and the damage occurred. However, the role of the surgical treatment cannot be ignored. The concomitant use of the steroids is still being practiced, yet their role is not fully defined.
In the cases of the optic neuropathies where there are involvements of the bony fragments, or metallic foreign bodies, the outcome is very poor as the nerve is directly and severely damaged be them.