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| Year : 1999 | Volume
: 47
| Issue : 2 | Page : 92-3 |
Bilateral optic nerve injury.
Mahapatra AK
Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, 110029, India.
Correspondence Address:
Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, 110029, India.
Bilateral optic nerve injury is a rare condition and is reported in 5-6 percent of all optic nerve injuries. However, there is no published series on bilateral optic nerve injury. Analysis of 31 cases of bilateral optic nerve involvement seen amongst 275 patients with optic nerve injury (11.5 percent) is discussed. Road traffic accident which is the most common cause of optic nerve injury, was recorded in 61 percent. Shotgun injury and blast in jury was the cause in 22.5 percent of cases. All the patients except 4 received steroids. Anterior cranial fossa fracture and opacity of paranasal sinuses were recorded in a third of the patients. Visual evoked potentials were recorded in 27 patients. Improvement in vision was noticed in 23 patients (74 percent). However, among the 62 eyes, 39 eyes showed improvement (62.8 percent). Possible reasons for better outcome in bilateral optic nerve injury are discussed.
How to cite this article:
Mahapatra A K. Bilateral optic nerve injury. Neurol India 1999;47:92 |
Indirect optic nerve injury is a rare condition in closed head injury and is reported in 0.5-2% of all head injuries.[1],[2],[3],[4] However, the above mentioned studies did not mention anything about bilateral involvement of the optic nerve. Fujitani et al[5] reported 110 patients of optic nerve injury in whom 113 eyes were involved, indicating some patients with bilateral involvement. Previous studies from our department had shown bilateral optic nerve involvement in 9-14% cases.[6],[7],[8] To the best of my knowledge the present study is the first one in the English literature dealing with bilateral optic nerve injury.
Out of two hundred and seventy five consecutive patients of head injury treated at All India Institute of Medical Sciences, 31(11.5%) had bilateral optic nerve involvement. Their ages ranged from 2 years to 48 years. 21(68%) patients were between 20-40 years of age. Road accident was the most frequent aetiology (61%) followed by gunshot or blast injury combined, which constituted 23% of cases. Four patients had history of fall from a height and one was injured during an assault. All the patients except 3 received corticosteroids. Visual evoked potential (VEP) study was performed in 28 patients. VEPs were normal in 11 eyes, abnormal in 20 eyes and absent in 25 eyes.
X-ray skull and CT scan (head with orbit) were performed in all the patients. MRI scan was performed in 5 patients only. In all the 4 cases of shotgun injury, one or more pellates were seen around the orbit. Optic canal fracture and pellate around orbit was noticed in 4 patients each, 12 cases had fracture of skull. Opacity in paranasal sinuses was observed in 5 patients.
[TAG:2]Results and Follow up[/TAG:2]
All the patients were carefully evaluated and repeated VEPs were performed. Patients were followed up regularly. The follow up ranged from 3 months to 2 years. Overall, 39 eyes out of 62 showed improvement (62.8%). Amongst these 8% had complete recovery. In contrast, among 31 patients 23 showed improvement (74.2%). When compared with our previous studies a better outcome was observed in patients with bilateral optic nerve injury, than unilateral optic nerve injury.
Over the last 30 years, a large number of chapters, reviews and papers have been published on optic nerve injury.[1],[2],[3],[9] Surprisingly there is no mention of bilateral optic nerve injury as an entity. Fujitani et al,[5] for the first time mentioned involvement of 113 eyes in 110 patients. Indirectly, from their study, one can assume the possibility of bilateral involvement in a few cases. However, the significance of bilateral optic nerve injury as an entity, was not discussed. Mahapatra,[6] in a study of 35 children with optic nerve injury, mentioned about 3 patients who had bilateral involvement. Similarly, Mahapatra and Tandon,[7] reported 7 patients of bilateral optic nerve injury among fifty cases of head injury. However, these numbers were small and probably did not merit to be studied as a special group. In another study dealing with 250 patients, Mahapatra and Tandon[8] reported 33 patients with bilateral involvement. Unfortunately, this group was not separately analysed.
The present study appears to be the only study in the English literature dealing with the bilateral optic nerve injury and brings out the clinical profile and outcome. Clinical profile is more or less similar to those of unilateral optic nerve injury, except that more patients were in the age range of 20-40 years and no patient was above 50 years of age.
The most surprising observation in the present study is the outcome. In previous prospective studies, Mahap- atra and his associates reported overall visual recovery in 40-57% cases,[7],[8],[10] which included both unilateral and bilateral cases. This indirectly means that the percentage of improvement in unilateral cases could have been still lower. In the present study, amongst 62 eyes, 39 eyes showed recovery (62.8%), while amongst 31 patients, 23 showed varying degree of visual improvement (74.2%). Thus, there is a significantly higher percentage of visual recovery in patients with bilateral injury.
The exact reasons for the higher incidence of visual recovery are not clear. However, two mechanisms may be responsible. In a person with bilateral injury even if one eye improves, the number of patients improving is 100%. Let us presume two patients with bilateral optic nerve injury show improvement, each only in one eye. Both patients have shown improvement, i.e 2 out of 2 improved (100%). On the other hand out of 4 eyes in 2 patients, only 2 eyes improved i.e. 50% improvement. This mathematical principle also explains higher percentage improvement in bilateral optic nerve injury group. The second explanation is much more scientific. In case of unilateral injury, it has been observed that impact is mostly over the forehead over the eyebrow, temporal area or around the ipsilateral eye. The brunt of impact is on one eye giving a much higher acceleration and deceleration to the side involved, thereby causing more severe injury to the nerve. When the force of impact is in the midline, probably the force is equally distributed to both the eyes, thus reducing the impact of acceleration and deceleration on each eye to half. Thus, in bilateral optic injury, reduced force of impact offers a higher chance of recovery. This mechanism has to be proved by taking a detailed history and finding out the sites and force of impact, and the type of bone fracture etc. in future study.
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