|Year : 1999 | Volume
| Issue : 4 | Page : 233-236
Visual outcome in optic nerve injury patients without initial light perception
A Agarwal, AK Mahapatra
Department of Neurosurgery, All Institute of Medical Sciences, New Delhi, India
Department of Neurosurgery, All Institute of Medical Sciences, New Delhi
Source of Support: None, Conflict of Interest: None
Purpose: To assess the prognosis for recovery of vision in patients with blindness due to head injury, and to analyse the predictive value of visual evoked potential (VEP).
Methods: One hundred consecutive patients with unilateral/ bilateral blindness as a result of minor head injury were studied with regard to their visual status, CT scan, MRI scan and serial VEPs. Steroids were given to those presenting within one month of injury, 5 patients among them received methyl prednisolone. Transethmoidal decompression was done in 6 patients.
Results: Visual improvement was recorded in 23 patients. Initial VEP failed to reveal any wave in 29 patients and was abnormal in 71. All the 14 patients in whom VEPs were repeatedly normal, irrespective of initial VEP status, showed varying degrees of visual improvement and none of the 15 patients with persistently negative VEPs showed visual improvement.
Conclusion: Recovery of VEP from no response to abnormal wave or abnormal wave to normal VEP were indicators of relatively good visual prognosis. Overall, 23 patients showed visual improvement, but did not return to normal. Mode of injury, CT findings and timing of surgery did not influence the outcome.
Keywords: Optic nerve trauma, VEP, light perception
|How to cite this article:|
Agarwal A, Mahapatra A K. Visual outcome in optic nerve injury patients without initial light perception. Indian J Ophthalmol 1999;47:233-6
Optic nerve injury is uncommon after closed head trauma and is reported in 0.5-0.6% of the cases. The serious nature of the vision loss, the often complicated circumstances of the injury and the crossing of traditional medical speciality boundaries have led to interest in the study of indirect optic nerve trauma. Despite recent comprehensive reviews which provide an excellent background and summary of the current knowledge of indirect optic nerve injuries, many questions remain as to the natural history, pathophysiology and management of traumatic optic neuropathies. There are only a few studies which have dealt with visual evoked potentials (VEP) in the evaluation of post-traumatic blindness. This study has been carried out to assess the prognosis for recovery of vision and to analyse the predictive value of VEP in patients with initial unilateral/ bilateral negative light perception (NLP) vision, as a result of minor head injury
| Materials and Methods|| |
One hundred consecutive patients presenting to the Department of Neurosurgery with unilateral or bilateral blindness as a result of minor head injury over a 4-year period (Jan 1992 to Dec 1995) were studied. The mode of injury and the interval between the injury and the arrival to our hospital were recorded. The patients' visual status was evaluated at initial presentation. CT scan of the head and the orbit was performed in all the patients. MRI was performed in four patients. VEPs were performed with the Nicolet Compact Four machine (Madison, USA) using light-emitting diode (LED). The VEPs were classified as normal, abnormal or absent, depending on the wave form. VEPs were performed on the day of presentation or in acute stage within 24 hours of admission, then repeated 2-3 times in the first week, and then weekly for the next 3-4 weeks. When a patient presented after 2 weeks, two consecutive negative VEPs were considered significant.
Patients were prescribed corticosteroids if they presented within a month of injury. Patients presenting within 48 hours of injury received intravenous dexamethasone 4 mg 6 hourly for 48 hours, followed by oral prednisolone therapy 40 mg a day for one week, tapered over the subsequent 2 weeks. In 5 patients intravenous (IV) methyl prednisolone 30 mg/ kg body weight was injected as bolus and subsequently 5mg/ kg body weight IV infusion was continued for 47 hours. Patients who improved minimally and then remained static were subjected to transethmoidal microsurgical optic canal decompression. Patients who progressively improved or those who did not show any improvement were not operated. Three patients were operated as part of the randomised double-blind study conducted by the International Optic Nerve Trauma Study (IONTS) between March 1994 and March 1996.
| Results|| |
Of the 100 patients included in the study, 93 were males and 7 were females. The majority of the patients were young; 36% were between 21 to 30 years [Table - 1]. Road traffic accident was the most common cause of injury (73 patients). Eighteen patients were found to have sustained injury as a result of fall from a height, and majority of them were children. The mean duration between injury and presentation was 30 days, (1 day -1½ years); the median duration was 15.5 days. Sixty patients presented within 3 weeks of injury and of these patients, 22 showed visual improvement.
Bilateral nerve injury was recorded in two cases. CT scans were abnormal in 26 patients [Table - 2]. The most common finding was that of an orbital wall fracture, which was found in 22 patients. The CT findings could not be always correlated with the outcome. MRI scan was performed in only four patients. Optic nerve laceration was seen in one patient. The findings in the remaining three were normal. Use of methyl prednisolone or IV dexamethasone did not lead to a significant difference in visual recovery.
Initial VEPs were abnormal [Figure - 1] in 71 and absent [Figure - 2] in 29 patients. Of the 29 patients with initial absent waves [Table - 3], 15 had persistently absent wave in follow-up VEPs and in 8 patients follow-up VEPs showed abnormal waves. The remaining 6 patients developed normal waves and all had improvement in vision. VEP changes preceded visual improvement. Of the 71 patients with initial abnormal VEP, 63 had persistently abnormal waves on sequential VEP Overall, visual improvement was recorded in 23 patients. In 7 patients visual recovery was limited to perception of light and hand movement which was considered insignificant improvement. The remaining 16 patients had useful visual recovery [Table - 4], but did not return to normal. On further analysis, the mode of injury, age of the patient and presence or absence of orbital fracture did not influence the outcome. Similarly, early surgery did not prove to be an important factor in recovery.
VEP was the single most important factor determining the outcome. Initial VEP was absent in 29 and abnormal in 71 patients. Of the 29 patients who had a negative initial VEP, 15 remained persistently negative VEP and none of these 15 patients showed improvement. Of the remaining 14 patients, 8 had abnormal wave in follow-up examinations and 5 showed varying degrees of visual recovery. In 6 patients VEP became normal in course of time and all of them showed visual improvement.
Of the 71 patients who had initial abnormal VEP, 63 continued to have abnormal wave formation on repeated studies and only 4 of these 63 showed some degree of visual recovery. The remaining 8 patients in whom repeated VEPs showed normal waves, had visual improvement. Thus in the total group, 14 patients ultimately had normal VEP and all showed some improvement. In 71 patients VEP was repeatedly abnormal and 9 of these patients (9/71, 12.6%) showed improvement. Thus, improvement of VEP from negative to abnormal wave or abnormal to normal was more predictive of visual improvement.
| Discussion|| |
Optic nerve injury is a rare condition, nevertheless it is important as it could cause significant visual loss and even blindness. In India it is estimated that over 500,000 people suffer from some form of head injury every year. Given a 2% incidence of optic nerve injury in association with head injury, over 10,000 would develop optic nerve injury. Only few large series of optic nerve injury are reported in the literature and all of them have included optic nerve injury in general. We have taken a specific group of patients, those with NLP, and analysed the prognosis for the group, as an independent subgroup.
In the absence of a prospective randomised study, management strategies remain controversial. The literature suggests that spontaneous recovery occurs in 25 to 55% of the cases., The number of patients with NLP vision in these studies were small. Lessel reported a study of 33 patients with indirect optic nerve injury wherein there were 6 patients with NLP and two persons showed improvement. However, the number was too small to contribute to any definite conclusions. Data from uncontrolled studies suggest that high-dose steroids may improve the outcome. However, no prospective study has compared medical and expectant treatment. Megadose steroids reduce CNS oedema, microcirculatory spasm and neural necrosis allowing small nutrient vessels that feed the nerve to regain patency. We have also used steroids with possible benefit to our patients. In the present study use of dexamethasone or methyl predinisolone had a similar effect.
Routine surgical decompression of the optic canal has been recommended by many authors., Fukado has reported over 700 cases. In the initial 400 cases in his series, all improved following surgery. However, the subsequent 300 cases had an improvement rate of only 40%. However, his work suffers from lack of selection criteria and clinical details. The frequency of improvement following surgery ranges from 12-79%.,,,
Our study supports the views expressed by Fujitani et al and Lessel in that associated injuries and fractures do not influence the outcome. Nau et al retrospectively analysed VEP in 14 patients and found the usefulness of an absent VEP in predicting a poor visual outcome. They, however, failed to find a good correlation between positive wave and recovery. Our previous studies,,, had shown that none of the patients with follow-up normal VEP had good recovery. Thus, it proved the role of both positive and absent VEP waves in predicting the outcome. Improvement of negative VEPs or abnormal to normal VEPs was indicative of visual recovery.
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[Figure - 1], [Figure - 2]
[Table - 1], [Table - 2], [Table - 3], [Table - 4]