|Year : 1989 | Volume
| Issue : 4 | Page : 184-188
VER in optic neuritis
Vimala Menon, Harsh Kumar, Prem Prakash
Dr. R.P. Centre for Ophthalmic Sciences, AIIMS, Ansari Nagar, New Delhi - 110 029, India
Dr. R.P. Centre for Ophthalmic Sciences, AIIMS, Ansari Nagar, New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
A prospective study was carried out on 27 patients with optic neuritis. Besides detailed clinical examination, visual evoked responses (VER) were studied utilising the checker board pattern reversal and flash stimuli. The recording with the 30 minute check size was found to be the most consistent both for the controls and the patients. Flash evoked VER was most useful in determining the wave form in cases with severe disruption of the visual pathways. Neither the implicit time nor the amplitude of the VER could be directly correlated to the visual acuity changes or other clinical parameters. Implicit time offered a more reliable criterion for evaluation as compared to the amplitude in patients with optic neuritis. The VER recording helps in serial follow-up of a patient and can indicate previous attacks suffered by the patient.
|How to cite this article:|
Menon V, Kumar H, Prakash P. VER in optic neuritis. Indian J Ophthalmol 1989;37:184-8
| Introduction|| |
In patients with optic neuritis, the importance of VER over and above the other clinical tests like visual acuity and pupillary reaction have been debated. ,[2 ] The stimulus required to evaluate the patients with optic neuritis is also debated as some consider the checker board pattern to be ideal while others consider to be better. ,,, A similar controversy exists regarding use of smaller or larger check size stimuli. ,,,, While Halliday et al  had found a direct correlation. between VER amplitude and visual acuity, others ,, have not found any such correlation. The percentage of patients reported to have normal VER value after the acute episode is also variable. ,,
We thus undertook a controlled prospective study to evaluate the role of VER and its various stimulus techniques and to correlate it with clinical parameters in cases of optic neuritis.
| Materials and methods|| |
A prospective study was carried out on 27 patients with optic neuritis comprising 14 males and 13 females with age ranging from 9 years to 48 years (mean 24.6 years).They were followed up for an average period of 6 months (range 4 months to 1 year) following the acute attack. Fifteen age and sex matched controls were also studied.
All subjects underwent a detailed clinical examination including visual acuity, colour vision by Ishihara charts, pulilary reactions, and visual field examination by Goldmann perimeter. VER was recorded by the checker board pattern reversal technique utilizing the NIC 1005 clinical signal averaging computer. The patients were seated in a dark quiet room, one meter in front of a TV screen which subtended an angle of 15 osub at the patient's
eye and displayed a checker board pattern of varying check sizes (60 minutes, 30 minutes and 15 minutes of arc reversing at the rate of 1.88 cycles/second). A flash stimulus with appearance disappearance of checker board pattern of 60 minutes of arc was also used as a stimulus. Three silver electrodes were used with the recording electrode at the forehead and the grounding electrode at the mastoid region and hundred responses were analysed for 250 milliseconds each.
The implicit time of the wave form was recorded from the onset of stimulus to the peak of the major positive wave in milliseconds. The amplitude was recorded from the trough preceding the major positive wave to its apex in microvolts.
| Observations|| |
Of the 27 patients, 10 had Retrobulbar-neuritis, 11 had Papillitis, while the rest had Neuroretinitis. Seven patients were affected bilaterally, the left eye being twice as commonly affected as the right eye.
The visual acuity at presentation, the final visual acuity achieved and the relationship between initial and final visual acuity are depicted in [Table - 1].
The final visual outcome was not related to age or sex, while unilateral cases showed better recovery than bilateral cases. Cases of papillitis showed slightly better recovery as compared to others, 81.8% achieving excellent visual acuity at final follow-up. The pupillary reactions were abnormal initially in 26 patients and the abnormality persisted in 2 cases at final follow-up. Colour vision was initially abnormal in all except one and recovered fully in thirteen patients.
The etiology was unknown in majority of patients 16 (59.25%),five (18.5%) were found to be having multiple sclerosis 3 (11.1 %) had viral infection, 2 (7.4%) had associated sinusitis, while 1 (3.7%) had diabetes mellitus. Pain in the eye as an associated finding was recorded in 14 of the 27 patients of which 9 had pain on movement of the eye-ball. At final follow-up, 12 of these 14 cases had visual acuity better than 6/18 while only 8 of the remaining 13 could achieve this. The VER recording obtained from normal persons using 60, 30 and 15 minute check size and the flash stimulus are depicted in [Figure - 1].
[Table - 2] shows VER values of amplitude and implicit time of 30 control eyes and also the difference between the two eyes, for various stimulus patterns used. The results with 15 minutes arc pattern were quite inconsistent and hence were deleted from the study.
The cut-off point for abnormality was taken as 2 standard deviations (SD) above the mean value, thus the criteria for an abnormal VER response were as follows:
1. Absence of a response.
2. Implicit time greater than mean plus 2 standard deviations of control values for a particular stimulus.
3. Implicit time difference between the two, eyes of greater than mean plus 2 standard deviation of control values for a particular stimulus.
The amplitudes were not considered because of the large standard deviation from the mean in the control group.
In the initial recording when most patients had poor visual acuity, identifiable recordings in VER could be made in 45.3% of the eyes with 60 minute check size, 51.5% with 30 min and 60.6% with flash stimuli.
The percentage of eyes showing abnormal VER recording initially and at final follow-up recording was made at 4 months in each case, a time beyond which no case showed any further visual improvement.
[Table - 4] shows mean values of the VER implicit time at initial presentation in patients with optic neuritis which were statistically significant (FpO.01) as compared to the control group, though at the final follow-up this mean value of implicit time had decreased, it still remained statistically significantly different from the control values (p < 0.01)
The VER amplitudes were lower in the affected eyes at initial recording and remained so at the final follow-up but were not statistically significantly different from the control values.
[Figure - 2] depicts a pathological VER in a case of papillitis. Though with the improvement of vision there was reduction in implicit time and increase in amplitude no correlation could be established between the amount of improvement in Snellen acuity and VER parameters.
At the end of follow-up there were 17 cases which had achieved excellent visual acuity (visual acuity better than or equal to 6/9) out of which 13 had also regained normal colour vision. Of these 13 cases with normal colour vision, 9 had abnormal VER but of the 4 cases with persistent colour defects only 1 had defective VER. The common field defects encountered were central, paracentral and centrocaecal scotomas along with peripheral constriction.
There were 11 eyes which had a persistent field defect at the end of follow-up while 16 had regained normal fields. Persistent VER abnormalities were seen in 9 of these 11 eyes and 10 of the 16 eyes.
| Discussion|| |
Our study did not reveal any female preponderance, perhaps reflecting the lesser number of multiple sclerosis patients in this study. 
Initial visual acuity seems to offer a definite clue to the prognosis and these findings are in agreement with the work of Bynke et all while being contradictory to that of others . 13
Patients who presented with pain as an associated findings had a slightly better chance of visual recovery than those without it. This is contrary to the view held by certain other authors. 14,15 It is well known that the pain fibres reside mainly in the dural sheath while the substance of the nerve itself is devoid of any sensation. Therefore, it is possible that any inflammation in the periphery would cause more pain but would affect the central macular fibres much less, thus giving better chances of visual recovery.Therefore, the association of pain could be an indication of perineuritis.
Recovery of visual fields did not correlate with the recovery of VER parameters.
In analysing the VER responses, the implicit time of the major positive peak was the most reliable parameter of study because of its constancy and minimal standard deviation from the mean as seen in the controls. VER amplitude because of its large standard deviation in controls, proved to be an unreliable parameter, which is in conformity with the observations of other workers. ,
The VER recordings, with the 30 minutes check size were more constant and hence only these were used as guidelines for interpreting the pathological cases. The recordings with flash were very inconsistent and had a larger deviation from normal. Even the implicit time values in flash recordings showed a standard deviation of 11 milliseconds. This implies that for a case to be termed pathological we must record an implicit time of more than (96.3 ± 22.0) 118.3 msec. This value throws a large number of pathological recordings into the normal range. The only advantage of the flash recordings was that in cases with severe visual diminution (i.e. at initial presentation) while no recordings could be made with other check stimuli, recordings that could be interpreted were obtained by flash stimulus.
The delay in the implicit time and decrease in amplitude of VER in patients with optic neuritis is now a universally accepted phenomenon . ,,13 In this study, nearly 20% of the VER recordings returned to normal with the improvement in visual acuity, a figure which closely agrees with that of Bynke et al  but is in contradiction to that of Halliday et a1  who had attributed the greater percentage of recovery to the lesser severity of cases in their series but this situation does not exist in our series where, all grades of severity of disease were seen. The lower cutoff limit of 2 standard deviation taken in our series as compared to the others along with lesser percentage of multiple sclerosis could explain some of these differences . 
Though we saw a definite improvement in value of both implicit time and amplitude on recovery, no proportionate correlation with visual acuity could be established in terms of lines of Snellen acuity.
VER may be an added parameter to complement the findings gained from the subjective tests like colour vision, field charting and pupillary reaction, each of which is important in its own right. It may be an indicator of previous attacks as seen by the persistent increased VER implicit time.
Prognosis in optic neuritis can thus be judged by such factors such as presence of painful eye movements, the initial visual acuity at the time of presentation, and recovery of colour vision. The VER helps to monitor a case at each step and gives knowledge of a past attack but does not really help in deciding the prognosis of a case of optic neuritis at the initial presentation.
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[Figure - 1], [Figure - 2]
[Table - 1], [Table - 2], [Table - 3], [Table - 4]