|Year : 1982 | Volume
| Issue : 4 | Page : 305-306
Visual evoked response in optic atrophy
BPS Malhotra, DK Gahlot
Dr. Rajendra Prasad Centre for Ophthalmic Sciences, New Delhi-110029, India
Dr. Rajendra Prasad Centre for Ophthalmic Sciences New Delhi-29
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Malhotra B, Gahlot D K. Visual evoked response in optic atrophy. Indian J Ophthalmol 1982;30:305-6
When the light falls on the retina, a volly of nerve impulses is set up and is transmitted via visual pathways to occipital cortex. These potentials can be measured by electrodes, placed over the region of the cortex and are called Visual Evoked Responses (VER). The recording of VER has recently been made possible by the development of computer averaging techniques. The VER evoked by fla
shes of light is variable both as regards latency and waveforms. However, in VER evoked by check pattern the latency of the maj or positive component is more consistent and reliable. No report is available in literature about VER changes in optic atrophy. This paper compares the VER changes in normals with those of frank optic atrophy and those having loss of vision without optic disc changes.
| Materials and methods|| |
40 patients of optic atrophy and traumatic loss of vision were taken from the NeuroOphthalmology Clinic of the Dr. Rajendra Prasad Centre for Ophthalmic Sciences. They were divided into three groups
Twenty patients with primary optic atrophy due to various causes like pituitary tumour. ischaemic neuropathy, netrobulbar neuritis and other indeterminate causes. Here one or both eves were involved with visual acuity ranging from no perception of light to 6/60.
Ten patients, eight being of bilateral postpapilloedemic optic atrophy and two of unilateral postneuritic optic atrophy. Here the visual acuity was variable ranging from no perception of light to accurate perception and projection except one who had counting fingers at 2 metres.
Ten patients with loss of vision following direct or indirect trauma to eye during road side accidents. In these cases only one eye was involved and fundus was normal. The visual acuity was reduced to no perception of light except one who had 6/24 with accurate projection.
The visual evoked potentials were recorded from both the eyes separately using full optical correction with identical parameters. The patients were made to sit at a distance of one metre from the visual stimulator in a semi-dark room. The electrodes were attached to scalp 12 cm. above the nasion and 5 cm. above the inion after thoroughly cleaning the area with ether. The indifferent electrode was fixed over the ear lobule. 100 repetitions of reversal check pattern 3202 mm at the rate of 1.99 cycles/ sec. on CA-1000 clinical signal averager system of Nicolet Instrument Corporation were given and the waveform were plotted by the x-y plotter
| Observations|| |
Patients with primary optic atrophy who had either no perception or only perception of light the VER showed no pattern. The patients who had visual acuity ranging from finger counting to 6/18 with optic atrophy the VER was either absent or subnormal i.e. the latency and amplitude were markedly decreased
In secondary optic atrophy irrespective of the cause and vision the VER was totally absent
In this group patients without disc changes showed absent VER in the affected eye irrespective of visual acuity
| Discussion|| |
Visual evoked response is a minute change in the amplitude of the background potentials of the brain. This change is initiated by the light stimulation of the retina and corresponds with the approach of stimulatory impulse to the occipital cortex. From there after adequate amplification and averaging it is picked up and displayed. In recent years the VER is being increasingly used in evaluating a number of ophthalmic diseases particularly those affecting the retina and optic nerve. The VER, being related to the conduction of visual impulses through visual pathways, is affected either in its amplitude or latency or both. Hence it is considered very valuable in' the objective assessment of macular and optic nerve functions in patients with visual symptomatology but without any obvious fundus changes.
In the case of optic atrophy both primary and secondary nerve fibres being atrophic and dead, do not conduct visual impulses. Hence VER is absent. In cases of some residual vision and partial atrophy since some impulses are conducted, VER is present but there is either delay in conduction hence increase in latency, or decrease in amplitude.
In cases of trauma the vision may be totally lost either due to complete transaction of the optic nerve or haemorrhage in the optic nerve sheath. If the vision is only partially lost it is most likely due to incomplete laceration of the nerve fibres. These events occurring behind the globe are neither visible ophthalmoscopically nor radiologically. In the former case VER is absent and in the latter it is subnormal i.e. latency is increased and amplitude decreased. If the VER is absent in the latter case also it indicates a bad prognosis. Thus,
it is observed that the VER is grossly affected in all groups irrespective of their aetiology. Hence VER is of definite value regarding the prognosis of vision.
| Summary|| |
40 patients of optic atrophy and traumatic loss of vision were studied. It was found that the VER was either absent or subnormal in all cases suggesting that if the VER is grossly affected chances of visual recovery are remote.