University Journal of Pre and Para Clinical Sciences

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1 ISSN Volume 3 Issue Pattern Reversal Visual Evoked Potential in Glaucoma SAMUNDEESWARI Department of Physiology, STANLEY MEDICAL COLLEGE AND HOSPITAL Abstract : Glaucoma,a disorder of the eye, is recognised as one of the leading cause of blindness among adult population.central nervous system particularly the visual pathway gets involved even before the onset of symptoms. Visual evoked potential can be employed as a tool in these group of patients to find out the involvement of nervous pathways at the subclinical stage in a simple and non invasive way. The aim of the study is to evaluate visual evoked potentials in glaucoma patients and to compare it with age and gender matched healthy controls. To assess the association between waveforms of VEP and cup disc ratio in individuals affected with glaucoma.30 glaucoma subjects and 30 healthy controls are enrolled for the present study. VEP recording is done using white and black checkerboard stimulation pattern. N75, P100 and N145 latencies and P100-N75 amplitude are recorded.the present study reveals the latencies of N75 and P100 are increased in glaucoma patients that are statistically significant as compared to the control group. There is also a significant correlation between the latency of VEP parameters and cup disc ratio.alterations in optic nerve pathway can be detected at the preclinical stage using Pattern reversal visual evoked potential in glaucoma patients. Visual Evoked Potential can be applied as a non -invasive tool to evaluate and to monitor the visual pathway to prevent or delay the progression of blindness in glaucoma patients at the earlier stages. Keyword :Glaucoma, pattern reversal visual evoked potential, cup disc ratio, P100 waveform INTRODUCTION Glaucoma is the second common cause of irreversible blindness affecting adult population, next to cataract. 1, 2 The estimated prevalence of population based studies in India states that glaucoma affects 11.9 million people. 3-5 Early detection of glaucoma will help clinicians to herald the progression of disease and to retain the vision. 6 The techniques employed to detect the damages caused by glaucoma are intraocular pressure measurement, optic disc evaluation and

2 visual field testing. 7 Alternative ways of detecting and monitoring glaucoma are being sought by clinicians because currently used investigations are costly and time consuming. 8 Visual evoked potential (VEP) is a sensitive method to find out abnormalities in the optic pathway distal to retina Visual evoked potential is an evoked electrophysiological potential that can be extracted, using signal averaging, from the electroencephalographic activity recorded at the scalp. The VEP can provide important diagnostic information regarding the functional integrity of the visual system. Pattern reversal is the preferred technique for most clinical purposes. The pattern reversal VEP is the preferred stimulus because of less variability in the waveform and timing than the VEPs elicited by other stimuli. AIM OF THE STUDY This study was done to analyze the Visual Evoked Potentials in glaucoma patients and to study the following parameters in glaucoma patients namely: N75, P100, N145, P100 N75 and to compare the above mentioned parameters to that of controls. MATERIALS AND METHODS The present study was conducted at Neurophysiology laboratory in the Department of Physiology,Stanley Medical College, Chennai. Ethical approval from Ethical Committee of our institution wasobtained for the study. Written and informed consent was obtained from all participants. It was a case control study with two groups of 30 patients each: one group as study and another one as control. The study group included glaucoma patients of age group years. Patients with optic neuritis, opacities of cornea and lens, macular or visual pathway lesions, diabetes mellitus, Parkinson disease and multiple sclerosis were excluded. Three surface disc electrodes were used: reference, ground, active under high filter cut hg. Electrical impedance was kept below kilo ohms. Black and white checkerboard was used. Distance between the subject and screen was 100 cms. Subject was instructed to fix gaze at the center of the screen. Subject was asked to sit comfortably on a chair with their foot wear. Each eye was tested separately. Other eye was kept covered with an opaque eye shield which prevents entry of light into that eye. The skin was degreased at the electrode placement with spirit.the gaze was fixed at the center of the screen, lights were switched off. Visual stimulus was delivered by photo stimulator at a frequency of 10 flashes / sec. Response obtained was displayed on TV monitor and peak latency and peak-peak amplitude of the waves were measured. VEP consists of series of waveforms of opposite polarity, negative form denoted as N and positive waveform denoted as P. The patients were explained about the test to ensure full co-operation and were advised to avoid hairspray/oil after their last hair wash. The usual glasses, if any, were put on during the test. The results of ophthalmological examination such as visual acuity, pupillary diameter and field chart were reviewed before starting the test. Any miotic or mydriatic drugs were avoided 12 hours before the test. Recordings were done in the sitting position between 10 A.M.to1 P.M. after light breakfast. The techniques of measurements, duration and instruments were maintained throughout the study. Participants were made to relax and be comfortable prior to tests. Detailed clinical history about Glaucoma was collected. Height and weight were measured for all the subjects. VEP recordings were done using RMS ENMG EP MARK II Machine in a standard manner. The guidelines given by International Federation of Clinical Neurophysiology Committee were followed in this study

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4 RESULTS Statistical Package for Social Sciences (SPSS) software 16 version was used for statistical analysis. The student independent t test was used to compare the study group and the control g r o u p. Pearson s correlation test was used to correlate VEP parameters and cup-disc ratio. TABLE 1: There is no statistical difference between the study group and the control g r o u p w i t h regards to age (p > 0.05). TABLE 2: There is highly significant increase in intraocular pressure in right eye and left eye in the study group when compared to the control g r o u p ( p < ). TABLE 3: The latency of N75 in the right eye is highly significantly increased in the s t u d y g r o u p (p<0.01).there is highly significant increase in P100 latency of the right eye in t h e s t u d y g r o u p compared to the control group (p <0.01). TABLE 4: N75 latency in the left eye is highly significantly increased in the study g r o u p ( p < ). There is highly significant increase in P100 latency of the left eye in the study group compared t o t h e control group (p <0.01). TABLE 5: Using Person s correlation coefficient, there is no significant correlation b e t w e e n V E P parameters and cup disc ratio in the study group in the right eye (p >0.05). TABLE 6: There is positive correlation between P100, N145 and cup disc ratio in the left eye in the study group that is statistically significant (p<0.05). DISCUSSION. Our study shows that there are significant changes in central nerve conduction in glaucoma subjects. The latency of N75 is prolonged in the study group when matched with the control group. 13 Stimulation of striate and peristriate cortex leads to generation of P100 waveform. P100 waveform varies little between the subjects and with repeated measurements. The study group show prolongation of P100 latency as compared to the control group which is in agreement with study conducted by Parisi et al, 14 Tong et al, 15 Rouland et al, 16 Cappin et al. 17 There is a significant positive correlation between VEP latency and optic disc cupping as shown in study done by Towle et al. 18 It has been shown that

5 pattern reversal visual evoked potential is useful in detecting optic nerve lesions caused by demyelination, ischemia and anterior visual pathway compression. 19 Vascular etiology such as decreased blood flow to the optic nerve leading to death of axons results in changes in waveform that is shown by VEP study. 20 CONCLUSION Thus the present study reveals deficit in optic pathway conduction. Thereby, VEP can be used as a noninvasive tool to detect optic nerve damage at the earlier stage in Glaucoma subjects to prevent or delay the progression to irreversible stage. Limitations: Longer follow up and larger sample size are to be included. REFERENCES 1 Vijaya L, George R, Arvind H, et al. Prevalence and causes of blindness in the rural population of the Chennai Glaucoma Study.Br J Ophthalmol2006;90 (4): Thulasiraj RD, Nirmalan PK, Ramakrishnan R, et al.blindness and vision impairment in a rural south Indian population: the Aravind Comprehensive Eye Survey. Ophthalmology 2003;110 (8): Jacob A, Thomas R, Koshi SP et al. Prevalence of primary glaucoma in an urban south Indian population.indian J Opthalmol 1998;46(2):81-6. Ophthalmology 2003;110(8): Graham SL, Drance SM, Chauhan BC, SwindelaNV, Hnik P, Milkelberg FS, et al. Comparison ofpsychophysical and electrophysiological testing in early glaucoma. Invest Ophthalmol Vis Sci 1996;37(13): Greaney MJ, Hoffmann DC, Garway Heath DF,Nakla M, Coleman AL, Caprioli J. Comparison ofoptic nerve imaging methods to distinguish normal eyes from those with glaucoma. Invest Ophthalmol Vis Sci 2002;43: Bjerre A, Grigg JR, Parry NRA, Henson DB. Test retest variability of multifocal visual evokedpotential and SITA standard perimetry in glaucoma.invest Ophthalmol Vis Sci 2004;45(11): Nainiwal S, Garg SP, Tewari HR. ERG, EOG and VER. Delhi J Ophthalmol 2004;10(1): Kolker AE, Hetherington J, editors. Primary openangle glaucoma. In: Becker Shaffer s diagnosis andtherapy of glaucoma. 5th ed. St. Louis; Toronto: The CV Mosby Company Publication; p Arvind H, Paul PG, Raju P, Baskaran M, George R, Balu S, et al. Methods and design of the Chennai Glaucoma Study. Ophthalmic Epidemiol 2003;10(5): Ramakrishnan R, Nirmalan PK, Krishnadas R, Thulasiraj RD, Tielsch JM, Katz J, et al. Glaucoma in a rural population of southern India: the Aravind Comprehensive Eye Survey. 11 Greenstein VC, Thienprasiddhi P, Ritch R,Liebmann JM, Hood DC.A method for comparing electrophysiological, psychophysical and structural measures of glaucomatous damage. Arch Ophthalmol 2004;122:

6 1 2 Celesia GG, Bodis WI, Chatrian GE, Harding GFA,Sokol S, Spekreijse H. Recommended standards for electroretinogram and visual evoked potentials.report of an IFCN committee. Electroencephalogr Clin Neurophysiol 1993;87: Bechetoille A. Vascular risk factors in glaucoma. Curr opin Ophthalmol 1996;7(2): OBSERVATIONS 13 Snegir MA. Modifications of Visual Evoked Potentials in Patients with Glaucoma. Neurophysiology, vol 34, No.1, Parisi V. Impaired visual function in glaucoma. Clin Neurophysiol Feb;112(2): Tong Y, Wang P, Xia Z, Xia X, Xu X. Color pattern reversal visual evoked potentials in primary open angle and angle closure glaucoma. Zhong Nan Da Xue Xue Bao Yi Xue Ban Aug;34 (8): Rouland JF, Hache JC. Visual evoked potentials in glaucoma and ocular hypertension. J Fr Ophtalmol. 1987;10(3): Cappin JM and Nissim S: Visual evoked responses in the assessment of field defects in glaucoma. Arch Ophthalmol 93:9, Towle VL, Anne Moskowirz, Samuel Sokol, Bernard Schwartz.The Visual Evoked Potential in Glaucoma and Ocular Hypertension: Effects of Check Size, Field Size, and Stimulation Rate. Invest Ophthalmol Vis Sci 24: , Halliday AM, Halliday E, Kriss A, McDonald WI, and Mushin J: The pattern -evoked potential in compression of the anterior visual pathways. Brain 99:357, 1976.