Evaluation of the effect of myopia on visual evoked potential in medical students

ABSTRACT

Background: Visual evoked potentials (VEPs) are electrical potential differences recorded from the occipital lobe in response to different visual stimulus. In myopic individuals, there is blurring of the stimuli, causing defocusing which tends to affect the VEP parameters. Aim and Objective: The study was designed and done to evaluate the effect of various degrees of myopia on VEP in medical students of age 18–24 years. Materials and Methods: A total of 120 subjects were included in this study, consist of 60 individuals without having any refractive disorders and 60 individuals having various degree of myopia, that is, 22 subjects with mild myopia of <?3D, 26 subjects with moderate myopia of ?3 to ?6D, and 12 subjects with severe myopia of > ?6D. The study was approved by Ethical and Research Committee, Govt. Medical College, Patiala. Results: In the present study, mean values for P100 latency were significantly high in myopic group as than in control group. Furthermore, mean values for N75 latency were significantly high in the myopic group as compared to the control group and mean values for N145 latency were significantly high in the myopic group as compared to the control group for both the right and left eyes. Mean values for amplitude (N75-P100) was significantly lower for the myopic group as compared to the control group for both the left and right eyes. There is prolongation of latencies in myopic individuals as compared to the control and latencies increase with the increase in degree of myopia. Furthermore, there is decrease in the amplitude in myopic individuals and it decreases with the increase in degree of myopia. Conclusion: The mean values for latencies were found to be comparable and the mean values of latencies were found to be increasing with increase of degree of myopia. Probably, the reason behind this result may be the optical blurring of the stimulus which lead to defocusing, therefore causes the prolongation of latency. The mean values for amplitude were found to be comparable and the mean values of amplitude were found to be decreasing with increase of degree of myopia. Probably, the reason for our finding is that in a pattern reversal VEP, the amplitude relies on the visual system’s ability to determine the pattern and on the degree of retinal image focus.