Author(s): Kothari Ruchi, Singh Ramji, Singh Smita, Bokariya Pradeep
Glaucoma is a widely prevalent eye disease characterized by an optic neuropathy, often associated with elevated intraocular pressure, leading to characteristic visual field defects and optic nerve head damage. Pattern- induced visual evoked potentials (VEPs) have been shown to be sensitive to glaucomatous neuropathy. The elevation of intraocular tension is believed to cause pressure on the retinal nerve fibers bundles as they course into the optic nerve and is associated with the loss of visual function; which alters the VEP waveforms. The present study was conducted to compare the pattern reversal visual evoked potentials (PREVPs) in patients with primary open angle glaucoma and in healthy controls to assess the utility of VEP in detecting early cases of primary open angle glaucoma. 90 primary open angle glaucoma (POAG patients) and 120 control subjects underwent VEP investigation in the Neurophysiology Unit of Dept. of Physiology, Mahatma Gandhi Institute of Medical Sciences, Sevagram on Recorders and Medicare Systems RMS Electromyograph (EMG) Evoked Potential (EP) Mark MKII. The latency and amplitude of first positive wave P100, and the latencies of the negative waves N70and N155 respectively in PR-VEP were recorded. Visual fields of all POAG patients were assessed by Humphrey field analyzer program 30-2 full threshold. The differences of PRVEP parameters among POAG and control groups were compared and it was found that P100 latency was prolonged in 172 eyes of 86 (88.89%) patients among the POAG group. P100-N70 amplitude was reduced in 160 eyes of 80 (88.89%) patients among the POAG group. None of the patients in our study failed to record a measurable response in either eye. The Mean Deviation (MD) values in the POAG patients were negatively correlated with the latency time of P100. No significant correlation was found between PSD and latency time or between PSD and amplitude of P100 among the POAG patients. Primary open angle glaucoma has been found to affect the PRVEP by causing both the reductions in P100 amplitude and increments in P100 latency when compared with that of the control group. Visual field index MD was found to be negatively correlated with the P100 latency. Our study advocates the use of PRVEP as an objective electrophysiological tool for monitoring patients with the progression of optic nerve pathology in POAG, because increase in latency times are significantly associated with progression of optic nerve damage