Investigating the effects of glaucomatous (POAG) damage on the mVEP parameters

Introduction: Glaucoma is considered as a major cause of irreversible vision loss, worldwide. Glaucoma includes a diverse ophthalmopathies characterized by attenuating the neural and connective tissue segments and eventually progression of specific patterns of visual dysfunction. Currently, perimetry is known as the most accurate diagnostic method in glaucoma and its follow up. For all patients with visual field defects, automated perimeters, such as the Humphrey Field Analyzer (HFA), enable rapid screening. This technique suffers from some disadvantages. Electrodiagnosis could be considered as an optional method in ophthalmology. Two important aspects of this method are its functionality and objectivity. The main purpose of this study is to investigate the effects of glaucomatous damage on the mfVEP parameters of patients suffering from primary open angle glaucoma (POAG).   Materials and Methods: The study was conducted at the ophthalmology clinic of Imam Khomeini hospital of Ahvaz. 15 healthy subjects and 15 patients with POAG. In addition to routine ophthalmological examinations including visual acuity, anterior segment examination, posterior segment examination, intra-ocular pressure, mfVEP with electrophysiological system, Reti Port/Scan 21 and visual field test with automated Humphrey ZEISS HFA II 750i Perimeter were also performed. All patients were categorized as unilateral POAG. The  MD  and PSD in more involved eyes in POAG patients were -6.72 (SD= ± -5.61) and 5.6 (SD= ± 4.95), respectively. To obtain an mfVEP, the low- and high- frequency cut off of recording was amplified at 1 and 100 Hz. The sample rate was set at about 1020 times per second.   Results: In this study, visual field assessing using mfVEP was applied to diagnose glaucomatous damage and also to determine the correlation of the ΔmfVEP parameters with the Δglobal indices (MD and PSD) between the two eyes of each patient by three following approaches. In the first and the second methods, intersubject and intrasubject comparisions between Δglobal indices of the HFA in the interpolated visual fields and ΔmfVEP parameters were done and no correlations were found. In the third method, the correlation between the number of points in each sector of mfVEP with the Δamplitude and the Δlatency in each patient (> mean ± 2SD) was determined. Moreover, the correlation of those points with the Δglobal indices of patients was clarified. there was a strong correlation between the ∆MDs and the number of abnormal points with the ∆amplitudes more than 256 nV, in POAG subjects (n = 15, r = 0.802, p <0.05). Conclusion: Comparing the monocular mfVEP responses from both eyes is an appropriate method to detect unilateral damage. Achievement of more development and making the mfVEP test more functional, can be a solution for early diagnosis in most of the eye diseases.