Multifocal Visual Evoked Potential In The Detection Of Glaucomatous Field Defects

Glaucoma has become one of the most common causes leading to irreversible blindness. Visual field defects were not only the results of glaucoma, but also one of the chief indicators in the diagnosis and treatment evaluation of glaucoma. Multifocal visual evoked potential (mfVEP) had a good sensitivity and specificity in the objective detection of visual field defects. Little cooperation was needed and no study curve existed when mfVEP was tested. Our study evaluated the effect of mfVEP on the detection of glaucomatous field defects.Our study had two parts. Part I evaluated the effect of electrode positions on mfVEP. 10 healthy individuals were tested with RETIscan multifocal VEP System 3.20 (ROLAND company, Germany) , each individual is tested with four electrode positions: the active and reference electrode were placed 3cm above and 4.5cm below the inion in Channel 1; 2cm above and below the inion in Channel 3; 4cm on both right and left side of the inion in Channel 2 and 2cm on both right and left side of the inion in Channel 4. The summed amplitudes of hemifield mfVEP were analyzed and compared according to different electrode positions. The results showed that the difference among summed amplitudes of the upper or lower hemifield mfVEP recorded with Channel 1 , Channel 2 , Channel 3 and Channel 4 were statistically significant; and the difference between Channel 1 and the other channels isstatistically significant too. The difference among summed amplitudes of the horizontal sites whose amplitudes are small when recorded with Channel 1 and summed amplitudes of the corresponding sites recorded with Channel 3 and Channel 4 were statistically significant; and the difference between Channel 2 and the other channels were statistically significant too. The results indicated that compared to Channel 2n Channel 3 and Channel 4, Channel 1 can make a better recording of mfVEP. As for some sites, especially those along horizontal line, horizontal electrodes could improve the amplitudes of mfVEP recorded with vertical electrodes, and Channel 4 could do better to improve the mfVEP recorded with Channel 1 than Channel 3. it was concluded that the combination of channel 1 and channel 2 was more preferable to record mfVEP.Part II evaluated the effect of mfVEP on the detection of glaucomatous field defects. 18 healthy individuals and 21 glaucoma patients were tested with RETIscan multifocal VEP System 3.20 and Octopus 101 automated perimetry G2 test program. Amplitudes was measured and interocular response asymmetry coefficient(RAC) was calculated for each site from all participants. The results indicated that 90% of the eyes suffered from glaucoma showed at least 3 adjacent points whose amplitude or RAC outside 2 standard deviations (SD) from healthy individual database. This indicated that mfVEP could be used to detect field defects of glaucoma.