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S. Mizunoya, T. Sugawara, J. Uehara, K. Ogata, S. Yamamoto; The Ganglion Cell Component of the I-Wave in the Photopic ERG. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4182.
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© ARVO (1962-2015); The Authors (2016-present)
The i-wave component (Nagata, 1963) of the photopic electroretinogram (ERG) was reportedly derived from near ganglion cell (GC) layer in human (Lachapelle, et al, 1990 and 1996). To investigate GC component of the i-wave, photopic ERGs were recorded in patients with unilateral chronic optic nerve disease in this study.
After adequate informed consent was obtained, five patients with unilateral optic disc atrophy were examined. Patients’ age ranged 27- 63 (mean: 42.3) years old. After 10 min light adaptation, photopic ERGs were recorded using LED contact lens electrodes and LE2000 system (TOMEY). The photopic b-wave, i-wave, photopic negative response (PhNR) were analyzed and compared with those from five age-similar normal controls.
Results were showed below. Numbers indicate mean values. The AE and FE mean affected and fellow eye, respectively. The RE and LE mean right and left control eye, respectively. The PhNR (µV) were 20.4*(AE), 42.2 *(FE), 43.7(RE), 45.0(LE). The i-wave (ms) were 49.0(AE), 48.2(FE), 47.4(RE), 47.5(LE). The i-wave (µV) were 30.5(AE), 35.8(FE), 45.9(RE), 47.0(LE). The b-wave (µV) were 160.5(AE), 170.2(FE), 205.2(RE), 210.1(LE). The i/b ratio were 0.19(AE), 0.21(FE), 0.22(RE), 0.22(LE). The i/b(AE)/ i/b(FE) were 0.90* (AE/FE), 1.00* (RE/LE). Statistical analyses were performed using paired-t test (*p<0.05).
There was no statistical difference in both i-wave implicit time and i-wave amplitude, thus, i-wave may not be a good indicator for the GC function. The AE/FE ratio of the i/b ratio was related to GC component because of their variation depending on subject, but the PhNR was better indicator for GC function in the LE 2000. Therefore, the origin of the i-wave should be not only near GC but also surrounding of the GC.
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