Pattern electroretinogram (PERG) allows assessment of ganglion cell function and may therefore be used to assess anterior visual pathway dysfunction. This prospective non-randomised study assessed PERG before and after surgical removal of tumours in and around the sellar region compressing the anterior visual pathways in order to assess its utility as a prognostic tool. Best corrected visual acuity (BCVA), Humphrey visual field (VF) (30-2) and PERG were recorded one week preoperatively, one week and six weeks postoperatively. During PERG, the first negative wave (N1), the first prominent positive wave (P1/P50) and the second large negative wave (N2/N95) were recorded to calculate the N2/P1 ratio. ≥1.1 was taken to be normal and <1.1 was abnormal. Twenty patients (40 eyes) were included. Thirty-one eyes (77.5%) had a normal N2/P1 ratio preoperatively. This increased to 34 eyes (85%) in the early postoperative period and 35 eyes (87.5%) in the late postoperative period. There was no association between PERG and BCVA in the pre and postoperative periods (P=0.369). Of eyes with normal N2/P1 ratio, 47.1% showed an improvement in BCVA, compared to 50% eyes with abnormal N2/P1 ratio. There was also no significant association between PERG and VF pre and postoperatively (P=0.093). Of eyes with a normal N2/P1 ratio, 35.4% showed an improvement in VF postoperatively compared to 22.2% eyes with abnormal N2/P1 ratio. Of eyes with a normal N2/P1, 45.2% showed no change in VF postoperatively compared to 66% with an abnormal ratio. In conclusion, PERG is unlikely to be a useful prognosticator in the preoperative assessment of chiasmatic tumours, as an abnormal N2/P1 ratio is not associated with lesser or no clinical improvement post surgery when compared with a normal N2/P1 ratio.
PERG as a visual prognosticator in chiasmatic tumours
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