Effects of acutely lowering intraocular pressure on the results of multifocal visual evoked potential testing

Abstract

There have been many reports in the literature on the apparent reversal of optic nerve cupping in patients with glaucoma after lowering intraocular pressure (IOP) on clinical examination, as well as improvement in visual field testing, and increased nerve fibre layer thickness on optical coherence tomography. No studies to date have looked at improvement of multifocal visually evoked potentials (mfVEP) after lowering IOP. This was a prospective study of twenty consecutive patients with elevated IOP seen in the glaucoma department of Wills Eye Institute. Patients who met the inclusion criteria for this study had a complete eye examination including IOP measurement and underwent testing with mfVEP, Heidelberg Retinal Tomograph (HRT) and static achromatic automated perimetry with SITA-Standard 24-2 program Humphrey visual field (HVF) studies at baseline and 2 h post-IOP reduction. A minimum of 30% IOP reduction was required. IOP changes were then compared with various parameters of mfVEP, HRT and HVF using Spearman rank correlation coefficients. The Spearman rank correlation values between change in IOP versus various parameters were calculated: Accumap severity index (ASI), 0.37 (p = 0.14); Accumap superior hemifield, 0.049 (p = 0.85); Accumap inferior hemifield, 0.030 (p = 0.91); HVF mean deviation, 0.081 (p = 0.76); HRT rim area, 0.17 (p = 0.51); HRT cup area, -0.006 (p = 0.98). Weak positive but insignificant correlations were seen for all parameters except cup area. This pilot study failed to confirm statistically significant correlations between IOP reduction and changes in Accumap, HVF and HRT measures, although positive correlations were seen for most measures.