The effects of glaucoma on the latency of the multifocal visual evoked potential

Abstract

Aims: To determine the effect of glaucomatous damage on the latency of the multifocal visual evoked potential (mfVEP). Methods: Monocular mfVEPs were recorded from a glaucoma group (n = 50) defined by a glaucomatous disc and an abnormal visual field and a control group (n = 47). 25 patients were characterised as normal tension glaucoma (NTG) and 25 as high tension glaucoma (HTG). Monocular and interocular latency analyses of the more affected eye were obtained using custom software. Results: On interocular analysis, both the HTG and NTG groups showed a statistically significant increase in mean mfVEP latency with average relative latencies and percentage of points with significant delays of 1.7 ms and 10.3% (HTG) and 1.3 ms and 8.2% (NTG) compared to 20.3 ms and 2.7% (controls). On monocular analysis, only the HTG group showed a significant increase in latency with measures of 5.7 ms and 14.6% (HTG) compared to 3.2 ms and 10.6% (NTG) and 2.1 ms and 9.6% (controls). Using the 95th percentile of a normative group as the cut off, the sensitivity ranged from 20% to 38% and the specificity from 87% to 100% with the interocular analysis providing the best discrimination, Conclusion: Although up to 40% of patients showed delays in the mfVEP latency, these delays were modest, on average a few milliseconds. These results differ markedly from those of a recent conventional VEP study, which reported 100% sensitivity, 100% specificity, and an average delay that exceeded 25 ms. G laucoma, a widely prevalent eye disease, is characterised by an optic neuropathy, often associated with elevated intraocular pressure, leading to characteristic visual field defects and optic nerve head damage. It is well established that damage to the ganglion cells and/or their axons produce these visual field defects. What is less clear is the extent to which the ganglion cells undergo a rapid apoptotic death as opposed to lingering in an abnormal state. If the latter holds, then it raises the possibility of neuroprotection of unhealthy retinal ganglion cells. A possible indicator of the health of the retinal ganglion cells is the latency of their response.There have been a number of studies with conventional visual evoked potentials (cVEP) showing large latency delays, of the order of 20 ms, in glaucoma patients.1-5 A recent study 5 reported that all their patients with open angle glaucoma had abnormal cVEP latencies with an average latency that was 27.8 ms longer than the control group. Further, the cVEP latency has been used as a marker of reversible ganglion cell damage in trials of neuroprotective agents for the treatment of glaucoma. 6 The implication is that latency can be used as a measure of early glaucomatous damage before retinal ganglion cell death.A potential problem with the cVEP is that it represents the weighted sum of many local responses. Thus, the technique may obscure delays in local responses. These delays in latency should be seen more easily with the multifocal VEP (mfVEP). With the mfVEP technique, multiple responses, corr...

Evaluation of multifocal visual evoked potentials in patients with Graves’ orbitopathy and subclinical optic nerve involvement

“…Although latencies are known to be increased in hypothyroidism [29][30][31], our patients were euthyroid at the time of this study. The latency delays seen in these patients were in the same range as those described in patients with compressive optic neuropathies and much longer than those seen in glaucomatous or ischemic optic neuropathies [32,33].…”

Delayed saccadic eye movements in glaucoma

“…38,39 It is interesting to note that delayed saccades are found in patients with mild visual field loss, as well as in advanced cases. It is not yet known whether the increased latency of nerve conduction in the retino-geniculate pathway 40,41 and/or the decreased amplitude of retinal ganglion cell response 42 reported in some glaucoma patients contribute to delayed saccades in glaucoma patients. Further studies are needed to determine whether the retinal ganglion cells conveying visual information to the saccade-generation network are affected in glaucoma.…”

Statistical test of VEP waveform equality

“…3,4,5,6,7,8,9). First, we examined whether phase-scrambling can be performed when the VEP waveforms are almost free of any noise versus when the waveforms are very noisy.…”

“…While such method has proven useful in the clinic, the method is feasible only when a signal can be unambiguously identified [2,3], motivating some investigators to explore alternative methods of analysis [4][5][6]. The present study examines a new method based on a statistical test of waveform equality.…”