Clinical studyLarge check size pattern reversal visual evoked potentials – Full and sectorial field stimulation in multiple sclerosis and controls
Introduction
Pattern Reversal Visual Evoked Potentials (PRVEPs) are useful in the investigation of multiple sclerosis (MS). While visual function often recovers following an acute episode of optic neuritis (ON), VEP abnormalities often persist indefinitely and can be used to identify past or subclinical demyelination. Traditionally, the conventional VEP uses a large full field alternating black and white checkerboard pattern. Previous studies have suggested smaller stimulus fields that specifically target the central visual field may be more effective in detecting abnormalities in ON [1], [2], [3], [4]. To help the confident identification of the P100, some studies have shown that the paramacular P135 component is enhanced when selectively stimulating the peripheral regions (known as the ‘hemisurround’ field) [5], [6].
Large rather than small check sizes may be preferable in clinical settings. While smaller check sizes are more sensitive for targeting the fovea[7] producing larger P100 amplitudes[8] than if large checks were used, this only holds true if patient has optimal refraction. Large checks do not produce latency shifts even when visual acuity is reduced to 6/60 [8], [9], [10]. In addition to this, age related changes are more pronounced when smaller check sizes are used [11], [12]. Altering the VEP through defocusing is more difficult with larger checks [13]. As such, we have chosen to compare the different stimulus patterns in the assessment of ON using a large check size (65′), with the view that larger checks are more resistant to latency and amplitude changes caused by aging, refractive errors and defocusing.
Central field and hemisurround stimulus in addition to full field and half field stimulus, using this large check size, were used in this set of patients with multiple sclerosis and past ON for the first time. The aim was to determine which stimulus field detects the most abnormalities and to determine the effects of sex, age and head size on latency and amplitude in our control group with this method.
Section snippets
Methods
We tested 35 normal healthy participants aged 21 to 65 years (19 females, mean age 41.8, and 16 males, mean age 40.3), with visual acuity (6/18 or better) and no history of ophthalmic disorders that could not be corrected with lenses. We analysed the differences in latency and amplitude with gender, occipitofrontal head circumference (OFC) and age. There were 21 patients (16 females, mean age 42.5, and 5 males, mean age 37.6) with MS as per the 2017 modified McDonald criteria [14], and either
Control data
PRVEP demonstrated shorter latencies and larger amplitudes in females than males (Table 1). Females were found to have P100 latencies that were on average 4.2 ms (P < 0.001) shorter than males, while amplitudes were on average 1.2 µV larger than males (P < 0.001).
No significant correlation was found between age and latency (rs = 0.038, P = 0.83) or age and amplitude (rs = -0.273, P = 0.113) in our controls (age range 21 to 65 years). The OFC was significantly different (P < 0.001) between the
Normal values
Our results are consistent with previous observations that females have shorter latencies than males [15], [16], [17]. It has been suggested that head size, rather than gender, explain these latency differences [17], [18]. Although males had significantly larger heads and longer P100 latencies than females in our control group, we did not find a statistically significant correlation between head size and P100 latency. This differs from Gregori et al. who found a weak but significant correlation
Source of funding
This work was supported by the National Health and Medical Research Council of Australia (ID 512316). No conflict(s) of interest.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors thank Anne-Sophie Veillard, biomedical statistician, of the NHRMC Clinical Trials Centre, University of Sydney, and the Royal North Shore MS service nurses, Saskia Lawler, Jane Kabanoff, and Lisa Gribbin.
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