Eyetracking-enhanced Visual Evoked Potential for Nystagmus, 2018-2023

Importance: Visual evoked potential (VEP) testing is an important part of a diagnostic workup and prognostic indicator of visual ability in patients with early onset nystagmus. However, VEP testing requires stable fixation, which is impossible for those with nystagmus. Fixation instability is believed to reduce VEP amplitude, and therefore VEP reliability is low in this important patient group.

Objective: To determine whether VEP amplitude can be increased by triggering acquisition only during slow periods of the nystagmus waveform.

Design: Cross-sectional study.

Setting: Data were collected at the Visual Electrodiagnostic Department at University Hospital Southampton, with clinical data from referring clinicians.

Participants: Thirteen individuals with nystagmus (10 early onset nystagmus and three late onset nystagmus).

Exposure: VEP obtained under continuous (standard) acquisition, or triggered during periods of low eye velocity, as detected by an eye tracker. Trigger velocity threshold was determined per-participant.

Main outcome and measure: VEP amplitude.

Results: VEP amplitude is significantly increased when triggered during low eye velocity in patients with early onset nystagmus (95% CI 1.42-6.83 µV, t(15) = 3.25, p = .0053), but not in patients with late onset nystagmus (95% CI -3.92-11.59 µV, t(5) = 1.27, p = .26).

Conclusions and relevance: This study provides proof-of-concept that VEP amplitude (and therefore prognostic reliability) can be increased in patients with early onset nystagmus by triggering acquisition during periods of lower eye velocity.

重要性：视觉诱发电位（Visual Evoked Potential, VEP）检测是早发性眼球震颤患者诊断评估流程中的关键环节，同时也是评估该类患者视觉能力的预后指标。然而，VEP检测要求患者保持稳定注视，而眼球震颤患者无法实现这一要求。现有研究认为，注视不稳定会降低VEP振幅，因此在这一重要患者群体中，VEP检测的可靠性较低。
研究目的：旨在明确仅在眼球震颤波形的慢速时段触发数据采集，是否能够提升VEP振幅。
研究设计：横断面研究。
研究地点：数据采集于南安普敦大学附属医院视觉电生理科，临床数据由转诊医师提供。
研究对象：共纳入13名眼球震颤患者，其中10名为早发性眼球震颤患者，3名为迟发性眼球震颤患者。
干预措施：分别采用两种方式获取VEP：一是连续（标准）采集模式，二是通过眼动仪检测到眼速较低时段时触发采集；每名受试者的触发眼速阈值均个体化设定。
主要结局与指标：VEP振幅。
研究结果：早发性眼球震颤患者在眼速较低时段触发采集时，VEP振幅显著升高（95% CI 1.42-6.83 µV, t(15) = 3.25, p = .0053）；而迟发性眼球震颤患者未观察到该现象（95% CI -3.92-11.59 µV, t(5) = 1.27, p = .26）。
结论与意义：本研究提供了概念验证结果，证明通过在眼速较低的时段触发采集，可提升早发性眼球震颤患者的VEP振幅（进而改善预后评估的可靠性）。