Iyer Kartik K, Bradley Andrew P, Wilson Stephen J
School of Information Technology and Electrical Engineering, University of Queensland, Queensland, Australia,
Doc Ophthalmol. 2013 Feb;126(1):21-8. doi: 10.1007/s10633-012-9355-9. Epub 2012 Oct 26.
The estimation of visual acuity (VA) via visual evoked potentials (VEP) is a valuable measure for all preverbal and non-verbal subjects whether adults or children. The aim of this study is to introduce a novel technique of VEP acquisition based on estimates of signal-to-noise ratio (SNR) and comparison to a predefined detection threshold. We aim to demonstrate the reduction in total study time without compromising the accuracy of the VEP-determined acuity estimate.
The VEP-determined acuity of twelve normal subjects was assessed via a spatial frequency (SF) sweep. A pattern reversal checkerboard stimulus utilised SFs ranging from 0.1 to 28 cycles per degree (cpd). Using linear extrapolation and Bland-Altman analysis, VEP-acquired acuity was compared to a conventional Snellen Acuity measurement. An SNR test, Fsp, assessed signal quality to determine the minimum amount of sweep data required for VEP-based VA estimation.
VEP acuity estimates correlated strongly (r2=0.91, SD=0.06), leading to a VA limit via extrapolation. Bland-Altman analysis revealed agreement between tests is statistically valid (95% CI -0.11 to 0.42 logMAR). The Fsp statistic indicated SFs 1.3-3.6 cpd yielded Fsp>3.1 within 15 s of acquisition with frequencies>3.6 cpd being sub-threshold. The Kruskal-Wallis statistic compared final Fsp values for SFs as groups, where F=208.82 ranking each frequency, with frequencies>7.2 cpd ranking lowest.
The Fsp as an SNR measurement shows that rapid, quality-driven clinical tests for VEP-based acuity estimates can be conducted without compromising accuracy.
通过视觉诱发电位（VEP）评估视力（VA）对于所有无法言语或不言语的受试者（无论成人还是儿童）都是一种有价值的测量方法。本研究的目的是引入一种基于信噪比（SNR）估计的VEP采集新技术，并与预定义的检测阈值进行比较。我们旨在证明在不影响VEP确定的视力估计准确性的情况下，减少总研究时间。
通过空间频率（SF）扫描评估12名正常受试者的VEP确定的视力。使用模式反转棋盘格刺激，其空间频率范围为每度0.1至28周/度（cpd）。使用线性外推法和布兰德-奥特曼分析，将VEP获得的视力与传统的斯内伦视力测量进行比较。SNR测试Fsp评估信号质量，以确定基于VEP的视力估计所需的最小扫描数据量。
VEP视力估计值之间具有很强的相关性（r2 = 0.91，标准差 = 0.06），通过外推得出VA极限。布兰德-奥特曼分析表明，测试之间的一致性在统计学上是有效的（95%置信区间 -0.11至0.42 logMAR）。Fsp统计表明，空间频率为1.3 - 3.6 cpd时，在采集15秒内Fsp>3.1，而频率>3.6 cpd低于阈值。Kruskal-Wallis统计将各空间频率的最终Fsp值作为组进行比较，其中F = 208.82对每个频率进行排名，频率>7.2 cpd排名最低。
作为SNR测量的Fsp表明，可以在不影响准确性的情况下进行基于VEP的视力估计的快速、质量驱动的临床试验。
