Purpose

VEP-based estimation of visual acuity may be used in cases of suspected malingering to objectify subjective complaints. In such an application, a lack of cooperation needs to be expected. The same may apply to young children with suspected functional impairments. In the present study, we assessed how inaccurate fixation affects the acuity estimates obtained with a VEP technique.

Methods

VEP-based acuity estimates were obtained by stimulating with a series of different check sizes using a ‘stepwise sweep’ protocol. Sixteen participants were tested with normal and degraded vision under five different fixation conditions (central fixation and eccentric fixation at top, bottom, right, and left edge of the stimulus area).

Results

The majority of individual acuity estimates with eccentric fixation differed by less than 0.1 logMAR from central fixation, and almost all estimates differed by less than 0.3 logMAR. Median estimates with eccentric fixation differed only slightly (up to 0.08 logMAR) and, except for top fixation with normal vision, non-significantly. However, data quality was lower with eccentric fixation, which increased the probability that no acuity estimate could be derived from the recording.

Conclusion

VEP-based acuity estimates are relatively insensitive to eccentric fixation. Unnoticed deviations from central fixation in routine applications will probably be smaller than in the present study and will have even less impact on the outcome.

中文翻译：

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不准确的注视对基于 VEP 的视力估计的影响很小

目的

在怀疑装病的情况下，可使用基于 VEP 的视力评估来客观化主观抱怨。在这样的应用中，需要预料到缺乏合作。这同样适用于怀疑有功能障碍的幼儿。在本研究中，我们评估了不准确的固定如何影响使用 VEP 技术获得的视力估计值。

方法

基于 VEP 的敏锐度估计是通过使用“逐步扫描”协议通过一系列不同的检查大小进行刺激而获得的。16 名参与者在五种不同的注视条件下（刺激区域的顶部、底部、右侧和左侧边缘的中央注视和偏心注视）接受了正常和退化视力的测试。

结果

大多数偏心注视的个体视力估计值与中心注视的差异小于 0.1 logMAR，几乎所有估计值的差异小于 0.3 logMAR。偏心注视的中位数估计值仅略有不同（高达 0.08 logMAR），并且除了具有正常视力的顶部注视外，没有显着差异。然而，偏心注视的数据质量较低，这增加了无法从记录中得出敏锐度估计值的可能性。

结论

基于 VEP 的视力估计对偏心固定相对不敏感。常规应用中未注意到的中心固定偏差可能比本研究中的要小，对结果的影响甚至更小。