Lam Andrew K C, Tong Cecilia, Tse Jimmy, Yu Man
School of Optometry, The Hong Kong Polytechnic University, Hong Kong SAR, China.
Clin Exp Optom. 2008 Sep;91(5):447-52. doi: 10.1111/j.1444-0938.2007.00235.x.
The aim of this study was to determine the repeatability of high- and low-contrast visual acuity (VA) measurements at near.
Fifty-five normal subjects were recruited. Inclusion criteria included visual acuity of at least 0.00 logarithm of minimum angle of resolution (logMAR) on each eye at distance. One eye was selected for this study, either the one with a better acuity or randomly chosen if there was no difference between the two eyes. Near VA was measured in a random order with the PolyU high-contrast (PolyU-HC), the PolyU low-contrast (PolyU-LC), the Precision high-contrast (P-HC) and the Precision low-contrast (P-LC) charts at 400 mm. Measurements were repeated after one to two weeks. Repeatability was presented using the 95% limits of agreement between visits.
The between-visit repeatability was +/-0.063 logMAR for high-contrast and +/-0.141 for low-contrast using the PolyU charts. The between-visit repeatability was +/-0.120 logMAR for high-contrast and +/-0.110 for low-contrast using the Precision charts. Seventeen subjects had high-contrast VA better than -0.10 logMAR using Precision chart, which could not be measured by PolyU chart. The mean difference between high- and low-contrast VA was 0.108 from the Precision charts (median difference of 0.10 or one line).
The Precision charts could measure high-contrast near VA to threshold level. Practitioners should be aware of a VA difference of more than one line in repetitive measurement, at both high and low contrast. A difference in near high- and low-contrast VA of more than one line may warrant further investigation.
本研究旨在确定近视力时高对比度和低对比度视力（VA）测量的可重复性。
招募了55名正常受试者。纳入标准包括每只眼睛在远距离时的视力至少为0.00最小分辨角对数（logMAR）。本研究选择一只眼睛，若两只眼睛视力无差异，则选择视力较好的那只眼睛，否则随机选择。在400毫米距离处，使用香港理工大学高对比度（PolyU-HC）、香港理工大学低对比度（PolyU-LC）、Precision高对比度（P-HC）和Precision低对比度（P-LC）视力表以随机顺序测量近视力。一到两周后重复测量。使用两次检查之间的95%一致性界限来表示可重复性。
使用PolyU视力表时，高对比度的两次检查之间可重复性为±0.063 logMAR，低对比度为±0.141 logMAR。使用Precision视力表时，高对比度的两次检查之间可重复性为±0.120 logMAR，低对比度为±0.110 logMAR。17名受试者使用Precision视力表时高对比度视力优于-0.10 logMAR，而使用PolyU视力表无法测量。Precision视力表显示高对比度和低对比度视力之间的平均差异为0.108（中位数差异为0.10或一行）。
Precision视力表可以将高对比度近视力测量到阈值水平。从业者应注意在重复测量中，高对比度和低对比度下视力差异超过一行的情况。近高对比度和低对比度视力差异超过一行可能需要进一步调查。
