Measurement of visual acuity with two different charts; a comparison of results and repeatability in patients with cataract

Purpose: To compare two different optotypes to measure visual acuity. Methods: Experiment 1: Fifty patients with moderate cataracts were asked to read a chart consisting of letters of the alphabet (Sloan letters) first and a chart comprising Landolt's broken rings afterwards. Experiment 2: Half of patients were instructed to repeat the reading with a second letter chart, the other half was instructed to read the chart with the broken rings again. Results and conclusions: Experiment 1: It was found that with the letter chart more optotypes (two to four) were recognized than with the broken ring chart. The different result of visual acuity measurement with the two optotypes is irrespective of the visual acuity. Experiment 2: The re-read instruction revealed that the measurements were reproduced equally for both charts.     

基于傅里叶频谱分析设计的汉字近视力表

本研究介绍一种汉字近视力表。本视力表将傅里叶频谱分析和心理物理学测试应用于汉字视标的选择,筛选出可视性相似的汉字作为同一张视力表的视标。在视力表的设计中,每行视标的个数保持一致,每相邻两行视标之间的行间距为下一行视标的高度,每一行的字间距为该行所在字的字宽,视标的增率采用0.1对数单位,增加可重复测试的小视标及低对比度视力表等。因被检者的阅读习惯距离存在差异,故规定标准检查距离为40cm的同时设置25cm作为备选测量距离。将它应用于常规测试对预测被检者辨认汉字的阈值和早期发现与视觉有关的眼病有一定的临床价值。     

Legibility variations of Chinese characters and implications for visual acuity measurement in Chinese reading population

PURPOSE: Written Chinese contains an enormous number of characters with a wide range of spatial complexities. Consequently, the legibility of Chinese characters is expected to vary significantly, and this variability offers the challenge of deriving a simple visual function measurement for the Chinese reading population. The purpose of this study was to suggest a solution to the challenge through psychophysical studies of Chinese character legibility. METHODS: To illustrate legibility variations in Chinese characters, visual acuities for six groups of Chinese characters from low to high spatial complexities and one group of Sloan letters were determined in six normal-sighted Chinese observers. The relationship between legibility and optical defocus were then determined for the Landolt C, the Snellen E, and three groups of Chinese characters representing low, medium, and high spatial complexities in 26 normal-sighted Chinese readers. RESULTS: The acuity size of Chinese characters increased steadily with stimulus complexity, though at a slower rate than would be expected if visual acuity were based on the finest details of the stimuli. The acuity size versus optical defocus functions of three Chinese character groups and the Snellen E had similar slopes and differed only by a vertical shift, depending on the optotype spatial complexity. The function of the Landolt C was significantly steeper. CONCLUSIONS: The findings indicate that visual acuity assessment in Chinese readers is complicated by the spatial complexity of Chinese characters, but the fact that the Snellen E, which is the current national standard of acuity measurement in China, and Chinese characters showed similar dependence on optical defocus may indicate a potentially valid way to infer functional vision in Chinese readers with Snellen E acuity.     

将图像傅里叶频谱分析应用于汉字视标的选择

目的 以汉字图像各空间频率的频谱能量相似为原则,筛选汉字作为汉字视力表的备选视标.方法 从2500个常用汉字中选取两类笔画数的汉字:少笔画数汉字(2、3、4画,共172个)和中笔画数汉字(7、8.9画,共890个).将其中的每个汉字制作成BMP图片格式.然后,利用傅里叶频谱分析,获取每个汉字图像各空间频率成分的频谱分布.以此分别对所有的少笔画数和中笔画数汉字的各空间频率的频谱能量求均值,将其作为参照值,采用聚类分析将汉字图像进行聚类来选取汉字.结果 与少笔画数和中笔画数汉字各空间频率的频谱能量均值相似的汉字分别为50和40个.结论 通过汉字图像的傅里叶频谱分析,以汉字图像的各空间频率的频谱能量相似作为筛选视标的主要原则,符合了视觉系统具有的傅里叶频谱分析特性.此方法应用于汉字视标的筛选具有重要的意义.     

心理物理学方法在汉字视标选择中的应用

目的 在傅里叶频谱分析的基础上,采用心理物理学方法确定汉字视标的可视性,获得视标物理刺激均等与心理反应均等的异同,确定心理物理学方法在汉字视标选择中的重要作用.方法 28位志愿者,裸眼视力或最佳矫正视力为-0.11±0.06(LogMAR值).分别从汉字图像傅里叶频谱分析所得到的50个各空间频率的频谱能量均值相似的少笔画汉字和40个中笔画汉字中筛选出尽可能包含横、竖、撇、捺结构的中性少笔画和中笔画汉字17个和20个作为备选视标.分别将以上少笔画汉字和中笔画汉字的平均视敏度阈值作为参考值,每个汉字制作成6种字体大小的汉字图片.取所有被试对每个汉字图片在不同字体大小时的辨认准确率的平均值,并用韦伯函数(Weibull function)进行拟合,得到字体大小--辨认准确率曲线,并获取每个汉字的阈值大小(tb值)和斜率(β值).结果 17个少笔画汉字的阈值大小为6.16±0.54(单位:分),斜率为5.91±2.18;20个中笔画汉字的阈值大小为8.20±0.71(分),斜率为11.18±3.55.以阈值大小最接近且斜率尽可能接近为筛选指标,最终确定可视性相似的10个少笔画汉字和10个中笔画汉字.选做少笔画汉字视力表视标的汉字为"斤、长、文、尺、万、月、又、不、才、卫"(tb值为5.84±0.36,β值是4.72±0.85),选做中笔画汉字视力表视标的汉字为"孩、郑、怪、构、肾、择、染、秋、软、祝"(tb值为8.38士0.24,β值是10.47±3.9).结论 傅里叶频谱分析方法可以非常客观地从众多汉字中选择出物理刺激相等的汉字,由于汉字视标之间相似的可视性同时表现为视标的物理刺激相似和心理反应的一致性,因此汉字视标的最终选择还需要进行心理物理学的测试.

Abstract：

Objective This study investigated the legibility in use of psycho-physical methods to select Chinese characters for visual acuity charts. Methods Twenty-eight subjects with the raw visual acuity or best corrected visual acuity of - 0. 11 ± 0. 06 ( LogMAR) were recruited for this study. Ninety Chinese characters with similar Fourier frequency spectrum were used as candidates for the selection of visual targets.Thirty-seven Chinese characters with each consisted of horizontal, vertical and oblique strokes were selected from these candidates. Six different-sized BMP images for each selected Chinese character were made based on the average visual acuity threshold of all the selected characters. The accuracy rate for all subjects to read each size of the BMP images was averaged. Graphs correlating the font sizes with the accuracy rates were formed using Weibull function imitation, which provided a visual acuity (VA) threshold and slope for each Chinese character selected. Results Among the 37 Chinese characters selected, 17 had a VA threshold 6. 16 ±0. 54 (unit: arc) and 20 had a VA theshold of 8. 20 ±0. 71. The slope for characters with low stroke number and medium stroke number was 5.91 ± 2. 18 and 11. 18 ± 3.55, respectively. Based on the finally determined as the visual targets for a lower stroke-number Chinese visual acuity chart (tb: 5. 84 ±β: 10. 47 ±3. 9) were determined as the visual targets for a medium stroke- number Chinese visual chart. Conclusion Analysis using Fourier frequency spectrum provides an objective method in the selection of Chinese characters for Chinese visual acuity charts. A psychological test for this selection would further confirm the legibility of the method used in this study.     

低视力对数视力表的研制

目的 :研制一种适合我国眼科临床使用的低视力对数视力表。方法 :根据Baily Lovie的LogMAR视力表和我国标准对数视力表的设计标准和原理设计 ,1分视角为 1.0视力 ,视标的增率为 10 10 ,视标的间距和行距与我国标准视力表相同 ,E字母设备 ,每行视标个数与Baily Lovie的视力表一致。为了与低视力分级标准一致 ,采用小数记录。结果和结论 :低视力对数视力表 ,设计合理 ,检查低视力的范围大 ,将应用于我国眼科临床     

对数视力表认识误区之管见

针对近年来有关视力标准的争议提出看法：①形觉视力标准的制定．应覆盖整个形觉视力范围。②Weber—Fechner法则至今仍是心理物理学领域包括视觉领域的指导理论。③发现对数视力表视标增率和黄金比率的关系：10√10≈√φ。说明对数视力表的设计无形中巧合了黄金比率规律。④分析了小数制和对数制两种视力数制的优缺点,认为应弃用小数制。     

A new Gujarati language logMAR visual acuity chart: Development and validation

Aims:

Gujarati is the main spoken language of a large proportion of the population of India. The aim of this study was to develop and validate a new Minimum Angle of Resolution (logMAR) visual acuity chart in the Gujarati language.

Materials and Methods:

A new Gujarati visual acuity chart was designed to logMAR specifications using Gujarati optotypes experimentally selected to have similar relative letter legibility under spherical and cylindrical defocus. The chart validation study was carried out using 153 adult subjects in a large clinical setting in India. Subjects who were literate in English and Gujarati participated in the study. Visual acuity was measured with the new Gujarati logMAR chart and a modified Early Treatment of Diabetic Retinopathy Study-(m-ETDRS) logMAR chart. The method of presentation was randomized between the charts. Repeat visual acuity was measured on a subsequent day with a second version of the Gujarati logMAR chart.

Results:

The Gujarati chart correlated highly with the m-ETDRS logMAR chart (r² = 0.974). The mean visual acuity difference (Gujarati – m-ETDRS logMAR) was equal to three letters (–0.06 logMAR). The Gujarati logMAR chart also proved to be highly repeatable (r² = 0.994, test-retest) with 95% CI of ± 0.04 logMAR.

Conclusions:

The new Gujarati logMAR visual acuity chart provides a valid and repeatable tool for the measurement of visual acuity in native Gujarati language speakers.     

国家视力表的标准化问题

视力表在招生、招工、普查及眼科临床和科研中是非常重要而又十分常用的一个工具。迄今为止,视力表的设计已越来越趋向成熟,各国在视力表设计的核心内容方面基本趋向标准化。但人们在视力表的选择、设计和应用方面仍有一些困惑,笔者仅就国际上的视力表和我国国家标准对数视力表的发展历史、视力表设计的核心内容以及目前视力表使用中存在的问题进行述评,以避免在视力表选择和应用中存在的误区,使之更好地应用于视力普查、眼科临床和科研等各领域。     

正视眼和近视眼在明暗环境中不同对比度的视力比较

目的正视眼和近视眼人群在明暗环境中不同对比度时的视力的对比研究。方法134例受试者,按屈光不正度数分成正视组、低度近视组、中度近视组和高度近视组。先主觉验光,再用卡洞法找出优势眼,屈光矫正后应用多功能视力测量仪检测优势眼在明和暗环境中不同对比度视力。结果高度近视组在明和暗环境中不同对比度时视力均较其它3组差,与正视组比较有显著性差异(P<0.05)。随着近视屈光度的增加,在明和暗环境中不同对比度时视力呈现下降趋势。在相同对比度下,明环境中的视力好于暗环境中的视力。在相同环境下,随着对比度的下降,视力随之下降。结论框架眼镜矫正时高度近视眼视觉质量明显差于正视眼及低中度近视眼。其视力受环境照明及对比度差异的影响。     

Automated visual acuity testing

We describe a new computre-based method for testing visual acuity. The software operates in the Window 3.1^TM enviroment. An IBM compatible PC generates characters on the computer's moniter with the standard SVGA or VGA video graphics card. The testing paradigm utilises a staircase to determine the 50 per cent acuity level and requires an average test time of 80 seconds. Comparisons with standard clinical charts show that the test allows a reasonbale estimationof visual acuity. The avilability of different psychometric methods makes this applicaiton particularly suited to clinical trials or for the deteciton of early change in acuity. Other features availbale with this software, including low contrast optotypes and phootstess testing, are also described.     

Contrast visual acuities in cataract patients. I. Comparison with normal subjects.

Contrast sensitivity and glare sensitivity are often abnormal in cataract patients. However, despite significant subjective complaints, relatively good visual acuities often are obtained with high-contrast optotypes. Using Variable-Contrast Visual Acuity Charts (VCVAC), we measured visual acuities of 40 eyes of 24 normal subjects (visual acuity greater than or equal to 1.0) aged 41 to 72 years, and 40 eyes of 28 cataract patients (visual acuity greater than or equal to 0.6) aged 44 to 81 years. The VCVAC consists of 4 different charts (1-4). The contrast is 90% in charts 1 and 4, 15% in chart 2 and 2.5% in chart 3. Chart 4 is the reverse polarity of chart 1. The decrease of visual acuity compared with the high-contrast chart (chart 1) was larger in the cataract group with both in the 15% contrast (0.52 vs. 0.71 octave) and the 2.5% contrast (1.21 vs. 1.75 octaves). In cataract group, 23/40 eyes (57.5%) showed better visual acuity with chart 4 than that of chart 1. In addition to high-contrast optotypes, acuity measurements using intermediate- to low-contrast optotypes, combined with the reverse polarity chart, seem effective in analyzing the visual disabilities caused by early cataract.     

阶梯渐进衍射型非球面多焦点人工晶状体植入术后的视觉质量研究

目的 观察阶梯渐进衍射型非球面多焦点人工晶状体（AcrySof ReSTOR SN6AD1和SN6AD3）植入术后的视觉质量.方法 前瞻性病例系列研究.连续选取2009年6月至2010年4月于中山眼科中心收治的60例年龄相关性白内障患者,男29例,女31例,年龄为50～79岁.所有患者均行超声乳化白内障摘除联合人工晶状体植入术.按照植入人工晶状体的不同分为三组：SN6AD1多焦点人工晶状体组（20例,40眼）,SN6AD3多焦点人工晶状体组（20例,40眼）及SN60WF单焦点人工晶状体组（20例,40眼）.术后3个月,观察患者裸眼近视力、高低对比度裸眼中视力、裸眼远视力、裸眼汉字近视力、对比敏感度、最适阅读距离及阅读速度.对相关数据进行one-way ANOVA检验、Bonferroni比较、秩和检验或t检验.结果 裸眼近视力：SN6AD1组及SN6AD3组分别为（0.074±0.862）logMAR和（0.075±0.772）logMAR,明显优于SN60WF组[（0.351±0.691）logMAR],差异有统计学意义（Z=-6.756,P=0.000 Z=-6.508,P=0.000）.裸眼中视力：40 cm距离处的高、低对比度裸眼中视力比较,三组之间差异有统计学意义（x2=29.085,P=0.000 F=9.672,P=0.000） 63 cm处的高、低对比度裸眼中视力比较,三组之间差异有统计学意义（x2=14.869,P=0.001 x2=8.018,P=0.018） 而100 cm处高、低对比度裸眼视力比较,三组间差异均无统计学意义（F=1.917,P=0.152 X2=5.408,P=0.067）.裸眼远视力：三组之间差异无统计学意义（x2=1.555,P=0.460）.裸眼汉字近视力：除少笔画低对比度情况外,SN6AD1组与SN6AD3组单、双眼的高、低对比度汉字近视力均优于SN60WF组,差异有统计学意义（P均＜0.05）.对比敏感度：在明光、暗光、明光眩光、暗光眩光时,SN6AD1组与SN6AD3组中低空间频率对比敏感度稍低于SN60WF组,差异有统计学意义（P均＜0.05）.最适阅读距离和阅读速度：SN6AD1组、SN6AD3组和SN60WF组的最适阅读距离分别为（38.5±3.1）、（32.8±3.9）、（47.6±4.7）cm 阅读速度分别为（173.7±58.1）、（179.3±23.6）和（106.9±31.0）字/分,SN6AD1组和SN6AD3组均较SN60WF组快,差异有统计学意义（Z=-3.423,P=0.001 Z=-4.522,P=0.000）.结论 SN6AD1和SN6AD3多焦点人工晶状体可以提供较SN60WF单焦点人工晶状体更好的近视力、40 cm及63 cm高低对比度裸眼中视力,以及更舒适的阅读距离和更快的阅读速度.SN6AD1人工晶状体能提供较SN6AD3更优秀的40 cm及63 cm高低对比度中视力.     

High contrast and low contrast visual acuity in age related macular degeneration*

Low contrast Bailey-Lovie visual acuity (LCBL) and high contrast Bailey-Lovie visual acuity (HCBL) were measured in subjects with age-related macular degeneration (ARM) and subjects with normal visual function. Low and high contrast visual acuities and the difference between low and high contrast acuities were significantly different for the ARM group compared with the normals, confirming previous findings of disruption to contrast discrimination in ARM. The high contrast Bailey-Lovie chart was found to be a useful screening device for macular degeneration using a pass/fail criterion of 6/7.5. Pre-ARM (PARM) subjects can be defined as those with drusen and/or pigmentary disturbance and high contrast acuity of better than 6/7.5. However, the low contrast chart used at normal clinical illuminances is of no additional diagnostic value in ARM.     

The set of variable- contrast visual acuitycharts and its clinical application

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Analysis of errors in letter acuity measurements

This study examined the possibility of increasing the precision of letter visual acuity measurements by investigating the basis for two methods of fractional grading of responses. The first method concerns the varying legibility/readability of letters and the second is concerned with the recognition of two classes of errors, those that are completely wrong (for example, O for H) and those that are partially wrong, because they are reasonable substitutes for the correct letter when the incorrect response has significant shape features in common with the correct letter (for example, N for H). Errors made when visual acuity is measured were analysed for two samples of 200 subjects, each group viewing a different version of the Bailey-Lovie letter chart. Varying legibility and readability for the 10 letters used to construct these charts have been demonstrated, the most common errors occurring for F, H, and V, and the least common errors occurring for U and Z. Chi-square tests indicated that incorrect letter responses are not randomly distributed (p < 0.001) for all chart letters. The most common reasonable substitutes found were P for F, Yfor V, F for P, H for N, N for H, O for D, B and R for E and P for R. The conclusion is drawn that the potential for finer scaling of letter acuity measurements that accounts for varying legibility and readability of letters and discriminates between completely wrong responses and partially correct responses (reasonable substitutions) has been demonstrated. We propose that the weighting of responses according to these mechanisms for finer scaling may increase the precision of letter chart measurement of visual acuity as an aid to scientific investigation as well as to the monitoring of visual function in clinical practice. The use of a detailed weighting system would be facilitated by computer assisted calculations and will be the subject of a future report.     

正视眼波前像差与低对比度视力相关性研究

目的 分析正视眼波前像差与低对比度视力的相关性.方法 对95例(95眼)健康正视眼用WASCA(wavefront supported corneal ablation)波阵面像差仪测眼波前像差,对瞳孔6 mm时第2,3,4阶像差的各项Zernike函数(C3-C14)进行分析.用多功能电子视力测量仪检测亮、暗环境中对比度为10﹪和5﹪时的裸眼视力和最佳矫正视力.用多元线性回归分析眼波前像差与各低对比度视力间的相关关系.结果 离焦像差(C4)与亮、暗环境中对比度为10﹪和5﹪时的裸眼视力间的直线相关关系有统计学意义(P＜0.01);水平彗差(C8)与亮、暗环境中对比度为10﹪和5﹪时的最佳矫正视力间的直线相关关系有统计学意义(P＜0.01).其余Zernike 函数与各低对比度视力间的直线相关关系均无统计学意义(P＞0.05).结论 正视眼的波前像差与低对比度视力有关,其中离焦像差与裸眼视力有关,水平彗差与最佳矫正视力有关.     

新型对数视力表与“C”形对数视力表的一致性与稳定性分析

目的评价新型对数视力表与具有8个方向视标选项的“C”形对数视力表之间的一致性与稳定性。方法 横断面研究。对48例应届高中毕业生分别进行新型对数视力表与“C”形对数视力表的视力检查,采用组内相关系数（ICC）和Cronbach′s Alpha系数分析视力测量结果的重复性,采用Bland-Altman分析一致性。结果 “C”形对数视力表Cronbach′s Alpha系数在0.8以上,ICC接近0.9,新型对数视力表Cronbach′s Alpha系数接近0.8,ICC＞0.75,均显示较好的重测稳定性。2种视力表第1次和第2次视力测量均具有较好的一致性,95％一致性界限分别为（0.173,-0.133）logMAR和（0.198,-0.116）logMAR。结论 新型对数视力表检查结果稳定,和“C”形对数视力表一致性较好。     

A new specialized visual acuity chart for amblyopic children aged 3-5 years old:development and its clinical applications

AIM: To introduce a new specialized visual acuity chart for amblyopic children aged 3-5 years old and its clinical applications.METHODS:The new visual acuity chart and notations were designed based on Weber-Fechner law. The optotypes were red against a white background and were specially shaped four basic geometric symbols:circle, square, triangle,and cross. A regular geometric progression of the optotype sizes and distribution was employed to arrange in 14 lines. The progression rate of the optotype size between two lines was 1.2589 and the testing distance was 3m. Visual acuity score could be recorded as logMAR notation or decimal notation. Age-stratified diagnostic criteria for amblyopia established by consensus statement on diagnosis of amblyopia (2011) among members of the Strabismus and Pediatric Ophthalmology Group, Ophthalmology Society, Chinese Medical Association (SPOGOSCMA) were illustrated in the new visual acuity chart.RESULTS: When assessing visual acuity in children aged 3-5 years old, this new visual acuity chart that consists of four symmetrical shapes (triangle, square, cross, and circle) overcame an inability to recognize the letters of the alphabet and difficulties in designating the direction of black abstract symbols such as the tumbling ‘E’ or Landolt ‘C’, which the subjects were prone to lose interest in. The visual acuity score may be recorded in different notations:decimal acuity and logMAR. These two notations can be easily converted each other in the new eye chart. The measurements of this new chart not only showed a significant correlation and a good consistency with the international standard logarithmic visual acuity chart (r=0.932, P<0.01), but also indicated a high test-retest reliability (89% of retest scores were within 0.1logMAR units of the initial test score).CONCLUSION: The results of this study support the validity and reliability of distance visual acuity measurements using the new eye chart in children aged 3 to 5 years over a wide range of visual acuities, and the new eye chart is great for early detection of amblyopia. It can be applied in various clinical settings.     

English sentence optotypes for measuring reading acuity and speed—the English version of the Radner Reading Charts

Purpose

To develop 28 short sentence optotypes for the English version of the Radner Reading Charts that are as comparable as possible in number and length of words, as well as in difficulty and syntactical construction.

Methods

Thirty-four English sentences were constructed following the method used for other Radner Reading Charts to obtain “sentence optotypes” with comparable structure and the same lexical and grammatical difficulty. Best comparable sentences were statistically selected and standardized in 50 volunteers. Reading speed and the number of errors were determined. Validity was analyzed with a 124-word long 4th-grade paragraph of the Florida Comprehensive Assessment Test®. Computerized measurements of reading parameters were performed with the RADNER Reading Device (RAD-RD©; in conjunction with a PC and microphone).

Results

The mean reading speed obtained with the 28 selected short sentences was 201.53?±?35.88 words per minute (wpm), as compared to 215.01?±?30.37 wpm for the long paragraph. The mean reading times were 4.30?±?0.79 s and 35.26?±?4.85 s, respectively. The mean number of reading errors was 0.11?±?0.34. The correlation between the short sentences and the long paragraph was high (r?=?0.76; p?<?0.05; n?=?50). Reliability analyses yielded an overall Cronbach’s alpha coefficient of 0.9743.

Conclusion

The present study indicates that the 28 selected English sentence optotypes are comparable in terms of both lexical difficulty as well as in reading length, and it demonstrates the validity and reliability of such sentences as test items for determining reading parameters such as reading acuity and speed.