汉字视标视力表研究的焦点问题及其剖析

各种不同字、词、句特点设计的近视力表及其相关研究成果颇丰,并在临床中得到一定的应用.但以汉字为视标的近视力表颇有争议,主要是因为汉字构架的多样性使其难以达到基本视标的要求;汉字的认知在视标识别中起一定作用,增加了临床检测中如何确定其科学表达视力或视功能的复杂性.由此,一些学者对汉字为视标的近视力表的研究和应用价值提出质疑,本文将就相关争论焦点进行分析.     

两对比度中文阅读视力表的设计

选择可视性相似的句子作为视标,以完成两对比度中文阅读视力表的设计。方法实验研究。本研究通过视标的选择和视力表版面的制作完成两对比度中文阅读视力表的设计。通过以下方法选取可视性相近的句子作为视标。①句子的初步标准化：对日常阅读材料的各种文体进行句子长度的统计,得出常用书面文体的句子长度。以人教版初中语文课本的现代文为句子来源,根据所统计句子长度从2500个常用汉字中选取构建并适当修改句子。得到句长相同、字词难度相近、语意语法相近等要求95个汉语句子。②心理物理学测试：选择受过大学教育、远近矫正视力达1.0及以上、调节幅度正常、近期眼部无明显不适的受检者阅读这些句子,根据阅读速度和总笔画数这2个因素的最小范围最大交集的原则,选取视标。阅读视力表的版面设计采用国际通用的原则。在对比度上配置100%和10% 2种对比度。数据采用独立样本t检验和配对t检验进行分析。结果 经过初步筛选和心理物理学测试,最后选取可视性相近的52个句子作为视标,结合通用设计原则完成两对比度中文阅读视力表的设计。结论 两对比度汉字阅读视力表其视标之间的可视性相近,视力表设计特点标准科学,具有测量阅读视力、评价阅读行为等用途。     

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     

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.     

散光视标检查与散光轴位关系的定量推导

目的 定量推导散光视标检查与散光轴位之间的关系.方法 根据光学和数学的原理,从点光源成像入手,逐步定量地推导被检者对散光视标的辨认结果和散光轴位之间的关系.结果 被检者看到的最清晰散光视标的时钟钟点数乘以30°,即为被检者的散光轴位.或者被检者看到的最不清晰的散光视标的时钟钟点数加上3乘以30°,亦为被检者的散光轴位.结论 被检者对散光视标辨认结果和散光轴位之间关系的定量推导有助于正确的理解和临床应用.     

儿童彩色视力表的研制及应用

目的:研制一种儿童彩色视力表,并探讨其应用效果。方法:视力表设计采用视角原理,用彩色图形视标,各行视标间增率以几何级数(10槡10),即1.2589增加。11个彩色图形,共8行,检查距离3m,视力记录为五分记录和小数记录。以标准对数视力表为对照,用新的儿童彩色视力表检查4~6岁儿童100眼。结果:儿童彩色视力表和E字对数视力表检查,两组视力检查结果差异无统计学意义(t=1.2671,P>0.05),两组视力数据存在正相关(r=0.924,P<0.01)。合作率100%,对视标的识别率90%以上。结论:儿童彩色视力表儿童容易接受,具有可靠性,适用于儿童视力的检查。     

视力自动化检查系统的研制和临床应用

目的:为快速准确地检查视力,自行设计一台视力自动检查仪,并将其与传统视力表检查方法进行对照,探讨其临床应用的可行性。方法:开发视力自动化检测软件,使用液晶显示器(LCD)显示视标,被检者根据视标开口方向使用无线设备反馈信息,计算机将自动记录和处理被检者的反馈信息,同步显示被检者的视力检测结果,并在检查结束打印检查报告。同时使用传统视力表检查视力,对比两种检查方法的差异。结果:该软件系统的检测结果有极佳的可重复性,同时将该系统和常规视力表进行对比,发现两者视力检查结果无明显差异。结论:该系统可以快速准确地检测视力,可以推广应用于各级医院、学校和体检等机构,尤其适用于群体视力的检查。     

对国际标准试视力表印刷误差的测量和改进E字形视标设计的建议

试视力表视标的设计应合理和对印刷的要求应精确无误。印刷的视标清晰,对各行视标的大小应尽量达到或接近理论数值。视力表是根据视角的原理设计的。正常眼分辨最小物体的角度为一分视角,或称最小视角。一分视角相当于视网膜上4.96微米的     

不同对比度视力表及其临床应用

目的：介绍一种新的不同对比度视力表及其临床应用价值。方法：本视力表由３ 种不同对比度视力表和一种黑白反转视力表组成。对比度和视标大小均以几何级数变化,各表的视标和背景的亮度平均值保持一致。黑白反转视力表和第一视力表均为最高对比度,但产生较小眩光,可鉴别眼前段疾病。结果：应用本视力表检测了８７７ 人１７４８ 只眼,发现对比敏感度随年龄增长而下降,并因许多眼病而改变。结论：本视力表检查方便、快速,结果可靠,可常规应用于眼视光临床。     

对视力表的一点建议

我国目前普遍采用、由缪天荣教授设计的5分记录对数视力表具有较多优点。其中“E”字视标由直线组成,每个视标有3条横线和1条竖线(横置视标)或3条竖线和1条横线(竖置视标),尤其适用于散光的测试。该视力表于1990年被定为我国视力检测标准。但经多年应用,发现此视力表中对视标数目的安排略有不足。     

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.     

Design of an Arabic near visual acuity chart

This paper describes the design of an Arabic test chart for measurement of visual acuity at near. The chart was designed employing specially selected Arabic letters and was based on the logMAR principle devised by Bailey and Lovie, Ten Arabic letters of nearly equal legibility values (0.92–1.05) (mean = 1.00), (SD = 0.05) were used in the design of the chart. Each row of the chart has 5 letters and row legibility values range from 4.82 to 5.03 with a mean of 4.92 (SD = 0.06). The logMAR method of visual acuity scaling was used, hence the sizes of letters in the rows progress in a uniform step of 0.1 log unit. The inter letter spacing is equal to the width of each letter in the row, while inter–row spacing is equal to the height of letter in the subjacent row. The height of letters ranged from 3.67 to 0.46mm corresponding to visual acuity of 2.4 M to 0.3 M which is equivalent to reduced Snellen 6'36 to 6:4.5 at 0.4 m. The chart is designed for use at 40cm with a recommended luminance level of 160cd/m².     

An arabic letter distance visual acuity test chart for young children and illiterate adults

This paper describes the design of a kinetic response Arabic letter distance visual acuity test chart for young children and illiterate adults. An Arabic letter ein which has previously been used in the design of Arabic alphabet VA charts was employed. Four different orientations of the letter were constructed on a 5 x 5 unit format and graded according to log MAR principle of acuity scaling using an Apple computer. Inter-letter space in each row was made equal to the width of each letter in the row, and inter-row space was made equal to the height of letters in the next lower row. The chart has 14 acuity rows ranging from 4/40 to 4/2 (6/60 to 6/3) (20/200 to 20/10) (log MAR 1.0 to -0.3) at 4 metres. To establish the validity of the chart, acuity values obtained using the chart were compared with those from an existing Arabic log MAR distance VA chart and the Bailey and Lovie distance VA chart. Test retest reliability of the chart was also examined statistically. Results show that VA values from the new chart were significantly similar with those from which it was compared, and that values from the chart are reliable. The chart will be useful for evaluating vision, especially for young children and illiterate adults.     

Arabic near test chart for partially sighted patients

This paper describes the design of an Arabic alphabet near acuity chart for examination of partially sighted patients. The alphabets used have similar legibility values (0.92 to 1.05) (Mean = 1.00) (SD = 0.05) and each row of the chart has similar legibility values as the others. The LogMAR method of acuity scaling was used, therefore each row is larger in size than the preceding row by a constant value of 1.26 (0.1 log unit). The inter-letter space in a row is equal to the breadth of each letter in the row and the inter-row spacing is equal the height of letters in the subjacent row. The chart has 10 rows and visual acuity values range from 9.6 to 1.2 M (LogMAR 1.4 to 0.5) at 40 cm, corresponding to Snellen 6/144 to 6/18, 20/480 to 20/60. The chart will be useful for examining Arabic-speaking partially sighted subjects.     

Arabic visual acuity chart for low vision examination

An Arabic visual acuity chart has been designed for low vision examination, using ten Arabic letters constructed on a 5 × 5 framework. The chart contains seven pages with acuity values ranging from 20/600 to 20/80, corresponding to letter sizes of 26.5–3.5 cm. Interletter spaces were made one-fifth the size of each letter in a row while inter-row spaces were made equal to the height of the letters in the row below. The chart will be useful to eye care practitioners who may wish to use Arabic charts in low vision evaluation.     

Association between intensity of posterior capsule opacification and contrast sensitivity

PURPOSE: To investigate the correlation between change in contrast sensitivity (CS) and difference in objective posterior capsule opacification (PCO) score before and after Nd:YAG laser capsulotomy. DESIGN: Prospective interventional case series. METHODS: CS (Functional Acuity Contrast Test, or FACT, chart), distance visual acuity (Early Treatment Diabetic Retinopathy Study [ETDRS] chart), and pupil size of 30 pseudophakic eyes with PCO of varying intensity were measured before and after capsulotomy. Digital retroillumination images were taken, and the area corresponding to the pupil size was evaluated with an automated PCO analysis program known as AQUA. RESULTS: The correlation between change in PCO score and change in CS was highest (r = 0.85) for row B on the FACT chart and lowest (r = 0.09) for row E. The correlation with change in ETDRS visual acuity was 0.57. CONCLUSIONS: Objective PCO assessment by an automated image analysis system correlates well with PCO-induced loss of CS and is therefore an appropriate method for clinical studies on the development and prevention of PCO.     

Distance and near visual acuity in infantile nystagmus.

PURPOSE: Infantile nystagmus (IN) has been reported to decrease with convergence. However, previous studies reported equivocal results regarding a corresponding improvement in acuity with near viewing. The aim of this study was to determine whether visual acuity improves with near viewing in patients with IN. METHODS: In the first experiment, visual acuities were measured using clinical test charts at standard test distances of 3 or 6 m and 40 cm and using S Charts at 3.75 m and 40 cm. In the second experiment, visual acuities were measured using a Bailey-Lovie chart at distance and a Lighthouse modified ETDRS near card held by each subject at his or her preferred working distance. S-chart acuities were obtained again at 3.75 m and 40 cm for comparison. Horizontal eye movements were recorded using infrared limbal reflection for 20 of the 34 subjects in the first experiment and for all 20 subjects in the second experiment. RESULTS: The S-chart acuities measured at distance and near were almost all within 0.1 logMAR (logarithm of the minimum angle of resolution) in experiments 1 and 2. Clinically measured acuity averaged nearly one line better at 40 cm than at distance in experiment 1, but the mean difference between near acuity using the ETDRS card and distance acuity using the Bailey-Lovie chart was less than one letter in experiment 2. No consistent relationship existed between the changes in visual acuity with viewing distance and the subject's eye movements. CONCLUSION: Despite a reduction of nystagmus at near distances in many patients with IN, the visual acuity at near does not improve significantly. These results imply that visual acuity in patients with IN is determined primarily by sensory limitations rather than by the moment-by-moment characteristics of these patients' eye movements.     

阅读中文简体字与繁体字人眼短暂性近视量及其回退时间的差异

目的 研究正视人群与近视人群阅读中文简体字与繁体字时产生的短暂性近视的量,以及其回退时间的差异.方法 实验研究.随机选择18～28岁的近视者18人,等效球镜度为(-3.74±1.22)D;正视者18人,等效球镜度为(-0.14±0.22)D.应用Grand-Seiko WAM-5500分别测量阅读两种大小(12 pt;8 pt)中文简体字与繁体字4组视标短暂性近视的量及其回退时间,要求阅读距离40 cm(调节需2.5 D),每组视标阅读时间为5 min.结果 阅读繁体字,近视组的短暂性近视量为(0.61±0.34)D,大于正视组短暂性近视量(0.42±0.25)D (t=2.556,P＜0.05);近视组阅读繁体字短暂性近视的量为(0.61±0.34)D大于简体字短暂性近视的量(0.53±0.33)D (t=2.298,P＜0.05),正视组阅读两种不同字体差异无统计学意义(t=0.789,P＞0.05).阅读引起近视组短暂性近视回退时间为(15.88±19.53)s,大于正视组的短暂性近视回退时间(9.04±12.62)s,差异有统计学意义(t=2.555,P＜0.05);但阅读各组视标间近视组和正视组短暂性近视回退时间差异无统计学意义.结论 从短暂性近视方面研究,阅读中文繁体字与简体字引起的短暂性近视的量存在差异,近视组更容易受到阅读不同字体的影响,这种不同的阅读字体引起不同的短暂性近视量可能是近视发生率地域性差异形成的一种环境因素.