A novel high-frequency visual acuity chart

A high-frequency eye test chart using letters or figures of alternating black and white stripes (or dots) on a grey background was developed. Any cross-section of the letters has a Fourier transform with a zero frequency component equal to the luminance of the grey background. When the letters are out of focus, their image on the retina fades rapidly into the grey background, rendering them invisible rather than merely blurred as in a standard chart. The chart was calibrated by simulating refractive errors with defocusing lenses applied to a photographic camera and to subjects' eyes. No constant ratio was found between the size of the Snellen letters and the size of the high-frequency letters for equal visibility. The new chart requires letters for 20/200 acuity to be only 3.6 times larger than those for 20/20 vision. Results confirm the arbitrary nature of the Snellen fraction and warn about the accuracy of visual acuity determined by using charts of different letter types, calibrated by Snellen's system.     

Sweep visual evoked potential grating acuity thresholds paradoxically improve in low-luminance conditions in children with cortical visual impairment

PURPOSE: Children with cortical or cerebral visual impairment (CVI) often experience photophobia. In a study conducted to test whether this clinical phenomenon affects visual function, the sweep visual evoked potential (VEP) was used to evaluate cortical responses to grating stimuli in two luminance conditions: low and normal. METHODS: Twenty children (age range, 7 months to 4 years 10 months) with CVI and 17 age-matched control subjects were examined. Testing conditions consisted of a swept grating stimulus shown against a normal background luminance (109 cd/m2) and against a low-luminance background (20 cd/m2). Thresholds in these two luminance conditions were compared. Response amplitudes across the spatial frequency domain were also compared. RESULTS: Children with CVI paradoxically have improved grating acuity thresholds when the stimulus is shown using a low-luminance background (P=0.006). Response amplitudes are also increased in low luminance. In control children, luminance had no significant effect on response amplitudes or thresholds. CONCLUSIONS: Increased luminance causes a worsening of acuity thresholds in children with CVI. Response amplitudes are also diminished in normal luminance. This finding has implications for optimal viewing and learning conditions for children with CVI.     

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.     

Screening for myopia and refractive errors using LogMAR visual acuity by optometrists and a simplified visual acuity chart by nurses.

PURPOSE: To compare the sensitivity and specificity of a widespread method of screening for refractive errors in Singapore schoolchildren using a simplified acuity screening chart with a more rigorous method using the Early Treatment Diabetic Retinopathy Study (ETDRS) chart. A secondary aim is to estimate the best cutoff values for the detection of refractive errors using these two methods. METHODS: This is a population-based study, involving 1779 schoolchildren from three schools in Singapore. Logarithm of the minimum angle of resolution (logMAR) visual acuity was recorded using a modified Bailey-Lovie chart by trained optometrists, and visual acuity measurement was also undertaken using a simplified 7-line visual acuity screening chart by school health nurses. The main outcome measures were the receiver-operating characteristics (ROC's) of logMAR and the simplified screening visual acuity to detect myopia or any refractive errors. The difference between measurements, simplified screening visual acuity--logMAR visual acuity, was calculated. RESULTS: The optimal threshold using the simplified screening visual acuity chart for the detection of myopia or any refractive error was 6/12 or worse. Using logMAR visual acuity, the most efficient threshold for the detection of myopia was 0.26, but this was 0.18 for the detection of any refractive error. The area under the ROC curves was significantly greater in the case of the logMAR visual acuity measurement compared with the simplified screening visual acuity measurement for the detection of myopia or any refractive errors. The 95% limits of agreement for the two methods (simplified screening--logMAR acuity) was -0.219 to +0.339. CONCLUSIONS: Bearing in mind that the visual acuity measurements were performed by two different groups of professionals, visual acuity screening using the ETDRS method appears to be more accurate than the simplified charts for the detection of myopia or any refractive errors in children.     

Lea Symbols视力表在42～78个月儿童视力检查中的重复测量可信度分析

目的：探讨Lea Symbols视力表在学龄前儿童视力检查中的重复测量可信度。方法：横断面研究。 2017年4-5月对泉州市泉港区实验幼儿园的250名42～78（61.9±10.3）个月的学龄前儿童进行全面 的眼科检查,使用Lea Symbols视力表重复测量右、左眼的单眼远视力,采用LogMAR记录法记录 视力值。采用Bland-Altman分析、加权Kappa检验、组内相关系数3种统计分析方法衡量2次测量之 间的重复测量可信度。结果：3种分析方法均显示Lea Symbols视力表在学龄前儿童视力检查中的重 复测量可信度较好,2次测量间视力的差值94.3%在1行以内,2次测量的视力值之间的相关性较高 （r=0.753,P<0.001）。在139名屈光正常儿童中,2次测量的视力值（LogMAR）平均相差0.014。在 139名屈光正常儿童中,视力与月龄的相关性是显著的,月龄越大视力越好（r第1次=-0.335,P<0.001; r第2次=-0.424,P<0.001）;性别对可重复性没有影响（P=0.197）。结论：Lea Symbols视力表可用于 中国42个月及以上学龄前儿童的视力检查,可以在临床视力检查中推广使用。     

拥挤Kay图片视力表在学龄前儿童视力筛查中的应用

目的：采用拥挤Kay图片视力表检测学龄前儿童视力,并和标准对数视力表检测结果进行比较,探讨2种视力表检测结果是否具有一致性,以补充不能完成标准对数视力表检测的学龄前儿童的视力筛查。方法：前瞻性自身对照研究。于2021年1─5月随机选取济南市章丘区某幼儿园152名学龄前儿童进行全面眼科筛查,分别使用拥挤Kay图片视力表及标准对数视力表对其进行视力检测,并采用Wilcoxon检验进行2种视力差异性的比较,Spearman秩相关分析及Bland-Altman分析进行相关性及一致性分析。结果：152名儿童参与筛查,其中129名儿童屈光状态正常且能配合2种视力表检测。129名儿童中男74名,女55名,年龄为（52.3±7.0）个月;拥挤Kay图片测得LogMAR视力为0.10（0.09,0.10）,标准对数视力表视力为0.10（0.10,0.22）;2种视力检查方法有较好的相关性（r=0.436,P<0.001）,拥挤Kay视力表检测结果略高于标准视力表约0.04 LogMAR,差异有统计学意义（Z=-6.124,P<0.001）,Bland-Altman散点图显示98.4%的点均在一致性范围内;参与筛查儿童Kay图片视力检查配合度更高（χ2=18.007,P<0.001）。不同月龄拥挤Kay图片视力检测结果差异有统计学意义（H=13.791,P=0.003）,随年龄增长,视力呈递增趋势。结论：拥挤Kay图片视力表用于学龄前儿童视力检测,患儿配合程度高,其结果与标准对数视力表相比有较好的一致性,但Kay图片视力表所检查的视力结果高于标准视力表约0.04 LogMAR,在参考视力结果时应相应调整视力标准。     

两种视力表检查89位学龄前儿童视力的对比研究

目的比较学龄前儿童Lea Symbols与Tumbling E两种视力表的检测率、单眼视力值．建立3。4周岁儿童正常的视力值。方法招募温州市区29—53月龄的89名学龄前儿童，入选标准是身体一般情况良好。智力发育正常，除屈光不正外无其他眼病。以随机顺序用两种视力表检查儿童单眼视力，用间插的logMAR记分方法记录结果。招募23名成人志愿者，分别用两种视力表检查单眼视力．获得两者之间的换算关系。结果成人44眼Lea Symbols的平均视力比Tumbling E高0．02logMAR。89名儿童Lea Symbols视力表的检测率为88％．而Tumbling E视力表的检测率为65％，统计学分析两者差异有显著性（P〈0．01）。60位儿童中115眼能同时配合查Lea Symbols与Tumbling E,Lea Symbols的平均视力为0．17±0．09．Tumbling E的平均视力为0．25±0．09．两者作配对t检验差异具有显著性（P〈0．01）。两种视力表视力相关性高（r=-0．73，P〈0．01），两种视力表视力差值不随视力水平的改变而变化（P=-0．60）。正常屈光状态下儿童Lea Symbols 平均视力0．16±0．07（120眼）。Tumbling E的平均视力0123±0.07（91眼）。结论Lea Symbols视力表和Tumbling E视力表是测量视力可靠且有效的方法．检查4周岁以下儿童的视力时首选Lea Symbol视力表。与Tumbling E视力表相比，Lea Symbol视力表过高估计视力．原因可能在于两种视力表的不同设计以及儿童的认知水平差异。     

三种视力表视力测量差异研究

目的:探讨mc-3投影式视力表(A)、普通箱式视力表(B)以及综合验光仪(C)对不同年龄段人的裸眼视力及校正视力的测量结果是否有差异.方法:志愿者206人(395眼),根据患者年龄分为3组:青年组:25～45岁,共116眼;中年组:46～70岁,共102眼;老年组:71～90岁,共177眼.用视力表投影仪、普通箱式视力表以及综合验光仪分别测量各志愿者的裸眼视力及矫正视力.结果:矫正视力:3组中均无差别.裸眼视力:青年组、中年组中无差别.老年组中综合验光仪的视力测量结果要好于视力表投影仪和视力了表箱,差别具有显著性意义(秩和检验P＜0.05).结论:在老年组的裸眼视力测量结果中,综合验光仪好于视力表投影仪和视力表箱,这种视力测量的差异可能足由于不同背景亮度及视标照度下视标的对比度不同所引起.     

The effect of pupil size on visual acuity in uncorrected and corrected myopia.

The effect of pupil size on the relation between Snellen visual acuity and corrected and uncorrected myopia was examined for 22 young subjects with degrees of myopia ranging from 0.75 D to 7.5 D. Effective pupil size was varied by inducing mydriasis and then placing artificial pupils of between 1.0 and 8.0 mm diameter before the eye. Both a constant chart luminance of 120 cd/m2 and a constant retinal illuminance of 2150 trolands were used. There was little difference in results for the two lighting conditions. For the corrected myopes considered as a group, maximum visual acuity occurred for 2--3 mm diameter pupils, but larger pupils reduced acuity only marginally. For the uncorrected myopes, variation in pupil size produced a large variation in visual acuity, and for refractive errors greater than about 1.5 D, the optimum pupil diameter was less than 1 mm. For uncorrected myopes of 3.0 D or less, visual acuity was nearly as good with a 1-mm pupil as for corrected myopes. The presented data are a useful guide to the clinician.     

Letter contrast sensitivity in retinitis pigmentosa patients assessed by Regan charts

Regan Contrast Sensitivity Letter Charts were used to assess the effects of reduced contrast and luminance on visual acuity in retinitis pigmentosa (RP) patients. Letter acuity was measured monocularly in 17 RP patients and in 14 age-similar normals using charts of three different contrast levels presented at each of four levels of illumination. Despite visual acuities of 20/40 or better under standard clinical test conditions, an appreciable number of RP patients were unable to identify any letters on the intermediate- and/or low-contrast Regan charts. For example, even at the recommended test luminance, 5 patients could not read any letters on the intermediate (11%) contrast chart, and 9 could not be scored on the low (4%) contrast chart. Consequently, the Regan charts were found to have limited usefulness in quantifying the exact extent of visual impairment in this group of RP patients. Nevertheless, our results document the degree of visual acuity loss that can be experienced by RP patients under conditions of low contrast and luminance.     

Visual acuity changes with age: some new perspectives

Snellen chart visual acuity is thought to change very little up to age 60 years. However, any changes in contrast in the retinal and/or neural image with age may only be detected in low contrast and low luminance testing conditions. Only under these conditions does contrast significantly influence visual acuity measurements. In this pilot experiment we show that low contrast visual acuity is considerably worse (two lines of Snellen acuity) for an older group (N = 8, mean age 57) than for a younger group (N = 9, mean age 24.6) in spite of the fact that each subject was referred to the study with 6/6 (20/20) or better acuity. At conventional contrast and luminance levels there is no significant difference between the two groups. The results also suggest that a simple measurement of contrast sensitivity for a small spot of light may allow a contrast correction factor to account for both age and luminance level differences in the contrast vs. acuity function.     

A near-vision chart for children aged 3-5 years old:new designs and clinical applications

AIM:To introduce a new near-vision chart for children aged 3-5 years old and its clinical applications.METHODS:The new near-vision chart which combined the Bailey-Lovie layout with a newly devised set of symmetry symbols was designed based on Weber-Fechner law. It consists of 15 rows of symmetry symbols, corresponding to a visual acuity range from 1.3 to 0.1 logMAR. The optotypes were red against a white background and were specially shaped four basic geometric symbols:circle, square, triangle,and cross, which matched the preschool children's cognitive level. A regular geometric progression of the optotype sizes and distribution was employed to arrange in 15 lines. The progression rate of the optotype size between two lines was 1.2589 and two smaller groups of optotypes ranging from 0.7 to -0.1 logMAR were included for repetitive testing. A near visual acuity was recorded in logMAR or decimal, and the testing distance was 25 cm.RESULTS:This new near-vision chart with pediatric acuity test optotypes which consists of 4 different symbols (triangle, square, cross, and circle) met the national and international eye chart design guidelines. When performing the near visual acuity assessment in preschoolers (3-5 years old). It 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. Near vision may be recorded in different notations:decimal acuity and logMAR. These two notations can be easily converted each other in the new near-vision chart. The measurements of this new chart not only showed a significant correlation and a good consistency with the Chinese national standard logarithmic near-vision chart (r=0.932, P<0.01), but also indicated good test-retest reliability (89% of retest scores were within 0.1 logMAR units of the initial test score) and a high response rate.CONCLUSION:The results of this study support the validity and reliability of near visual acuity measurements using the new near-vision chart in children aged 3-5y over a wide range of visual acuities, and the new eye chart was especially suitable for the detection of amblyopia risk factors and low vision examination in children (3-5y of age). It can be applied in routine clinical practice.     

Comparison of visual acuity levels in pediatric patients with amblyopia using Wright figures, Allen optotypes, and Snellen letters.

PURPOSE: To compare and correlate the clinical performance of Wright figures in visual acuity assessments of pediatric patients with amblyopia to those obtained through Allen cards and Snellen letters. SUBJECTS AND METHODS: Best-corrected visual acuity of 26 amblyopic children were measured with the Wright figures(c), Snellen letters, and isolated Allen optotypes, respectively. Amblyopia was defined as two lines of visual acuity difference or a visual acuity level of 20/30 or lower as determined by Snellen chart. The results were evaluated for statistical intergroup differences using the Wilks' Lambda multivariate analysis of variance and for correlation using the Pearson correlation coefficient test. RESULTS: The mean age of the subjects was 8.27 +/- 2.46 years (range: 5 to 15 years). The mean logMAR values for the Wright figures(c), Snellen letters, and Allen optotypes were 0.40 +/- 0.20, 0.47 +/- 0.23, and 0.29 +/- 0.28, respectively. When compared with Snellen letters, the Wright figures correlated to a higher degree ( r = 0.46, P < 0.001) than Allen optotypes ( r = 0.67, P < 0.001). With a visual acuity of 20/40 or worse on Snellen letter testing, the sensitivity of Wright figures(c) and Allen cards in diagnosing amblyopic eyes was 87.0 and 56.5%, respectively ( P = 0.016). CONCLUSIONS: Wright figures, designed primarily to evaluate the vision in the preliterate pediatric population, correlate more closely to Snellen letters and have a higher rate of correctly identifying amblyopia than isolated Allen optotypes in pediatric patients.     

A new set of variable-contrast visual acuity charts

Using a computer plotting technique, we designed four variable-contrast visual acuity charts. The contrast of the first 3 is 90, 15, and 2.5%, respectively. The fourth is 90%, but the luminance of the optotypes and background are the reverse of the first chart. The main features of these charts are as follows. Both contrast sensitivity and spatial frequency are in geometric gradation, which observes the laws of Weber and Fechner. The mean average luminance, (Lmax + Lmin)/2, is constant for all four charts, which follows the concept of contrast sensitivity function (CSF). Charts 1 and 4, which have the same contrasts but different glare backgrounds, measure the glare that is related to the transparency of the refractive media of the eye. Because the charts are rotatable, patient memorization and guessing are minimized. Results compared with those of the conventional visual acuity test and are understandable by patients and eye care practitioners. The charts, which are simple, easy, and require little time, are inexpensive and portable.     

Visual acuity and its measurement

Despite its critical importance to our daily life, the most common measurement of visual function, visual acuity, is a relatively crude and narrow one testing only a small portion of the broad range of visual functions. Visual acuity is the measurement of the ability to discriminate two stimuli separated in space at high contrast relative to the background. Clinically, this is measured by asking the subject to discriminate letters of known visual angle. The visual acuity is represented as the reciprocal of the minimal angle of resolution (the smallest letters resolved) at a given distance and at high contrast. Other measurements of visual acuity also exist, including Vernier acuity. Newer charts, such as the ETDRS chart, use letters of equal recognition difficulty and use the log of the minimal angle of resolution; these charts have significant advantages over the old Snellen-type charts. This article reviews visual measurements in children and in patients with low vision, and it reviews factors affecting visual acuity, such as pupil size, refractive error, media opacities, and pharmacologic agents.     

Visual acuity results in school-aged children and adults: Lea Symbols chart versus Bailey-Lovie chart.

PURPOSE: To compare visual acuity results obtained using the Lea Symbols chart with visual acuity results obtained with the Bailey-Lovie chart in school-aged children and adults using a within-subjects comparison of monocular acuity results. METHODS: Subjects were 62 individuals between 4.5 and 60 years of age, recruited from patients seen in five optometry clinics. Each subject had acuity of the right eye and the left eye tested with the Lea Symbols chart and the Bailey-Lovie chart, with order of testing varied across subjects. Outcome measures were monocular logarithm of the minimum angle of resolution (logMAR) visual acuity and inter-eye acuity difference in logMAR units for each test. RESULTS: Correlation between acuity results obtained with the two charts was high. There was no difference in absolute inter-eye acuity difference measured with the two acuity charts. However, on average, Lea Symbols acuity scores were one logMAR line better than Bailey-Lovie acuity scores, and this difference increased with worse visual acuity. CONCLUSIONS: The Lea Symbols chart provides a measure of inter-eye difference that is similar to that obtained with the Bailey-Lovie chart. However, the monocular acuity results obtained with the Lea Symbols chart differ from those obtained with the Bailey-Lovie chart, and the difference is dependent on the individual's absolute level of visual acuity.     

Repeatability of an automated Landolt C test, compared with the early treatment of diabetic retinopathy study (ETDRS) chart testing

PURPOSE: To evaluate the repeatability of visual acuity scores from the automated test and compare them with the Early Treatment of Diabetic Retinopathy Study (ETDRS) chart. DESIGN: Instrument validation study based on a model of repeatability study in two observations. SMETHODS: a prospective, clinic-based, comparative study. A total of 206 participants without ocular diseases and refractive errors in their right eyes were randomly enrolled in the automated group in which 107 participants performed the automated test and the ETDRS group in which 99 participants read the ETDRS chart. All participants were tested with only their right eyes without corrections at 4 meters and came back to have the same tests 1 week later. The automated test used the Landolt rings as optotypes and was conducted by a low-ended personal computer with a 15-inch monitor and a wireless keyboard. The "letter" score calculated by counting every correct response to optotypes, and the "threshold curve" score interpreted from the optotype size at the midpoint of a visual acuity threshold curve. RESULTS: The 95% confidence interval of test-retest of visual acuity scores from the automated test are comparable to the ETDRS chart (.143 compared with.125 for letter scores,.145 compared with.122 for threshold curve scores). The score repeatabilities, calculated from the standard deviations of test-retest, from the automated test are also comparable to the ETDRS chart (.201 compared with.177 for letter scores,.206 compared with.172 for threshold curve scores). All comparisons demonstrated no statistical difference (P >.05). CONCLUSIONS: The automated testing system in this study enables practical measuring visual acuity by the Landolt rings. The system's repeatability, which is comparable to the ETDRS chart, supports its role as an alternative tool for measuring outcome in new clinical research. Its ability to practically generate visual acuity threshold curves may also be useful in future clinical research studies.     

Computeranimierte Kinderbilder zur Visusbestimmung

Background

Testing visual acuity is a very important element especially in the ophthalmological examination of children. The diagnosis and procedure of subsequent therapy depend on the results of vision testing. Some children achieve false low results in visual acuity because of reduced compliance. This can lead to incorrect diagnoses and false therapies.

Patients and methods

We developed a computer animated version of the visual acuity chart “Echelle Animaux”. This new test was first performed on 16 normal adult volunteers and then on 16 children who achieved as good visual scores in conventional tests as the control group. After that we tested 25 children with low compliance.

Results

Most of the tested children were more motivated and attentive when performing the new test. In 9 out of 25 children the measured visual acuity scores were clearly better than in the conventional test.

Conclusion

The animation of optotypes has a favourable effect on the motivation of children. The problem of reduced compliance and concentration can be reduced. The visual acuity scores can be improved by eliminating mistakes caused by low motivation.     

液晶视力表显示精度与显示屏点距的相关性分析

目的探讨液晶视力表测量精度与显示屏点距的关系。方法 采用标准对照研究方法,调查常用显示屏相关参数,与新标准对数视力表国家标准（GB11533-2011）的视标大小及允许误差进行推算、对比研究。结果 液晶视力表在亮度、幅宽、白度、照明方面完全符合（GB11533-2011）要求;在液晶显示精度方面,0.27 mm点距的显示屏可准确测试远视力≤5.0视力;0.1245 mm点距显示屏可准确测试远视力≤5.2视力;点距0.077 mm的显示屏准确测试远视力≤5.3视力。结论 选择合适点距和测试距离可使液晶视力表测试结果更精确。     

Contour interaction for foveal acuity targets at different luminances

Single-letter visual acuity is impaired by nearby flanking stimuli, a phenomenon known as contour interaction. We showed previously that when foveal acuity is degraded by a reduction of letter contrast, both the magnitude and angular spatial extent of foveal contour interaction remain unchanged. In this study, we asked whether contour interaction also remains unchanged when foveal visual acuity is degraded by a reduction of the target’s background luminance.Percent correct letter identification was measured for isolated, near-threshold black Sloan letters and for letters surrounded by 4 flanking bars in 10 normal observers, 5 at Anglia Ruskin University, UK (ARU) and 5 at Palacky University, Czech Republic (PU). A stepwise reduction in the background luminance over 3 log units resulted in an approximately threefold increase in the near-threshold letter size. At each background luminance, black flanking bars with a width equal to 1 letter stroke were presented at separations between approximately 0.45 and 4.5 min arc (ARU) or 0.32 and 3.2 min arc (PU).The results indicate that the angular extent of contour interaction remains unchanged at approximately 4 min arc at all background luminances. On the other hand, the magnitude of contour interaction decreases systematically as luminance is reduced, from approximately a 50% reduction to a 30% reduction in percent correct. The constant angular extent and decreasing magnitude of contour interaction with a reduction of background luminance suggest foveal contour interaction is mediated by luminance-dependent lateral inhibition within a fixed angular region.