Computer-based measurement of letter and word acuity

Determining causes of poor reading ability is an important step in trying to ameliorate reading performance in low-vision patients. One important parameter is word acuity. The principal aim of the current study is to develop a method to reliably measure acuities for isolated lowercase letters and words of differing length that can be used to test low-vision patients. Using isolated stimuli means that testing is relatively free of potential crowding and/or distracting attentional effects from surrounding words, it is unambiguous which stimulus subjects are trying to read and response times can be recorded for each stimulus. Across a series of experiments, subjects with normal vision were asked to read isolated lowercase single letters and lowercase words of 4, 7 and 10 letters, in separate tests. Acuities for uppercase Sloan letters were also measured to provide a reference, as they are commonly used to measure visual acuity. Each test was based upon the design principles and scoring procedures used in the Bailey-Lovie and ETDRS charts. Acuities for uppercase Sloan letters were found to be equivalent whether measured using ETDRS charts or the computer-based method. Measurement of acuities for lowercase single letters and lowercase words of 4, 7 and 10 letters had a reliability that was no worse than acuities for uppercase Sloan letters. Lowercase word acuities were essentially independent of word length. Acuities for single lowercase letters and lowercase words were slightly better than uppercase Sloan letters acuity. Optimal processing of lowercase single letters and 4-, 7- and 10-letter words occurred at character sizes that were at least 0.2-0.40 log MAR above acuity threshold, i.e. between 1.5 and 3 times threshold acuity for that particular stimulus. In general, critical character sizes appear similar across word lengths as progressive increases or decreases in these values were not observed as a function of the number of letters in the stimulus. We conclude that a computer-based method of stimulus presentation can be used to obtain highly repeatable measures of acuity for lowercase single letters and lowercase words in normal vision.     

An evaluation of the M&S technologies smart system II for visual acuity measurement in young visually-normal adults.

PURPOSE: To compare visual acuity measures obtained with the M&S Technologies Smart System II (SSII) and the revised Early Treatment of Diabetic Retinopathy Study (ETDRS) charts in terms of accuracy and test-retest repeatability. METHODS: Monocular visual acuities were taken in 57 young, visually normal adults on two separate visits in which both the SSII system and the ETDRS charts were tested in random order by two masked examiners. The eye to be tested throughout was chosen randomly at the initial visit. Measurements were made through an optimal phoropter correction, determined by a noncycloplegic refraction for a 10-foot distance. Both charts were presented at 10 feet, and were matched closely for luminance. RESULTS: The mean visual acuity in the group was -0.16 log minimum angle of resolution (MAR) for the ETDRS chart and -0.18 log MAR for the SSII, a small but statistically significant difference. A 95% confidence interval for the mean difference in visual acuity between the two charts was -0.033 log MAR to -0.003 log MAR. The test-retest repeatability was not significantly different in the two tests. The 95% limits of agreement for test-retest repeatability were -0.13 log MAR to +0.17 log MAR for the SSII and -0.12 log MAR to +0.13 log MAR for the ETDRS charts. CONCLUSIONS: The SSII can provide an accurate (mean difference<0.033 log MAR) and repeatable alternative to the ETDRS charts for visual acuity measurement in young, visually normal, well-corrected individuals.     

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.     

ETDRS对数视力表在儿童视力检查中的可重复性分析

目的：探讨ETDRS对数视力表对儿童视力检查的可重复性及其影响的相关因素。方法：在流行病学调查的过程中，随机使用ETDRS对数视力表，为250位裸眼视力低于0．5和98位视力正常儿童进行裸眼视力重复检查。结果：两次视力测量之间差异的均数为0．004log±0．07；Kappa分析结果具有很好的一致性（k=0．71）；性别与视力检查一致性无明显相关（P=0．845）；年龄与视力检查一致性有显著相关性（P=0．019），年龄越小视力检查一致性越差；屈光不正与视力检查一致性也有显著相关性（P=0．000），近视度数在-1．00D—-5．00D之间的儿童视力检查一致性相对差．而正视眼的视力检查一致性较好。结论：结果提示ETDRS对数视力表适合儿童视力检查，建议推广使用。眼科学报2008；24：48-52．     

Repeatability of the Waterloo Four-Contrast LogMAR Visual Acuity chart and Near Vision Test card on a group of normal young adults

PURPOSES: To investigate the repeatability of logMAR visual acuity (VA) with the Waterloo Four-Contrast LogMAR Visual Acuity (FCLVA) chart and the Near Vision Test (NVT) card. The differences and agreements between near logMAR VA using horizontally- and vertically-presented letters were also determined. METHODS: Visual acuity of one eye (55 subjects) was first assessed by using the FCLVA chart, comprising four charts of varying contrast, and then with the NVT card (comprising four charts of two contrasts and two presentations). Measurements were repeated after 3 or 4 weeks. RESULTS: No significant between-visit differences were observed for any of the charts used. The repeatability coefficient for the distance 90, 60, 30 and 10% charts were 0.07, 0.11, 0.15 and 0.16 log units, respectively. The repeatability coefficients of the near vision charts were 0.06, 0.04 (high contrast), 0.11 and 0.10 (low contrast) log units. The agreements between horizontally- and vertically-presented letters were good. The differences were similar to the repeatability coefficient of each chart. CONCLUSIONS: The repeatability coefficient of the high contrast distance and near chart was about half a line. Repeatability coefficients increase with decreasing contrasts for both distance and near charts, with coefficients of one line or more for low contrast charts. Variabilities in both distance and near VA increase with decrease in contrast. The presentation of the letters does not affect near VA and the agreement between horizontally- and vertically-presented letters (both high and low contrast) was within the repeatability coefficient of each chart.     

Repeatability of ETDRS visual acuity in children

PURPOSE: To evaluate repeatability of the best corrected log minimum angle of resolution (MAR) Early-Treatment Diabetic Retinopathy Study (ETDRS) acuity in a group of 6- to 11-year old children with myopia. METHODS: Best corrected monocular visual acuity (VA) of a subset of children (n = 86) enrolled in the Correction of Myopia Evaluation Trial (COMET; mean spherical equivalent refractive error -2.35 D with no more than 1.25 D astigmatism) was measured at baseline and 1 month later with ETDRS logMAR charts. Children started with logMAR 0.4 (6/15 or 20/50) and read each letter on all subsequent lines until they missed all letters in 1 line. RESULTS: At baseline, the mean best corrected logMAR VA was 0.003 +/- 0.076 (6/6 or 20/20 +/- 3.8 letters) in the right eye and 0.008 +/- 0.059 (6/6 or 20/20 +/- 2.95 letters) in the left eye. The signed difference between VA measured at baseline and that measured at 1 month was not significantly different from zero in either eye. Repeatability was not associated with age, but a small, statistically significant association with gender was detected in the left eye, with boys approximately 2 letters more variable than girls. The kappa statistic (agreement within 1 line) was good to excellent. CONCLUSIONS: Based on the 95% limits of agreement, the criterion for a statistically significant change in VA is no more than +/-0.15 logMAR (or +/-8 letters). This value is similar to those reported for adults and indicates that logMAR VA provides a repeatable measure of acuity in children.     

Normative Reference Ranges for Binocular Summation as a Function of Age for Low Contrast Letter Charts

Purpose: Binocular summation (BiS), defined as the superiority of binocular over monocular viewing on visual threshold tasks, is most often studied in laboratory settings. Few studies have evaluated BiS with readily available clinical tools. Low contrast acuity (LCA) charts are increasingly popular in clinical research, yet their utility in detecting BiS has not been evaluated.

Methods: 129 normal subjects aged 3 to 85 years were prospectively enrolled and underwent monocular and binocular testing using 2.5% and 1.25% Sloan LCA charts and Pelli-Robson (PR) contrast sensitivity (CS) charts at an academic institution. Subjects also underwent similar testing with Early Treatment Diabetic Retinopathy Study (ETDRS) VA charts. BiS was calculated as the difference between the better eye and binocular scores.

Results: Monocular and binocular scores decreased with increasing age for all metrics. The mean (±SD) BiS scores for 2.5% and 1.25% Sloan LCA were 6?±?4.5 and 3?±?5 letters, respectively. BiS score was 4.5?±?7 letters for PR charts and 2?±?3 letters for ETDRS VA. There was a significant effect of age on BiS for the low contrast metrics (P?≤?0.001 for all), but not for high-contrast ETDRS VA. Linear regression revealed significant associations between increased interocular difference (IOD) in acuity and decreased BiS for all tests, and associations between increasing age and decreased BiS for the LCA tests.

Conclusion: Of the clinical tests evaluated, 2.5% and 1.25% Sloan LCA charts most readily demonstrated BiS in young normal subjects. BiS declined with increasing age and increased IOD. Median values presented in this study may be useful for future clinical studies utilizing LCA.     

Modeling the effect of forward scatter and aberrations on visual acuity after endothelial keratoplasty

Purpose. To evaluate the effects on visual acuity of forward scatter and aberrations typical of those after Descemet stripping endothelial keratoplasty (DSEK). Methods. Twenty normal eyes of 20 subjects (ages 22-57 years) were examined with best spectacle correction. Under photopic conditions, high-contrast visual acuities (HCVAs) were measured by using ETDRS charts. Visual acuity was also measured by using aberrated charts that simulated the typical high-order aberrations at 12 months after DSEK. Forward scatter was induced by viewing the eye charts through a 1-mm-thick layer of scattering solution (Amco Clear, at a concentration of 4000 nephelometric turbidity units) and was measured with a straylight meter. Results. Forward scatter increased from 1.19 ± 0.11 log straylight parameter (log[s]; mean ± SD) without induced scatter to 1.57 ± 0.06 log(s) with induced scatter (P < 0.001). Induced scatter reduced HCVA on the nonaberrated chart by 2.7 Snellen letters, from 20/19 (Snellen equivalent) to 20/21 (P < 0.001) and by 2.1 letters on the aberrated chart, from 20/25 to 20/28 (P = 0.005). Addition of aberrations reduced HCVA by more than twice the number of Snellen letters than did induced scatter, by 6.4 letters with low scatter (P < 0.001), and by 5.8 letters with high scatter (P < 0.001). Conclusions. Under typical clinical testing conditions, increased forward scatter has minimal effect on visual acuity. High-order aberrations are a more likely cause of degraded visual acuity than is forward scatter in eyes with clear corneas after DSEK.     

Comparison of Snellen and Early Treatment Diabetic Retinopathy Study charts using a computer simulation

AIM: To compare accuracy, reproducibility and test duration for the Snellen and the Early Treatment Diabetic Retinopathy Study (ETDRS) charts, two main tools used to measure visual acuity (VA). METHODS: A computer simulation was programmed to run multiple virtual patients, each with a unique set of assigned parameters, including VA, false-positive and false-negative error values. For each virtual patient, assigned VA was randomly chosen along a continuous scale spanning the range between 1.0 to 0.0 logMAR units (equivalent to 20/200 to 20/20). Each of 30 000 virtual patients were run ten times on each of the two VA charts. RESULTS: Average test duration (expressed as the total number of characters presented during the test ±SD) was 12.6±11.1 and 31.2±14.7 characters, for the Snellen and ETDRS, respectively. Accuracy, defined as the absolute difference (± SD) between the assigned VA and the measured VA, expressed in logMAR units, was superior in the ETDRS charts: 0.12±0.14 and 0.08±0.08, for the Snellen and ETDRS charts, respectively. Reproducibility, expressed as test-retest variability, was superior in the ETDRS charts: 0.23±0.17 and 0.11±0.09 logMAR units, for the Snellen and ETDRS charts, respectively. CONCLUSION: A comparison of true (assigned) VA to measured VA, demonstrated, on average, better accuracy and reproducibility of the ETDRS chart, but at the penalty of significantly longer test duration. These differences were most pronounced in the low VA range. The reproducibility using a simulation approach is in line with reproducibility values found in several clinical studies.     

A comparison of visual acuity measured by ETDRS chart and Standard Logarithmic Visual Acuity chart among outpatients

AIM:To compare the results of visual acuity(VA)measured by Early Treatment Diabetic Retinopathy Study(ETDRS)chart,5 m Standard Logarithm Visual Acuity(5 SL)chart,and 2.5 m Standard Logarithm Visual Acuity(2.5 SL)chart in outpatients of age 12-80 y.METHODS:Each patient(totally 2000 outpatients)had both eyes tested with ETDRS chart at 4 m,5 SL chart at 5 m,and 2.5 SL chart at 2.5 m in random order.The VA values of outpatients were categorized by ages.VA values were expressed by log MAR recording method.RESULTS:The mean VA results of ETDRS charts,5 SL,and 2.5 SL chart were 0.52±0.28,0.50±0.30,and 0.46±0.28 log MAR,respectively.There was a statistically significant difference in the three eye charts in the whole group(P<0.001).For all subjects,the correlation of VA tested with three charts was statistically significant(Spearman correlation coefficient=0.944,0.937,0.946,all P<0.001).Bland–Altman analysis shows the 95%limits of agreement between the 5 SL and 2.5 SL chart were-0.182 to 0.210,-0.139 to 0.251,and-0.151 to 0.235 log MAR,respectively.CONCLUSION:The agreement between the three eye charts is not high.The VA measured by 5 SL chart is slightly better than that by ETDRS chart and 5 SL chart would be a suitable alternative when ETDRS chart are not available in the clinical situation.The VA measured by 2.5 SL chart is about 0.5 line better than VA tested with ETDRS chart,which may overestimate VA.     

ETDRS-fast: implementing psychophysical adaptive methods to standardized visual acuity measurement with ETDRS charts

PURPOSE. To measure visual acuity (VA) on Early Treatment Diabetic Retinopathy Study (ETDRS) charts with a modified faster procedure (ETDRS-Fast), based on adaptive psychophysics methods and to assess the method's validity and reproducibility. METHODS. Whereas the standard method for measuring VA with the ETDRS charts requires that the subject read all the letters beginning with the top row, in the ETDRS-Fast procedure, the subject is asked to read only one letter per row until a mistake is made. Then, following simple rules, the examiner finds a row from which the subject can begin reading all the letters downward, thus making the method identical with the standard method near threshold. VA determination was performed twice with both methods in 57 subjects in two separate sessions to assess validity and reproducibility. RESULTS. In both sessions the correlation between the two procedures was high (intraclass correlation coefficient 0.95), confirming the validity of the ETDRS-Fast procedure. Reproducibility was good for both procedures, with intraclass correlation coefficients of 0.94 for the standard and 0.96 for the ETDRS-Fast method. The ETDRS-Fast procedure allowed a significantly shorter test duration (-30%; P < 0.0001). CONCLUSIONS. Adaptive procedures allow accurate and fast determination of psychophysical thresholds by reducing the number of stimulus presentations when the subject is far from threshold. In the ETDRS-Fast method a few simple rules applied to optotype chart reading allow adaptation to each patient's level of VA. The ETDRS-Fast procedure significantly reduces test time and still yields results that are as accurate as those obtained with the standard method.     

The development of a "reduced logMAR" visual acuity chart for use in routine clinical practice

BACKGROUND/AIMS: The advantages of logMAR acuity data over the Snellen fraction are well known, and yet existing logMAR charts have not been adopted into routine ophthalmic clinical use. As this may be due in part to the time required for a logMAR measurement, this study was performed to determine whether an abbreviated logMAR chart design could combine the advantages of existing charts with a clinically acceptable measurement time. METHODS: The test-retest variability, agreement (with the gold standard), and time taken for "single letter" (interpolated) acuity measurements taken using three prototype "reduced logMAR" (RLM) charts and the Snellen chart were compared with those of the ETDRS chart which acted as the gold standard. The Snellen chart was also scored with the more familiar "line assignment" method. The subjects undergoing these measurements were drawn from a typical clinical outpatient population exhibiting a range of acuities. RESULTS: The RLM A prototype chart achieved a test-retest variability of +/-0.24 logMAR compared with +/-0.18 for the ETDRS chart. Test-retest variability for the Snellen chart was +/-0.24 logMAR using clinically prohibitive "single letter" scoring increasing to +/-0.33 with the more usual "line assignment" method. All charts produced acuity data which agreed well with those of the ETDRS chart. "Single letter" acuity measurements using the prototype RLM charts were completed in approximately half the time of those taken using the ETDRS and Snellen charts. The duration of a Snellen "line assignment" measurement was not evaluated. CONCLUSION: The RLM A chart offers an acceptable level of test-retest variability when compared with the gold standard ETDRS chart, while reducing the measurement time by half. Also, by allowing a faster, less variable acuity measurement than the Snellen chart, the RLM A chart can bring the benefits of logMAR acuity to routine clinical practice.     

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.     

Performance of a computerised visual acuity measurement device in subjects with age-related macular degeneration: comparison with gold standard ETDRS chart measurements

Purpose

The aim of the study was to compare the performance of two different COMPlog computerised, single letter scoring, visual acuity (VA) measurements against gold standard Early Treatment Diabetic Retinopathy Study (ETDRS) chart measurements in patients with age-related macular degeneration (AMD). One computerised algorithm presented five and the other presented three letters per line; both computerised algorithms utilised half, rather than the full-letter width spacing standard on ETDRS charts that might induce crowding, fixation problems, increased test–retest variability (TRV), and bias.

Methods

Fifty patients with AMD (mean age 83 years) underwent timed test and retest VA measurements using ETDRS charts and COMPlog five (C5) and three (C3) letters per line computerised VA measurement algorithms. All tests utilised single-letter scoring methodology. Bland and Altman methods were employed. Performance was measured in terms of bias, TRV, and test time.

Results

The C5 and C3 scores showed no bias compared with the ETDRS chart measurements. C5 measurements had equal TRV to the ETDRS chart (±0.13 logMAR) with similar median test times (105 and 96 s, respectively). C3 measurements were slightly more variable (TRV ±0.17 logMAR), but 30 s quicker than ETDRS chart measurements.

Conclusions

The closer letter spacing employed in COMPlog testing algorithms appears to have no adverse effect on VA measurements compared with the gold standard ETDRS chart in patients with AMD. The three letter per line testing algorithm facilitates faster testing but with a two letter increase in TRV.     

The slope of the psychometric function for Bailey-Lovie letter charts: defocus effects and implications for modeling letter-by-letter scores.

BACKGROUND: Visual acuity measurement often results in an imprecise endpoint because subjects correctly identify some but not all of the letters on one or more size levels on a letter chart. The extent of this transition zone from seeing to nonseeing can be described by probit size, which is calculated by performing Probit Analysis on letter chart data. There has been no previous research into the effects of optical defocus on letter chart probit size. METHODS: We tested 18 young visually normal subjects monocularly during three different defocus conditions: best spectacle correction (zero defocus) and +1.00 D and +2.00 D additions. Stimuli were Bailey-Lovie-style logarithm of the minimum angle of resolution (log MAR) letter charts constructed with a 0.05 logMAR size progression between size levels. Frequency of seeing data from these charts were used to calculate probit size. RESULTS: There were statistically significant effects of optical defocus on mean probit size. After Monte Carlo correction for bias, we believe that true mean values for probit size are about 0.07 logMAR for well-corrected subjects and up to 0.12 logMAR with optical defocus. CONCLUSION: The smaller probit size for well-corrected subjects should correspond to a sharper logMAR visual acuity endpoint and less intrasubject variability in logMAR acuity than for subjects with a larger probit size (optical defocus). Our modeling shows that these different probit sizes can also significantly affect letter-by-letter visual acuity scoring.     

Construction and validation of a Tamil logMAR chart

Purpose:  To design, construct and validate a new Tamil logMAR visual acuity chart based on current recommendations.
Methods:  Ten Tamil letters of equal legibility were identified experimentally and were used in the chart. Two charts, one internally illuminated and one externally illuminated, were constructed for testing at 4 m distance. The repeatability of the two charts was tested. For validation, the two charts were compared with a standard English logMAR chart (ETDRS).
Results:  When compared to the ETDRS chart, a difference of 0.06 ± 0.07 and 0.07 ± 0.07 logMAR was found for the internally and externally illuminated charts respectively. Limits of agreement between the internally illuminated Tamil logMAR chart and ETDRS chart were found to be (−0.08, 0.19), and (−0.07, 0.20) for the externally illuminated chart. The test – retest results showed a difference of 0.02 ± 0.04 and 0.02 ± 0.06 logMAR for the internally and externally illuminated charts respectively. Limits of agreement for repeated measurements for the internally illuminated Tamil logMAR chart were found to be (−0.06, 0.10), and (−0.10, 0.14) for the externally illuminated chart.
Conclusions:  The newly constructed Tamil logMAR charts have good repeatability. The difference in visual acuity scores between the newly constructed Tamil logMAR chart and the standard English logMAR chart was within acceptable limits. This new chart can be used for measuring visual acuity in the literate Tamil population.     

Measurement and analysis of visual acuity in multicenter randomized clinical trials in the United States: Findings from a survey

Purpose To describe visual acuity (VA) testing and scoring methods used in multicenter randomized clinical trials in ophthalmology in the United States (USA) sponsored by the National Eye Institute (NEI). Methods A survey was conducted among multicenter studies in the US that included one or more randomized clinical trials and were sponsored by the NEI, National Institutes of Health. To be included in the survey, a study had to have VA reported in one or more publications or patient eligibility based on VA, a majority of study subjects 13 years of age or older, and a patient population primarily or exclusively from the US. A standard survey form was completed for each study based on information presented in the study manual of procedures and publications. Findings were summarized and displayed with frequency distributions. Results The survey included 24 studies, each with enrollment initiated in the period 1972 to 1999.VA was one of the study eligibility criteria for 19 (79%) studies, and VA or change in VA was the primary outcome in 12 (50%) studies. ETDRS charts have been employed in 16 of 19 studies initiated after the charts were published in 1982. All studies but one specified in the documents reviewed that VA testing was performed at multiple VA test distances. For studies that used ETDRS charts, methods of converting VA scores obtained at different test distances to a common scale fell into two categories: 11 studies used a method similar in nature to that first reported in the Macular Photocoagulation Study, and 7 studies used a method similar in nature to that first reported in the Krypton-Argon Regression of Neovascularization Study. Conclusion The development of the ETDRS charts and a custom light box has led to more uniformity in VA test charts and chart illumination. However, details of VA measurement protocols vary widely from study to study. To assure comparable data across studies and ocular conditions, it would be useful to have a standard VA testing and scoring protocol with provisions for testing different levels of visual acuity that recommends a single method for converting scores from different test distances to a common scale and standard conversion of “off the chart”VA levels for calculation of means and changes in VA.     

Evaluating a new logMAR chart designed to improve visual acuity assessment in population-based surveys

AIMS: This study aimed to evaluate a new chart designed to improve the collection of visual acuity data in population-based surveys. The Reduced logMAR E chart (RLME) employs three letters per line, 'tumbling E' optotypes, and conforms to accepted contemporary design principles. METHODS: The performance of the chart was assessed within a population-based glaucoma survey in Thailand. Performance indices were test-retest variability (TRV) and agreement with acuity data measured using the ETDRS logMAR chart which acted as the 'gold standard'. RESULTS: The 95% confidence limits for TRV of RLME acuity data were +/-0.15 logMAR. This figure is consistent with published data on the TRV of acuities measured using five-letter-per-line logMAR charts. The mean difference between RLME and ETDRS acuity data was 0.00 logMAR (95% confidence intervals of +/-0.05 logMAR) indicating that RLME acuities agreed well with those of the ETDRS chart. The chart and its method of use was readily accepted by the local ancillary staff who required only minimal training before acuity measurement could be delegated to them. CONCLUSIONS: The study demonstrated that the RLME chart is capable of accurate and repeatable acuity measurements. Certain aspects of the design of the RLME chart may be particularly pertinent to the measurement of vision in population-based surveys.     

Effect of naturally occurring visual acuity differences between two eyes in stereoacuity

Stereoacuity was measured in 30 subjects with a naturally occurring visual acuity (VA) difference between the eyes. The stereoacuity was measured by a modified Howard's apparatus using the staircase method and VA was measured with log MAR charts. Stereoacuity was worse in subjects with a large VA difference between the two eyes; the correlation between stereoacuity and VA difference was significant ( r = 0.76, P < 0.001). Neither the VA of the worse eye nor of the better eye contributed to the reduction in stereoacuity. The deterioration was more obvious if VA difference between the two eyes was one line or more (correlation coefficient, r = 0.88, P < 0.001). This study also reinforces the use of a 70% stereo-threshold when attempt stereoacuity results to compare with other studies.     

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.