Reliability of high- and low-contrast letter charts

Ophthalmic and Physiological Optics, 2004

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.

Clinical vision sciences, 1988

I. A consideration of methods for assessing contrast sensitivity leads to the conclusion that, for a clinical test, letters are more suitable than gratings. 2. A letter chart is described in which letters decrease in contrast but not in size. The letters are arranged in groups of three; successive groups decrease in contrast by a factor of IfJ2 from a very high contrast down to a contrast below the threshold of normal observers. A subject's threshold is taken to be the lowest contrast for which at least two letters in a group are correctly reported. 3. A mathematical model of the observer and the chart-testing procedure has been used to predict how the accuracy and repeatability of the test score depend on the parameters of the chart and observer. This reveals that even a low probability of misreporting supra threshold letters will seriously bias the test score if the passing criterion is strict, requiring correct report of all letters in each group, but will have little effect if the passing criterion is less strict. This effect of the passing criterion may explain Rubin's [Clin. Vision Sci. 2, No. I (1987)] finding that the new test, which uses a lenient criterion, has excellent test-retest reliability, much higher than the Ginsburg [Am. J. Optom. Physiol. Opt. 61,403-407 (1984)] chart with its strict criterion.

Vision Research, 2013

The need for precision in visual acuity assessment for low vision research led to the design of the Bailey-Lovie letter chart. This paper describes the decisions behind the design principles used and how the logarithmic progression of sizes led to the development of the logMAR designation of visual acuity and the improved sensitivity gained from letter-by-letter scoring. While the principles have since been adopted by most major clinical research studies and for use in most low vision clinics, use of charts of this design and application of letter-by-letter scoring are also important for the accurate assessment of visual acuity in any clinical setting. We discuss the test protocols that should be applied to visual acuity testing and the use of other tests for assessing profound low vision when the limits of visual acuity measurement by letter charts are reached.

Optometry and Vision Science, 2003

Snellen visual acuity was measured in 106 patients ranging in age from 20 to 88 years in routine examinations in the general refraction clinic with two kinds of charts: the standard chart using black letters on a white background and a reversed-contrast display featuring white letters on a black background. The overall ratio of the white-on-black to the black-on-white Snellen fractions was 1.043. A scattergram relating this ratio to patient age revealed that the older the patient, the more the visual acuity was improved by switching to the reversed-contrast chart, with a regression line slope of 0.5 ؎ 0.10. Impairment of the eye's optics, in particular by intraocular scatter causing a widening and flattening of the eye's point-spread function, explains these findings and suggests prognostic and therapeutic value of reversing the contrast polarity of displays.

Investigative Ophthalmology & Visual Science, 2006

PURPOSE: To compare the reliability, validity and responsiveness the Mars Letter Contrast Sensitivity (CS) Test to the Pelli-Robson CS Chart. METHODS: One eye of 47 normal control subjects, 27 open angle glaucoma patients, and 17 age-related macular degeneration (AMD) patients was tested twice with the Mars test and twice with the Pelli-Robson test, in random order, on separate days. Also, 17 patients undergoing cataract surgery were tested, once pre-surgery and once postsurgery. RESULTS: Mean Mars CS was 1.62 log CS (SD, 0.06 log CS) for normal subjects aged 22 to 77 years, with significantly lower values for glaucoma and AMD patients (P<0.001). Mars test-retest 95% limits of agreement (LOA) were 0.13, 0.19 and 0.24 log CS for normal, glaucoma and AMD subjects, respectively. In comparison, Pelli-Robson test-retest 95% LOA were 0.18, 0.19 and 0.33 log CS. The Spearman correlation between the Mars and Pelli-Robson tests was 0.83 (P<0.001). However, systematic differences were observed, particularly at the upper/normal end of the range, where Mars CS was less than Pelli-Robson CS. Following cataract surgery, Mars and Pelli-Robson effect size statistics were 0.92 and 0.88, respectively. CONCLUSIONS: The results indicate the Mars test has test-retest reliability equal to or better than the Pelli-Robson test and comparable responsiveness. The strong correlation between the tests provides evidence the Mars test is valid. However, systematic differences indicate normative values are likely to be different for each test.

British Journal of Ophthalmology, 2001

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 oVers 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.

Oman Journal of Ophthalmology, 2012

Background/Aim: Acuity charts that follow the principle of logarithmic size progression (logMAR charts) are considered to be the gold standard for the assessment of distant vision. But it is not well accepted for routine eye examinations due to increased testing time and the complexity of scoring. This study was designed to check whether a modified logMAR chart with three optotypes would provide a reliable acuity assessment compared to standard logMAR charts for routine eye examination. Materials and Methods: Two versions of modified and standard logMAR charts were designed, constructed, and used to assess the visual acuity of 50 individuals drawn from a typical outpatient population. Timed test-retest variability and limit of agreement (95% confidence limit of agreement) of the modified chart are compared to the standard logMAR chart using Bland-Altman method. A comparison of the testing time was carried out using paired t-test. Results: The test-retest variability of the charts was comparable, with 95% confidence limit of the mean difference being ±0.08 for standard logMAR and ±0.10 for modified logMAR. Both the versions of modified logMAR charts produced the results which agreed well with those of the standard logMAR charts. The mean testing time required to complete the acuity measurements with the modified chart was significantly lesser compared to the standard chart (P < 0.001). Conclusion: The outcomes of the current study demonstrates that the modified logMAR chart with three optotypes offers a comparable result to the standard logMAR charts for assessing distant visual acuity in routine clinical examination set up with a much lesser testing time.

In this study the visual performance of aviators and a myopic, non-aviator group were compared to determine the effects of aging, available light and refractive error. The chart used is a novel chart called the Small Letter Contrast Test (SLCT) which measures sensitivity to contrast at the moderate to high end of the spatial frequency range near the visual acuity thresholds of most normal observers. All three variables influence visual performance on the SLCT, age having a greater effect on low luminance performance and refractive error having comparable effects on SLCT performance regardless of luminance level. High contrast visual acuity remains fairly stable and normal over the age range tested; however it decreases with increasing refractive error.

Purpose: Contrast sensitivity (CS) testing using chart tests of CS is becoming increasingly common in low vision assessment. Yet we know little about the validity of these charts, i.e. which region of the spatial frequency spectrum is being measured. In this study we aimed to determine the validity of currently available CS charts by comparison against osciUo scope-based CS. We also determined their relative ability to predict reading speed.

Investigative Ophthalmology Amp Visual Science, 1997

Purpose. To design and evaluate a new vision test that combines low contrast and reduced illumination to stress the visual system and be sensitive to subtle alterations in function. Methods. A simple new clinical test, the Smith-Kettlewell Institute Low Luminance (SKILL) Card, is designed to measure spatial vision under conditions of reduced contrast and luminance using normal office lighting. The SKILL Card consists of two near acuity charts mounted back to back. One side has a chart with black letters on a dark gray background designed to simulate reduced contrast and luminance conditions. The other side has a high-contrast, black-on-white letter chart. The SKILL score is the acuity loss (number of letters) between the light and dark sides. Results. Age norms for a large normal population have been established and show that test scores increase with age, particularly after age 50. Repeatability is as good as that of standard Snellen acuity. The SKILL score is affected minimally by blur, but it is affected by large variations in light level. SKILL scores are sensitive to the presence of visual disease such as "recovered" optic neuritis. Conclusions. The SKILL card allows quick, reliable measurement of the effect of reduced luminance and contrast on acuity. SKILL scores are not correlated with other vision measures in patients with optic neuritis, which shows that the SKILL card measures a different dimension of vision function than existing clinical tests. Invest Ophthalmol Vis Sci. 1997;38:207-218. J. he Smith-Kettlewell Institute Low Luminance (SKILL) Card was developed to provide a simple, rapid, and inexpensive method for measuring vision function at reduced contrast and luminance. The combination of low contrast and reduced luminance is expected to increase sensitivity to vision changes caused by age and disease compared to standard highand low-contrast acuity measures and simulates conditions under which people most often report real-world task performance problems. The familiar black-on-white letter chart, originally