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.     

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.     

Visual acuity with reversed-contrast charts: II. Clinical investigation.

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.     

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.     

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.     

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.     

Effects of dioptric blur on Snellen and grating acuity

We compared the effects of dioptric blur on Snellen acuity and grating acuity. Dioptric blur had a strong negative effect on Snellen acuity, consistent with previous studies, but had little effect on grating acuity. Between 1 and 12 D both types of acuity were reduced as a linear function of blur. However, 12 D of blur reduced grating acuity to only 6/24 (20/80), whereas letter acuity was worse than 6/300 (20/1000). We suggest that these differences are due to the presence of "spurious resolution" in which phase-reversed gratings are readily detectable. But the phase reversals so distort the relative positions of linear segments within the letters that the letters become unrecognizable. These results indicate that Snellen letters are more sensitive than gratings to a patient's refractive errors, emphasize the differences between Snellen and grating acuity, and indicate that the minimum angle of resolution (MAR) concept is not applicable to letters.     

Glasgow Acuity Cards: a new test for the measurement of letter acuity in children

Problems with design and format of the traditional Snellen chart have led to the development of alternative charts for the measurement of visual acuity in adults. However, advances in chart design for the measurement of visual acuity in pre-school children have not paralleled those used in adult test charts. Visual acuity can be measured in infants and very young children using behavioural and electro-physiological techniques but clinical measurement of letter acuity tends to commence when the child is old enough to interact and co-operate with the examiner. Charts which arc commercially available in the UK for measuring letter acuity in pre-school children (3–5 years old) either use single optotypes or are derivatives of the Snellen format. There is a need for a test of letter acuity for use with this young age group which is accurate, reliable and based upon sound and established design principles. Glasgow Acuity-Cards have been designed to include features that should allow change in letter acuity to be detected in pre-school children, especially those undergoing vision therapy training. The test is performed at 3 m and incorporates several design features which have been used previously in adult charts but are new to childrens' test charts. These include: linear progression of letter sizes using a log scale; letters of approximately equal legibility; equal number of letters per line; control of contour interaction; screening cards to determine initial level of acuity. The test is quick and easy to perform and should provide a means of detecting change in letter acuity, with increased confidence.     

Performance of video-displayed letter charts

A software package was developed for an Apple-II microcomputer to display Snellen letters as test charts for high speed measurement of visual acuity. With direct viewing of a 30 cm (12 inch) monitor, letter sizes can range from 6/100 to 6/6. This range can be extended by using a modified monitor to display reversed letters for indirect viewing, to increase the testing distance. To circumvent patient learning, random presentation order of different charts (recalled rapidly from diskette) can be used. The video charts were compared with a Bailey-Lovie (IogMAR) Snellen chart by duplicating the letter sizes and format. Acuities were on average one line less for the video chart compared to the wall chart.     

A Calculator for LogMAR Visual Acuity Measurements

A sliding-scale calculator is presented that indicates the conventional (6m) Snellen acuity fraction, given any logMAR chart standard viewing distance and the size of the smallest letters on that chart read correctly by a patient.     

First-order Wiener kernel visually evoked potentials obtained from multiple sclerosis patients

Visually evoked potentials (VEP) were measured in multiple sclerosis patients with five sizes of reversing check stimuli. The VEPs were obtained using random binary sequence triggered check reversals. The random binary sequence was cross-correlated with scalp potential responses to obtain the estimates of the linear response of the system.For each evaluation a series of five VEPs, one for each of five check sizes, was done. A correlation coefficient was calculated to evaluate check size versus amplitude of the major negative wave. A tabulation was made to compare Snellen chart visual acuity with these correlation coefficients. For the eyes with a Snellen acuity of 20/20, 63% of the VEP amplitudes increased as the check size was decreased with correlation coefficients of -0.6 to -1. For the eyes with a Snellen acuity of 20/70 or less the amplitude decreased with the check size decrease, showing a correlation coefficient of +0.6 to +1 in 45% of the evaluations. The check size giving the largest amplitude was also tabulated with respect to the visual acuity, but did not appear to have as strong a relationship to visual acuity.     

The component of gaze selection/control in the development of visual acuity in children

Visual acuity was tested for 180 eyes of 90 children in four age groups using three types of test charts. Subjects read the same 10 high-contrast letters in Snellen (line) format, as isolated-letter flash cards, and as repeat-letter flash cards. Group mean line and group mean isolated-letter acuity showed similar progressive improvements with age. A subgroup of 24 of 50 eyes of 4- to 5-year-olds (15 of 25 subjects) and 3 of 50 eyes of 6- to 7-year-old (2 of 25 subjects) had low Snellen acuity. Of this low-acuity subgroup of 27 eyes, 10 scored above average for their age group on the repeat-letter chart. We concluded that abnormal lateral interactions were not the explanation for the immaturity of Snellen acuity in these 10 eyes. We suggest that an important factor in the low acuities of these 10 eyes is delayed development of the selection and/or control of gaze direction. Some eyes with excellent Snellen acuity showed high crowding. For example, there were five such eyes in the oldest group. We suggest that the excellent acuities of at least two of these eyes are limited by minor inaccuracies in gaze selection and/or control rather than by lateral interaction.     

Effects of luminance and contrast on visual acuity, ages 16 to 90 years.

Visual acuity of persons aged 16 to 90 years was measured with Snellen letters of varied contrast at 10, 1, 0.1, and 0.01 fl chart luminances. Percentage losses of seeing with age were computed. At 10 fl luminance, perception of high- and medium-contrast letters has changed little at age 40, but about twice as much light is needed to see low-contrast letters as at age 20. By age 70, no 2-min-subtense (20/40) letters were seen at 0.01 fl luminance. The need of older people for increased lighting during indoor tasks and night driving is discussed.     

First clinical experience with anecortave acetate (Retaane)

BACKGROUND: Anecortave acetate is an angiostatic cortisene which is injected as a posterior juxtascleral depot and has been shown to be effective in the treatment of exudative age-related macular degeneration (AMD). The compound is not yet approved in Switzerland but can be used as "compassionate use" in individual cases. PATIENTS AND METHODS: An uncontrolled case series with standardised documentation of ETDRS visual acuity, near acuity, need for magnification and fluorescein angiography was performed. RESULTS: 22 eyes of 19 patients (8 male, 11 female, average age 78.8 years) were treated with a posterior juxtascleral depot injection (PJD) of 15 mg anecortave acetate. The mean change in visual acuity after 3 months in eyes treated with anecortave acetate was -2.6 ETDRS letters corresponding to 0.52 Snellen lines. 3/20 eyes gained more than 1 line. 11/20 eyes showed stable visual acuity (+/- 1 Snellen line, +/- 5 ETDRS letters). 5/20 eyes developed moderate vision loss (one to two Snellen lines, 6-10 ETDRS letters). 1/20 lost 18 ETDRS letters (> 3 Snellen lines). There were no moderate or severe adverse events. CONCLUSIONS: A PJD of 15 mg anecortave acetate is safe and well tolerated. In eyes with occult CNV without recent progression or with residual neovascular activity after photodynamic therapy anecortave acetate may be an alternative therapeutic option before considering intravitreal anti-VEGF agents due to the much less invasive character and lower risk profile.     

The TRUE-VISTA bifocal IOL. Results of the European multicenter study]

In the last few years a number of bifocal IOL has been developed. The True Vista IOL, a three-zone refractive bifocal IOL with central and peripheral distance zones and a pericentral near annulus, was implanted in 367 patients in a prospective European multicenter study between February 1990 and May 1991. Visual acuity, pupil size and astigmatism were determined. At 4-6 months near acuity was measured with reading charts (Nieden Chart) and at 7-11 months with a Snellen chart (Lighthouse Chart). At 4-6 (7-11) months, so far 164 (73) of the patients have been available for follow-up. Best corrected distance acuity was 20/40 or better in 97% (99%), best corrected near acuity was 20/30 or better in 91% (83%), and uncorrected near acuity was 20/30 or better in 64% (59%). Average Snellen near acuity (Lighthouse Chart) was 20/25, slightly lower than the average reading acuity of 20/22 (Nieden Chart) (p = 0.34, Wilcoxontest). Distance and near acuity also decreased with increasing astigmatism and increasing age. Our results demonstrate good visual acuities with the True Vista bifocal IOL. Age and postoperative astigmatism may affect the performance of bifocal IOL. Snellen near acuity is reduced, despite normal reading acuity, but further investigation is required.     

Visual outcome in high hypermetropia.

INTRODUCTION: We wished to determine whether final visual acuity is dependent on age at optical correction or presence of esotropia in children with bilateral high hypermetropia. METHODS: We reviewed the charts of all patients at Childrens Hospital Los Angeles Division of Ophthalmology with bilateral hypermetropia of greater than or equal to 5D who were able to provide objective visual acuity outcomes with Snellen letters or linear E. RESULTS: One hundred thirteen patients met entry criteria. The age at first optical correction ranged from 8 months to 141 months (average 45 months). Initial visual acuity (before optical correction) was obtainable in 82 patients. Initial visual acuity ranged from 20/20 to 20/200, with 57% of patients having acuity better than or equal to 20/40. Final visual acuity (after optical correction) ranged from 20/20 to 20/70, with 109 patients (96%) having acuity better than or equal to 20/40 and 104 patients (92%) having acuity better than or equal to 20/30. There was no relationship between final visual acuity and age that spectacles were first worn. Ninety-five patients (84%) had esotropia with or without glasses, and six of these (6%) had final visual acuity less than 20/30. Of the 18 patients with orthotropia, three (16%) had final visual acuity less than 20/30. The prevalence of ametropic amblyopia in patients with esotropia and orthotropia was not significantly different (p = 0.18). CONCLUSION: Visual acuity outcome in children with high hypermetropia is generally good regardless of age at initial optical correction or presence of strabismus. A significantly increased risk for ametropic amblyopia was not found in those patients with orthotropia.     

Estimating visual acuity by character counting using the Snellen visual acuity chart

PURPOSE: This study examines visual acuity estimation with character counting, which can be used in subjects with nonorganic visual loss. METHODS: The right eyes of 35 healthy subjects were fogged with plus lenses and tested with the Snellen visual acuity chart (Reichert 11180). Visual acuity and counting level were assessed under various degrees of fogging, up to a maximal fogged acuity of 20/200. Counting level was defined as the smallest line that subjects could count the number of characters correctly. For each counting level, the visual acuity that 95% of subjects could see equal to or better than was determined. RESULTS: A counting level of 20/10 estimates (ie 95% chance) a visual acuity equal to or better than 20/30. Counting levels 20/15, 20/20, and 20/25 estimate visual acuities of at least 20/50, 20/80, and 20/80, respectively. Counting levels 20/30-20/60 estimate a visual acuity of at least 20/200. CONCLUSIONS: Character counting appears to be a useful technique of obtaining a rough estimate of visual acuity in subjects unable to be tested by standard methods, such as those with non-organic visual loss.     

Test charts for distance preferred for low-vision

Two wall test charts with Snellen letters on both sides have been designed for the purpose of testing vision accurately, especially for the patient with low vision. Visual designations of 20/160 (6/48) and 20/125 (6/37.5) are included on the chart. This makes each line 26% larger. Sloan letters are used and arranged so that each line is of equal difficulty.     

Relating vernier acuity and Snellen acuity in specific clinical populations

The relationship between vernier acuity and Snellen acuity in a group of cataract patients was examined. The vernier stimulus consisted of two small spots of light, vertically separated by a variable-sized gap. The Snellen stimulus was a standard projected Snellen chart. The form of the relation between vernier and Snellen acuity was found to depend upon the vernier gap size used. Specifically, when the smaller gaps of 4 or 8 min of arc are used, the two types of acuity are linearly related. When the gap is 16 or 32 min of arc, (or if best vernier performance irrespective of gap is considered) vernier acuity is related to Snellen acuity by a power function with an exponent less than one, within this clinical population. Thus, with increasing degrees of retinal image degradation caused by cataract, optimum vernier acuity is impaired at a slower rate than Snellen acuity. Our results in cataract patients are compared to results obtained by others within a population of strabismic and anisometropic amblyopes.     

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.