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Visual acuity and contrast sensitivity screening with a new iPad application

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Abstract

We present a new iPad application (app) for a fast assessment of Visual Acuity (VA) and Contrast Sensitivity (CS) and to evaluate reliability and agreement with a commercial screening device (Optec 6500). The measurement of VAs was programmed in the app in accordance with the Amblyopia Treatment Study protocol. The CS was measured with sinusoidal gratings of four different spatial frequencies: 3, 6, 12 and 18 cpd at the same contrast values of the Functional Acuity Contrast Test (FACT) included in the Optec 6500. Forty-five healthy subjects with monocular corrected visual acuities better than 0.2 logMAR participated in the agreement study. Bland-Altman analyses were performed to assess the agreement and Deming regressions to calculate Mean Differences (MDs) and Limits of Agreement (LoAs). Coefficients of reliability were 0.15 logMAR for our method and 0.17 logMAR for the EDTS testing protocol. For testing the CS our test has been completed in half the time compared with the FACT with no statistically significant differences between them, at any spatial frequency (p>0.05). The MDs were lower than 0.05 log units for all spatial frequencies.

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... The age of the participants in those studies varied significantly from 3 to 89 years. Five studies included children aged younger than 18 years [17,[19][20][21][22], 10 studies included middle-aged (19-55 years) adults [5,9,12,18,[23][24][25][26][27][28], and the remaining 7 studies included older adults (aged 55 years and older) [7,13,14,[29][30][31]. The main demographic characteristics of the participants in each study are summarized in Table S1 in Multimedia Appendix 2 and Multimedia Appendix 3. ...
... The 22 selected papers measured VA at a range from 36 centimeters to 6 meters: 8 studies measured VA at a 2-meter testing distance [13,14,19,20,29]; 3 studies measured VA at a 3-meter testing distance [9,21,26]; and the remaining 11 studies measured VA at 36 cm, 40 cm, 1 m, 1.2 m, 2 m, 14 inches, 20 feet, 4 m, and 6 m. Table 1 shows the characteristics and findings of 6 meta-analyses on mobile apps for VA testing. ...
... However, our analysis results showed lower specificity for children aged 3 to 5 years than the other 2 age groups. Previous literature has reported that the test of resolution acuity (eg, Tumbling E) may overestimate VA and thus be less sensitive for ocular diseases than tests of recognition acuity (eg, Lea, HOTV, Snellen) [26]. The American Association for Pediatric Ophthalmology and Strabismus Vision Screening app (ie, Lea symbols chart) was evaluated by Nik Azis et al [21] via an iPad mini in Malaysia among children aged 5 to 6 years. ...
... In the second analysis of the full text, 49 studies were excluded from the potentially eligible 68 articles (those previously selected). Table 1 summarizes the most relevant information of the articles finally included in the current article [2,6,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. A total of 49 articles were excluded from the review. ...
... As mentioned, one critical point of all these studies is that there is no mention or partial description of the visualization conditions present during the measurements (observation distance, screen tilt, ambience illumination level, and screen brightness) or the characterization (spatial and/or colorimetrical) of screens and the stimuli used in most of them. Only the studies from de Fez et al. [2] and Rodriguez-Vallejo et al. [25] mentioned that a previous characterization of the digital device used had been performed. Likewise, it is not clear that digital apps evaluating contrast sensitivity have considered that the concept of contrast should be based on luminance and not on a concept of the difference of digital levels. ...
... Rodríguez-Vallejo et al. [25] evaluated visual acuity and contrast sensitivity in 45 patients (Spanish adult university population) by employing a self-developed application that was previously validated [31]. These authors measured the chromaticity of an iPad with a retina display using the Spyder4Elite colorimeter and the luminosity of the room with theLX1330B luxmeter. ...
Article
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The current review aimed to collect and critically analyze the scientific peer-reviewed literature that is available about the use of digital applications for evaluation of visual parameters in electronic devices (tablets and smartphones), confirming if there are studies calibrating and validating each of these applications. Three bibliographic search engines (using the search equation described in the paper) and the Mendeley reference manager search engine were used to complete the analysis. Only articles written in English and that are evaluating the use of tests in healthy patients to measure or characterize any visual function aspects using tablets or smartphones were included. Articles using electronic visual tests to assess the results of surgical procedures or are conducted in pathological conditions were excluded. A total of 19 articles meeting these inclusion and exclusion criteria were finally analyzed. One critical point of all these studies is that there was no mention of the characterization (spatial and/or colorimetrical) of screens and the stimuli used in most of them. Only two studies described some level of calibration of the digital device before the beginning of the study. Most revised articles described non-controlled comparatives studies (73.7%), reporting some level of scientific evidence on the validation of tools, although more consistent studies are needed.
... Vision applications (apps) used to test lens performance were downloaded directly from the Apple App Store and included: VisionC® (2016) for the measurement of VA, Qvision® Multifocal Lens Analyzer (2017) for the measurement of VADC and ClinicCSF® (2017) for the measurement of CSF. These apps have been previously validated [26,27]. Only the right eye was assessed, due to the similar nature of both eyes. ...
... A + 0.50 D lens was placed on the trial frame in front of the right eye for the compensation of vergence. The app shows an Early Treatment Diabetic Retinopathy Study (ETDRS) VA chart of black optotypes placed over a white background [26]. VA was scored as the smallest optotype size at which the subject correctly identified 3 out of a maximum of 5 optotypes. ...
... Trial lenses from +1.50 D to -4.0D (in 0.50 D steps) were added over a compensatory distance lens of +0.50 D, which remained permanent throughout the procedure. The app shows a high-contrast Snellen-E optotype which changes its size (increasing or decreasing) in 0.1 logMAR steps, based on the subject's responses [26]. Eleven different VA results were acquired for each measurement, one for each defocus lens that made up the VADC. ...
Article
Purpose To determine the impact of different central optical zone diameters (COZDs), obtained from pupil size, on the visual performance of presbyopic subjects fitted with centre-distance simultaneous-image multifocal contact lenses (SIMCLs). Methods Thirty-two presbyopic volunteers, between 45–58 years of age, participated in this prospective, controlled, double-blind study. Subjects were fitted with 5 centre-distance SIMCLs of variable COZD, determined from the measurement of pupil size under photopic light conditions and corresponding to 60, 70, 80, 90 and 100 % of pupil diameter. Subjects visual performance was evaluated through the measurement of distance, intermediate and near visual acuity (VA), “visual functional range” (VFR) obtained from the VA Defocus Curve (VADC) and Contrast Sensitivity Function (CSF), using a third-generation retina display iPad. Results Statistically significant differences were obtained for both distance (p = 0.01) and intermediate (p = 0.001) VA amongst designs. Best results were obtained with 80 % and 90 % COZDs compared to 60 %. No significant differences in VFR (p > 0.05) were obtained amongst the different COZDs. 90 and 100 % COZDs offered statistically significant better results at 6 and 18 cycles per degree (cpd) in the CSF, compared to the 60 and 70 % designs. Conclusions SIMCLs with COZDs of 80–90 % and of 90–100% of photopic pupil diameter offered better distance and intermediate VA, without a decline in near performance, and superior contrast sensitivity at medium and high spatial frequencies respectively, compared to lower COZD designs.
... For this reason, low contrast VA tests [11], Contrast Sensitivity (CS) tests based on letters [12], and sinusoidal gratings [13] have been commonly used for assessing visual performance with MIOLs. CS is less repeatable than VA [14] and therefore requires complex psychophysical methods to obtain reliable measures, taking between 2 to 5 minutes per defocus point for the fastest reported procedures [14,15]. This means that for testing a CSDC with 11 defocus points, time spent would be around 22 and 55 minutes per eye. ...
... For this reason, low contrast VA tests [11], Contrast Sensitivity (CS) tests based on letters [12], and sinusoidal gratings [13] have been commonly used for assessing visual performance with MIOLs. CS is less repeatable than VA [14] and therefore requires complex psychophysical methods to obtain reliable measures, taking between 2 to 5 minutes per defocus point for the fastest reported procedures [14,15]. This means that for testing a CSDC with 11 defocus points, time spent would be around 22 and 55 minutes per eye. ...
... The procedure for obtaining the VA threshold with the ETDRS chart included the following steps [20]: 1) the subject read the first letter of the starting row and advanced one row with each right answer reading only one letter per row, 2) after the first mistake, the subject went to the previous row and read it completely, 3) advancing to the next row if the subject read 3/5 letters or went back to the previous if read less than 3/5; 4) the threshold was the last line for which the subject read 3/5 letters. For contrast sensitivity, the agreement at far distance with the Snellen E was evaluated versus a CSF test previously validated (ClinicCSF) [10,14], consisting of four sinusoidal gratings (3, 6, 12 and 18 cycles per degree, cpd) over a mean achromatic background brightness of 85 cd/m2 (Fig. 1C). Nine patches of different contrast levels were presented to the subject for each spatial frequency following a simple up-down staircase psychophysical method [17], starting in the fifth patch level for each spatial frequency. ...
Article
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Objective To evaluate the repeatability of the fast measurement of the visual acuity (VADC) and contrast sensitivity (CSDC) defocus curves with a new test as well as the agreement of measurements at far distance obtained with the Early Treatment Diabetic Retinopathy Study (ETDRS) chart and the ClinicCSF test for measuring Contrast Sensitivity Function (CSF). Method Records from fifty-nine subjects implanted with Multifocal Intraocular Lenses (MIOLs) were retrieved from our database. VADC and CSDC were measured from +1.00 D to -4.00 D in 0.50 D steps. The agreement with the ETDRS and the CSF at far distance was assessed in comparison to the 0 D location of the VADC and the CSDC, respectively. The repeatability was evaluated in 34 subjects who consecutively repeated two measures. Results Median Visual Acuity (VA) was -0.1 logMAR with the VADC at 0 D of defocus and 0 logMAR with the ETDRS (p>0.05). A total of 45.8% of eyes showed no differences between both tests and the difference was less than one line of VA in 96.6% of the eyes. The intrasubject repeatability was under one line of VA along all the defocus curve except for positive defocus levels. The CSDC showed the best agreement with the CSF for 18 cycles per degree. The CSDC was less repeatable than VADC. Mean time spent on completing the VADC and CSDC was 7.81 and 7.98 minutes, respectively. Conclusion The VADC showed good agreement with the ETDRS and good repeatability despite the short testing time. In contrast, poorer repeatability was found for CSDC. Our method would facilitate the inclusion of VADC in clinical practice as it is a fast test, being also the first one including the measure of CSDC.
... As stated, the default 8 Â 8 intra QM in HEVC is derived from a HVS-CSF based approach (Wang et al., 2001;Rodríguez-Vallejo et al., 2016). In the conventional technique, the HVS has demonstrated as a nonlinear point transformation charted by the Modulation Transfer Function (MTF) (Mannos and Sakrison, 1974). ...
... Rodríguez-Vallejo et al., 2016), the MTF is estimated using modified constant values e ¼ 2:2, g ¼ 0:192 , q ¼ 0:114 and r ¼ 1:1(Tech et al., 2016). The MTF is used to produce a 2D FWM, Wðk; lÞ , consisting of floating point values from which the threshold values of QM integer were derived. ...
Article
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As the concept of quantization matrix becomes an important feature in recent video CODECs, an optimized quantization matrix is being considered in the High-Efficiency Video Coding (HEVC) standard. This paper describes the entropy encoding by familiarizing optimized quantization matrix, and so higher rate of compression can be accomplished over the improved entropy encoding. Experiments show that for the eight benchmark video sequences and PSNR for varying rate of data transmission is explored. Comparative analysis is made with the improved (WE-Encoding) and standard entropy encoding based on the performance measurements. The simulation results show that the proposed method (WE-OQM) can save the originality of the decoded video sequence far better even though the compression rate is increased. In addition, the overall analysis states that the proposed method is 35.29% better than the Standard Encoding and 62.5% better than the WE-Encoding.
... Monocular uncorrected and corrected visual acuity and contrast sensitivity defocus curves (VADC and CSDC, respectively) were measured and plotted one and three months following IOL implantation, using the Multifocal Lens Analyzer 3.0 application designed for iPad devices (Qvision, Madrid, Spain; defocuscurve.com (accessed on 2 January 2022)) [27]. During the measurements and analysis, the recommendations and protocols provided by the developers were applied [28]. ...
Article
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The aim of our investigation was to examine the possible correlations between optical aberrations, angle kappa, angle alpha, and visual outcomes following cataract surgery. In total, 56 eyes of 28 patients were implanted with the Liberty 677MY trifocal intraocular lens (IOL). Pre- and postoperative higher-order aberrations, coma, astigmatism, angle alpha, and angle kappa were registered, along with uncorrected and corrected visual acuities at multiple distances. Visual acuity and contrast sensitivity defocus curves were plotted, and the areas under the curve were calculated 1 and 3 months postoperatively. Excellent visual outcomes were found at all distances. Patients reported low levels of dysphotopsia, and 96.4% of patients achieved complete spectacle independence. While angle kappa significantly decreased during cataract surgery (p = 0.0007), angle alpha remained unchanged (p = 0.5158). Angle alpha correlated with postoperative HOAs and had a negative impact on near vision (p = 0.0543). Preoperative corneal HOA and coma had a strong adverse effect on future intermediate and near vision. Residual astigmatism significantly affected postoperative intermediate vision (p = 0.0091). Our results suggest that angle kappa is not an optimal predictive factor for future visual outcomes, while angle alpha and the preoperative screening of optical aberrations might help patient selection prior to multifocal IOL implantation.
... This can be explained by the poorer repeatability of contrast sensitivity, which results in a higher bias in the model. 15,24 The higher variability of contrast sensitivity also explains why some authors found significant differences for visual acuity but not for contrast sensitivity, such as in corrections of spherical aberration. 25 It is important to note that the significance of a statistical test depends on the magnitude of the effect and on the variability; therefore for equal sample sizes, contrast sensitivity has lower statistical power and this can lead to a type II error, non-rejecting the null hypothesis when it is really true. ...
Article
Purpose: To evaluate whether the prediction of visual performance based on the modulation transfer function area (MTFa) calculated with optical simulations is better correlated with visual acuity or contrast sensitivity obtained from defocus curves in patients implanted with a trifocal intraocular lens. Methods: Biometric eye data from 43 patients were used to create a mean eye model. A trifocal intraocular lens with a power obtained from the mean of the eyes implanted was incorporated into the model and the MTFa was calculated at the 11 defocus planes corresponding the 11 defocus locations measured in clinical practice. Simulations were conducted for pupil diameters of 2.5, 3, 3.5, and 4 mm. The MTFa correlation with visual acuity and contrast sensitivity was evaluated with the mean obtained after stratification of the clinical sample in four groups according to the previous pupil diameters. Results: A linear model predicted the visual acuity and contrast sensitivity from MTFa with similar accuracy to nonlinear models, with R2 approximately 0.50 for visual acuity and approximately 0.42 for contrast sensitivity. A change of -0.01 logMAR and -0.02 logC was produced per unit of MTFa for visual acuity and contrast sensitivity, respectively. The mean difference between the visual acuity and contrast sensitivity obtained from the model and that measured in clinical practice was close to zero, but the bias varied depending on the defocus lens used, with higher deviation at -0.50 and -3.00 diopters of defocus. Conclusions: The MTFa obtained from optical simulations can be used to predict the mean visual acuity and contrast sensitivity consistently, with contrast sensitivity being more sensitive but with higher bias. [J Refract Surg. 2019;35(12):789-795.].
... At three months postoperatively, VADC and CSDC were measured under photopic vision conditions with the Multifocal Lens Analyzer (MLA) for iPad [7] . The MLA was designed and programmed by Rodríguez-Vallejo et al [8][9] in order to measure automatically VADC by means of a crowded Snellen E that changes its size in 0.1 logMAR steps and determining the threshold through a staircase procedure for each one of the defocus lenses, from +1.00 D to -4.00 D in 0.50 D steps. Furthermore, CSDC can be measured with the same optotype and procedure, but maintaining a specific optotype size and modifying its contrast in 0.1 log unit steps [10] . ...
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Citation: Fernández J, Rodríguez-Vallejo M, Martínez J, Tauste A, Piñero DP. Above-average defocus curves in photopic and mesopic vision with multifocal intraocular lenses after laser assisted in situ keratomileusis. Int J Ophthalmol (Oftalmar) and Vithas Virgen del Carmen (Qvision) hospitals in Spain. I write to describe a case in which the visual acuity defocus curves (VADC) and contrast sensitivity defocus curves (CSDC) in photopic and mesopic vision after the implantation of a multifocal diffractive trifocal intraocular lens (IOL) are above average values in normal eyes. We discuss potential causes for this unexpected positive outcome. Patients operated on with laser refractive surgery (LRS) in the past will develop with age presbyopia or age-related cataract. Possibly, these patients will desire to maintain their spectacle independence [1]. It is well known that LRS modifies the corneal shape and induces positive spherical aberration (SA) after myopic treatments and negative SA after hyperopic treatments [2]. For this reason, the use of some types of multifocal intraocular lenses (MIOLs) in such cases is controversial as these implants generate light scattering and deteriorate the optical quality of the eye. Indeed, poorer ocular optical quality is expected at far vision with MIOLs implanted in eyes with non-treated corneas compared to monofocal IOLs, with the potential of leading to some complaints, such as contrast sensitivity (CS) loss, glare, and halos [3]. Therefore, the visual performance with MIOLs may decrease even more after laser assisted in situ keratomileusis (LASIK), especially in mesopic conditions with low contrast tests [4]. However, the combination of the modified corneal shape after LRS and the specific optics of the MIOL may also generate an aberrometric compensation, allowing the patient to achieve visual acuities above 20/20 at far and near distances in mesopic conditions without a significant reduction of CS. A 48-year-old man that had been treated with LASIK five years ago for the correction of around 5 diopters (D) of myopia attended to our clinic seeking for surgical solution for his presbyopia. Refractive error was (-0.75) (-0.50) @80° in the right eye (RE) and (-1.75) (-0.50) @120° in the left eye (LE), with corrected distance visual acuity of-0.1 logMAR in both eyes. The near addition was +1.50 D. We used the Cataract Pre-op modulus of the Pentacam system (Oculus Optikgeräte, Wetzlar, Germany) for screening and IOL selection according to the four steps proposed by Maeda [5]. The corneal irregular Multifocal intraocular lens after refractive surgery Figure 1 Contrast sensitivity function measured under photopic and mesopic conditions with (CSPg and CSMg) and without glare (CSP and CSM) The grey area represents the range of normality defined for post-LASIK patients without MIOLs implanted.
... Then, the visual performance measurement was conducted with the selected lens. The visual performance of subjects fitted with MCLs was assessed by measuring: visual acuity (VA) ( Rodríguez-Vallejo et al. 2016), contrast sensitivity function (CSF) ( Rodríguez-Vallejo et al. 2015), stereopsis (ST) (Rodríguez-Vallejo M, Fajardo VC, Furlan WD, Pons A 2014), and through-focus response (TFR) ( Fernández et al. 2016) with Applications (APPs) developed for iPad Retina. All subjects were tested monocularly (with the exception of the stereopsis test) first, without compensation, and then, wearing the MCLs. ...
Article
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Objectives: To analyze the whole process involved in the production of a new bifocal Multizone Contact Lens (MCL) for presbyopia. Methods: The optical quality of a new MCL was evaluated by ray tracing software in a model eye with pupil different diameters with the lens centered and decentered. A stock of low addition (+1.5 D) MCL for presbyopia was ordered for manufacturing. Power profiles were measured with a contact lens power mapper, processed with a custom software and compared with the theoretical design. Nine lenses from the stock were fitted to presbyopic subjects and the visual performance was evaluated with new APPs for iPad Retina. Results: Numerical simulations showed that the trough the focus curve provided by MCL has an extended depth of focus. The optical quality was not dependent on pupil size and only decreased for lens decentered with a pupil diameter of 4.5 mm. The manufactured MCL showed a smoothed power profile with a less-defined zones. The bias between experimental and theoretical zone sizes was uniform along the optical zone unless for the most central area. Eyes fitted with the manufactured MCL showed an improvement in near Visual Acuity (VA) and near stereopsis. Althouh Contrast Sensitivity (CS) at distance decreased, the defocus curve for contrast showed an extended depth of focus correlated to the ray tracing results. Conclusions: The understanding of vision with MCL requires a process that involves design and characterization for detecting any defect that may have impact in the final visual performance. Keywords: Multifocal contact lenses, design, characterization, visual performance
Article
Background: Vision impairments (VIs) and blindness are major global public health issues. A visual acuity (VA) test is one of the most crucial standard psychophysical tests of visual function and has been widely used in a broad range of health care domains, especially in many clinical settings. In recent years, there has been increasing research on mobile app-based VA assessment designed to allow people to test their VA at any time and any location. Objective: The goal of the review was to assess the accuracy and reliability of using mobile VA measurement apps. Methods: We searched PubMed, Embase, Cochrane Library, and Google Scholar for relevant articles on mobile apps for VA assessment published between January 1, 2008, and July 1, 2020. Two researchers independently inspected and selected relevant studies. Eventually, we included 22 studies that assessed tablet or smartphone apps for VA measurement. We then analyzed sensitivity, specificity, and accuracy in the 6 papers we found through a meta-analysis. Results: Most of the 22 selected studies can be considered of high quality based on the Quality Assessment of Diagnostic Accuracy Studies-2. In a meta-analysis of 6 studies involving 24,284 participants, we categorized the studies based on the age groups of the study participants (ie, aged 3-5 years, aged 6-22 years, and aged 55 years and older), examiner (ie, professional and nonprofessional examiners), and the type of mobile devices (ie, smartphone, iPad). In the group aged 3 to 5 years, the pooled sensitivity for VA app tests versus clinical VA tests was 0.87 (95% CI 0.79-0.93; P=.39), and the pooled specificity was 0.78 (95% CI 0.70-0.85; P=.37). In the group aged 6 to 22 years, the pooled sensitivity for VA app tests versus clinical VA tests was 0.86 (95% CI 0.84-0.87; P<.001), and the pooled specificity for VA app tests versus clinical VA tests was 0.91 (95% CI 0.90-0.91; P=.27). In the group aged 55 years and older, the pooled sensitivity for VA app tests versus clinical VA tests was 0.85 (95% CI 0.55-0.98), and the pooled specificity for VA app tests versus clinical VA tests was 0.98 (95% CI 0.95-0.99). We found that the nonprofessional examiner group (AUC 0.93) had higher accuracy than the professional examiner group (AUC 0.87). In the iPad-based group, the pooled sensitivity for VA app tests versus clinical VA tests was 0.86, and the pooled specificity was 0.79. In the smartphone-based group, the pooled sensitivity for VA app tests versus clinical VA tests was 0.86 (P<.001), and the pooled specificity for VA app tests versus clinical VA tests was 0.91 (P<.001). Conclusions: In this study, we conducted a comprehensive review of the research on existing mobile apps for VA tests to investigate their diagnostic value and limitations. Evidence gained from this study suggests that mobile app-based VA tests can be useful for on-demand VI detection.
Article
Purpose: Recent innovations in mobile technology for the measurement of vision present a valuable opportunity to measure visual function in non-clinical settings, such as in the home and in field-based surveys. This study evaluated agreement between a tablet-based measurement of distance and near acuity and contrast sensitivity as compared to gold-standard clinical tests. Methods: Participants aged ≥55 years recruited from a tertiary eye clinic underwent testing with three tablet-based and corresponding gold-standard clinical measures (ETDRS distance acuity, Pelli-Robson contrast sensitivity, and MNRead near acuity). Correlation and agreement between tablet-based and clinical tests were assessed. Results: A total of 82 participants with a mean age of 69.1 (SD = 7.6) years, and majority female (67.1%) and white (64.6%), were enrolled in this study. The mean (SD) difference between the tests (gold-standard – tablet) was −0.04 (0.08) logMAR for distance acuity, −0.11 (0.13) log units for contrast sensitivity, and −0.09 (0.12) logMAR for near acuity. 95% limits of agreement for distance acuity (-0.21, 0.12 logMAR), near acuity (-0.34, 0.14 logMAR), and contrast sensitivity (-0.36, 0.14 logCS) were also determined. The correlation between tablet-based and gold-standard tests was strongest for distance acuity (r = 0.78), followed by contrast sensitivity (r = 0.75), and near acuity (r = 0.67). The agreement between the standard and tablet-based methods did not appear to be dependent on the level of vision. Conclusions: This study demonstrates the agreement of tablet-based and gold-standard tests of visual function in older adults. These findings have important implications for future population vision health surveillance and research.
Article
We present a new application for iPad for screening stereopsis at multiple distances that allows testing up to ten levels of stereoacuity at each distance. Our approach is based on a random dot stereogram viewable with anaglyph spectacles. Sixty-five subjects with no ocular diseases, wearing their habitual correction were measured at 3 m and 0.5 m. Results were compared with a standard stereoscopic test (TNO). We found not statistically significant differences between both tests, but our method achieved higher reproducibility. Applications in visual screening programs and to design and use of 3D displays, are suggested.
Thesis
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Myopia is the most prevalent refractive error from the age of 20 and impairs clear vision at far distance. Presbyopia, on the other hand, is an anomaly of the visual function that appears from the age of 45, impairs clear vision at near distance, and affects all people for being a natural age associated defect. Multifocal contact lenses represent a solution by which presbyopic patients can see simultaneously at multiple distances. Furthermore, they can be used, according to the last theories about optical signals that modulate the ocular growth, to slow down myopia progression in growing children. This Thesis proposes two new aperiodic contact lens designs for slowing down myopia progression or for presbyopia compensation. The first design has the main advantage of inducing greater relative peripheral refractive error with less impairment of central vision in comparison with the first lens commercialized in order to slow down myopia progression. This design has been manufactured, characterized, and the real efficiency has been measured in a sample of myopic subjects, offering a good agreement with its theoretical basis. The second design, for compensating presbyopia, has been also manufactured, characterized and tested in a sample of presbyopic subjects for measuring the visual performance achieved with the prototypes. Moreover, to accomplish this task, it was required to have a wide amount of different tests for testing vision at multiple distances. Therefore, another aim of this Thesis was to analyze the capabilities of the iPad for the reproduction of apps for measuring visual performance. New apps for measuring visual acuity, contrast sensitivity and stereopsis have been designed and validated for this purpose. With these new apps available, the visual performance was measured in the presbyopic subjects wearing the aperiodic contact lenses. Visual performance at near distance was significantly improved and the main advantage of the lens was the low pupil-dependence and good decentration tolerance despite of being a multizonal design.
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Technological advances have led to the development of powerful yet portable tablet computers whose touch-screen resolutions now permit the presentation of targets small enough to test the limits of normal visual acuity. Such devices have become ubiquitous in daily life and are moving into the clinical space. However, in order to produce clinically valid tests, it is important to identify the limits imposed by the screen characteristics, such as resolution, brightness uniformity, contrast linearity and the effect of viewing angle. Previously we have conducted such tests on the iPad 3. Here we extend our investigations to 2 other devices and outline a protocol for calibrating such screens, using standardised methods to measure the gamma function, warm up time, screen uniformity and the effects of viewing angle and screen reflections. We demonstrate that all three devices manifest typical gamma functions for voltage and luminance with warm up times of approximately 15 minutes. However, there were differences in homogeneity and reflectance among the displays. We suggest practical means to optimise quality of display for vision testing including screen calibration.
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An iPad-based letter contrast sensitivity test was developed (ridgevue.com) consisting of two letters on each page of an iBook. The contrast decreases from 80% (logCS = 0.1) to 0.5% (logCS = 2.3) by 0.1 log units per page. The test was compared to the Pelli-Robson Test and the Freiburg Acuity and Contrast Test. Twenty normally sighted subjects and 20 low-vision subjects were tested monocularly at 1 m using each test wearing their habitual correction. After a 5-minute break, subjects were retested with each test in reverse order. Two different letter charts were used for both the Pelli-Robson and iPad tests, and the order of testing was varied systematically. For the Freiburg test, the target was a variable contrast Landolt C presented at eight possible orientations and used a 30-trial Best PEST procedure. Repeatability and agreement were assessed by determining the 95% limits of agreement (LoA) ±1.96 SD of the differences between administrations or tests. All three tests showed good repeatability in terms of the 95% LoA: iPad = ±0.19, Pelli-Robson = ±0.19, and Freiburg = ±0.15. The iPad test showed good agreement with the Freiburg test with similar mean (±SD) logCS (iPad = 1.98 ± 0.11, Freiburg = 1.96 ± 0.06) and with narrow 95% LoA (±0.24), but the Pelli-Robson test gave significantly lower values (1.65 ± 0.04). Low-vision subjects had slightly poorer repeatability (iPad = ±0.24, Pelli-Robson = ±0.23, Freiburg = ±0.21). Agreement between the iPad and Freiburg tests was good (iPad = 1.45 ± 0.40, Freiburg = 1.54 ± 0.37), but the Pelli-Robson test gave significantly lower values (1.30 ± 0.30). The iPad test showed similar repeatability and may be a rapid and convenient alternative to some existing measures. The Pelli-Robson test gave lower values than the other tests.
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Purpose: Letter acuity, the predominant clinical assessment of vision, is relatively insensitive to slow vision loss caused by eye disease. While the contrast sensitivity function (CSF) has demonstrated the potential to monitor the slow progress of blinding eye diseases, current tests of CSF lack the reliability or ease-of-use to capture changes in vision timely. To improve the current state of home testing for vision, we have developed and validated a computerized adaptive test on a commercial tablet device (iPad) that provides an efficient and easy-to-use assessment of the CSF. Methods: We evaluated the reliability, accuracy, and flexibility of tablet-based CSF assessment. Repeated tablet-based assessments of the spatial CSF, obtained from four normally-sighted observers, which each took 3 to 5 minutes, were compared to measures obtained on CRT-based laboratory equipment; additional tablet-based measures were obtained from six subjects under three different luminance conditions. Results: A Bland-Altman analysis demonstrated that tablet-based assessment was reliable for estimating sensitivities at specific spatial frequencies (coefficient of repeatability 0.14-0.40 log units). The CRT- and tablet-based results demonstrated excellent agreement with absolute mean sensitivity differences <0.05 log units. The tablet-based test also reliably identified changes in contrast sensitivity due to different luminance conditions. Conclusions: We demonstrate that CSF assessment on a mobile device is indistinguishable from that obtained with specialized laboratory equipment. We also demonstrate better reliability than tests used currently for clinical trials of ophthalmic therapies, drugs, and devices.
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Summary-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.
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Visual acuity is a common measurement in general practice, and the advent of new technology such as tablet computers offers a change in the way in which these tests are delivered. The aim of this study was to assess whether measurements of distance visual acuity using LogMAR letter charts displayed on an iPad tablet computer were in agreement with standard clinical tests of visual acuity in adults with normal vision. Blinded, diagnostic test study. Single centre (University) in Auckland, New Zealand. University staff and students (n=85). Participants were required to have visual acuity better than 6/60 and wear habitual refractive correction during testing. Participants were excluded if there was any history of ocular pathology. Visual acuity measured under a number of conditions. The iPad tablet with its glossy screen was highly susceptible to glare resulting in acuity measurements that were significantly poorer (approximately 2 LogMAR lines) than those made using an ETDRS chart and a standard computerised testing system (n=56). However, fitting the iPad with an antiglare screen and positioning the device away from sources creating reflected (veiling) glare resulted in acuity measurements that were equivalent those made using gold standard charts (n=29). Tablet computers are an attractive option for visual acuity measurement due to portability, the ability to randomise letters, automated scoring of acuity and the ability to select from a range of charts. However, these devices are only suitable for use in situations where sources of glare can be eliminated.
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There are a multitude of applications using modern tablet computers for vision testing that are accessible to ophthalmology patients. While these may be of potential future benefit, they are often unsupported by scientific assessment. This report investigates the pertinent physical characteristics behind one of the most common highest specification tablet computers with regard to its capacity for vision testing. We demonstrate through plotting of a gamma curve that it is feasible to produce a precise programmable range of central luminance levels on the device, even with varying background luminance levels. It may not be possible to display very low levels of contrast, but carefully using the gamma curve information allows a reasonable range of contrast sensitivity to be tested. When the screen is first powered on, it may require up to 15 min for the luminance values to stabilize. Finally, luminance of objects varies towards the edge of the screen and when viewed at an angle. However, the resulting effective contrast of objects is less variable. Details of our assessments are important to developers, users and prescribers of tablet clinical vision tests. Without awareness of such findings, these tests may never reach satisfactory levels of clinical validity and reliability.
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The impression exists that picture acuity scores may overestimate function when subjects are switched to letter charts. This has not been systematically investigated. The aims of this study were to validate both printed crowded Kay picture (pCKP) and computerised CKP (cCKP) logMAR test acuity measurements against gold standard ETDRS letter chart scores. A total of 30 adult subjects with various ophthalmic disease and 40 amblyopic children underwent test and re-test visual acuity measurements using the ETDRS chart, the pCKP logMAR test, and the cCKP acuity scores taken, using the COMPlog visual acuity measurement system. Bland and Altman methods were employed. Computerised and printed Kay picture acuity scores agreed well. Both Kay picture test measurements were systematically biased when compared with ETDRS chart measurements. No significant proportional bias was found. The test retest variability (TRV) of all three tests was found to be similar between ± 0.14 and 0.16 logMAR in both groups. All three tests were similarly replicable and computerised Kay pictures appear to be a valid alternative to hard copy Kay pictures. Kay picture acuity measurements were systematically biased when compared with the gold standard ETDRS. Measurement error means that differences of up to 0.16 logMAR may be observed in clinically stable patients when re-measured using the same technique. A combination of TRV and systematic bias can however lead to differences of up to 0.40 logMAR in stable amblyopic patients when switched from CKPs to ETDRS chart acuity measurements.
Article
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The physical contrast of simple images such as sinusoidal gratings or a single patch of light on a uniform background is well defined and agrees with the perceived contrast, but this is not so for complex images. Most definitions assign a single contrast value to the whole image, but perceived contrast may vary greatly across the image. Human contrast sensitivity is a function of spatial frequency; therefore the spatial frequency content of an image should be considered in the definition of contrast. In this paper a definition of local band-limited contrast in images is proposed that assigns a contrast value to every point in the image as a function of the spatial frequency band. For each frequency band, the contrast is defined as the ratio of the bandpass-filtered image at the frequency to the low-pass image filtered to an octave below the same frequency (local luminance mean). This definition raises important implications regarding the perception of contrast in complex images and is helpful in understanding the effects of image-processing algorithms on the perceived contrast. A pyramidal image-contrast structure based on this definition is useful in simulating nonlinear, threshold characteristics of spatial vision in both normal observers and the visually impaired.
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Vision problems of preschool children are detectable with a comprehensive eye examination; however, it is estimated that only 14% of children below the age of 6 years receive an eye examination. Screening is advocated as a cost-effective alternative to identify children in need of further vision care. Thirty-four states recommend or require vision screening of preschool children. Although laws and guidelines exist, only 21% of preschool children are actually screened for vision problems. There is little agreement concerning the best screening methods, and no validated, highly effective model for screening vision of preschool children. Newer screening tests have been designed specifically for preschool populations, and can be administered by lay screeners. Many have not been validated. Several are recommended by states or organizations without convincing scientific evidence of their effectiveness. This paper summarizes current laws and guidelines for preschool vision screening in the United States, reviews advantages and disadvantages of several test procedures, and provides recommendations for developing future preschool vision screening programs.
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To investigate the repeatability and sensitivity of two commonly used sine wave patch charts for contrast sensitivity (CS) measurement in cataract and refractive surgery outcomes. The Vistech CS chart and its descendant, the Functional Acuity Contrast Test (FACT), were administered in three experiments: (1) Post-LASIK and age matched normal subjects; (2) Preoperative cataract surgery and age matched normal subjects; (3) Test-retest repeatability data in normal subjects. Contrast sensitivity was similar between post-LASIK and control groups and between the Vistech and FACT charts. The percentage of subjects one month post-LASIK achieving the maximum score across spatial frequencies (1.5, 3, 6, 12, 18 cycles per degree) were (50, 33, 13, 13, 0 respectively) for FACT, but only (0, 0, 13, 4, 0 respectively) for Vistech. A small number of cataract patients also registered the maximum score on the FACT, but up to 60% did not achieve the minimum score. Test-retest intraclass correlation coefficients varied from 0.28 to 0.64 for Vistech and 0.18 to 0.45 for FACT. Bland-Altman limits of agreement across spatial frequencies were between +/-0.30 and +/-0.85 logCS for Vistech, and +/-0.30 to +/-0.75 logCS for FACT. The Vistech was confirmed as providing poorly repeatable data. The FACT chart, likely because of a smaller step size, showed slightly better retest agreement. However, the reduced range of scores on the chart due to the smaller step size led to ceiling (post-LASIK) and floor (cataract) effects. These problems could mask subtle differences between groups of patients with near normal visual function as found post-refractive or cataract surgery. The Vistech and FACT CS charts are ill suited for refractive or cataract surgery outcomes research.
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To examine the optimal cutoff point for the use of the visual acuity test to screen for refractive errors in schoolchildren. In a sample of schoolchildren between 7 and 9 years old, visual acuity testing was performed using modified ETDRS charts monocularly without optical aids by trained personnel. Cycloplegic autorefraction was performed in each eye. The screening efficacy of using various cutoff points for referring children for further optometric/ ophthalmic assessment was studied. Myopia was defined as a spherical equivalent of at least -0.5 D, hyperopia a spherical equivalent of at least +2.0 D, and astigmatism a cylinder of at least -1.0 D in at least one eye. The sensitivity, specificity, and predictive values were calculated using each patient as a case; a receiver operator curve was plotted. A total of 1,028 children were tested. A satisfactory sensitivity/specificity profile was obtained using a referral criterion of visual acuity worse than or equal to 0.28 logarithm of the minimum angle of resolution in at least one eye. In this scenario, the sensitivity and specificity of this screening test were 72% (95% confidence interval [CI], 68 to 76) and 97% (95%CI, 95 to 98), respectively. The positive and negative predictive values were 96% (95%CI, 93 to 98) and 78% (95%CI, 75 to 82), respectively. The modified ETDRS visual acuity chart can be used to predict refractive errors in schoolchildren in Singapore in a sensitive and specific manner using a referral criterion of worse than or equal to 0.28 logarithm of the minimum angle of resolution.
Article
Objective To evaluate the reliability of a new visual acuity testing protocol for children using isolated surrounded HOTV optotypes.Methods After initial pilot testing and modification, the protocol was evaluated using the Baylor-Video Acuity Tester (BVAT) to present isolated surrounded HOTV optotypes. At 6 sites, the protocol was evaluated for testability in 178 children aged 2 to 7 years and for reliability in a subset of 88 children. Twenty-eight percent of the 178 children were classified as having amblyopia.Results Using the modified protocol, testability ranged from 24% in 2-year-olds to 96% in 5- to 7-year-olds. Test-retest reliability was high (r = 0.82), with 93% of retest scores within 0.1 logMAR unit of the initial test score. The 95% confidence interval for an acuity score was calculated to be the score ±0.125 logMAR unit. For a change between 2 acuity scores, the 95% confidence interval was the difference ±0.18 logMAR unit.Conclusions The visual acuity protocol had a high level of testability in 3- to 7-year-olds and excellent test-retest reliability. The protocol has been incorporated into the multicenter Amblyopia Treatment Study and has wide potential application for standardizing visual acuity testing in children.
Article
PurposeTo provide population-based normative visual acuity (VA) by age, in children participating in the Sydney Paediatric Eye Disease Study aged 6 to <72 months. Methods Monocular VA was measured using the Amblyopia Treatment Study (ATS HOTV) protocol (24 to <72 months). Some children were also tested using linear ETDRS or HOTV logMAR VA charts (30 to <72 months). If unable to perform recognition acuity, the Teller Acuity Cards II (TAC II) was performed (6 to <42 months). Children with significant refractive error or ocular disease were excluded. ResultsImprovement in VA with age was shown on all three vision tests (all p < 0.0001). Mean VA using ATS HOTV (n = 836) was 0.13 logMAR (6/8) at <36 months, which improved to −0.01 (6/6) at 66 to <72 months. Mean ETDRS/HOTV (n = 399) VA was 0.26 logMAR (6/11) at <36 months, which improved to 0.1 (6/7.5) at 66 to <72 months. Mean monocular TAC II (n = 442) was 5.7 cycles/degree (0.72 logMAR) at 6 to <9 months and improved to 12.4 cycles/degree (0.38 logMAR) at age 30 to <33 months. Associations with ATS HOTV VA included prematurity (p = 0.027) and socio economic status (SES) factors such as home ownership (p = 0.039) and employment of one (p = 0.019) or both parents (p = 0.003). ConclusionsVA norms in children improved with age and were different according to the VA test used. Low SES was associated with poorer VA, supporting the need for test specific VA norms to be established for different populations. The ATS HOTV appears to be the best test to use for vision screening due to its lower false positive referral rate.
Article
Visual discrimination tasks are commonly used to assess visual learning and memory in non-human animals. The current experiments explored the suitability of an iPad (Apple, Cupertino, California), as a low-cost alternative touchscreen for visual discrimination tasks. In Experiment 1, rats were trained with patterned black-and-white stimuli in a successive non-match to sample procedure. Rats successfully interacted with the iPad but failed to learn to withhold responding on trials in which the sample matched the comparison. Experiment 2 used the same patterned stimuli, but the procedure was simplified to a successive discrimination procedure and we explored the use of procedures known to facilitate discrimination learning. Rats that received training with differential outcomes and a differential reinforcement of other behavior schedule successfully acquired the task. In Experiment 3, the same rats were tested in a simultaneous discrimination task and we explored the use of a correction and non-correction method during acquisition. Rats that failed to learn the discrimination in the previous experiment, improved while trained with the correction method. These experiments support the use of the iPad in visual discrimination tasks and inform future studies investigating learning and memory within a touchscreen-equipped (iPad or other) apparatus.
Article
Method comparison studies are usually analyzed by computing limits of agreement. It is recommended that replicate measurements be taken by each method, but the resulting data are more cumbersome to analyze. We discuss the statistical model underlying the classical limits of agreement and extend it to the case with replicate measurements. As the required code to fit the models is non-trivial, we provide example computer code to fit the models, and show how to use the output to derive measures of repeatability and limits of agreement.
Article
Citation information: McAlinden C, Khadka J & Pesudovs K. Statistical methods for conducting agreement (comparison of clinical tests) and precision (repeatability or reproducibility) studies in optometry and ophthalmology. Ophthalmic Physiol Opt 2011, 31, 330–338. doi: 10.1111/j.1475-1313.2011.00851.x The ever-expanding choice of ocular metrology and imaging equipment has driven research into the validity of their measurements. Consequently, studies of the agreement between two instruments or clinical tests have proliferated in the ophthalmic literature. It is important that researchers apply the appropriate statistical tests in agreement studies. Correlation coefficients are hazardous and should be avoided. The ‘limits of agreement’ method originally proposed by Altman and Bland in 1983 is the statistical procedure of choice. Its step-by-step use and practical considerations in relation to optometry and ophthalmology are detailed in addition to sample size considerations and statistical approaches to precision (repeatability or reproducibility) estimates.
Article
Citation information: Armstrong RA, Davies LN, Dunne MCM & Gilmartin B. Statistical guidelines for clinical studies of human vision. Ophthalmic Physiol Opt 2011, 31, 123–136. doi: 10.1111/j.1475-1313.2010.00815.x Statistical analysis of data can be complex and different statisticians may disagree as to the correct approach leading to conflict between authors, editors, and reviewers. The objective of this article is to provide some statistical advice for contributors to optometric and ophthalmic journals, to provide advice specifically relevant to clinical studies of human vision, and to recommend statistical analyses that could be used in a variety of circumstances. In submitting an article, in which quantitative data are reported, authors should describe clearly the statistical procedures that they have used and to justify each stage of the analysis. This is especially important if more complex or ‘non-standard’ analyses have been carried out. The article begins with some general comments relating to data analysis concerning sample size and ‘power’, hypothesis testing, parametric and non-parametric variables, ‘bootstrap methods’, one and two-tail testing, and the Bonferroni correction. More specific advice is then given with reference to particular statistical procedures that can be used on a variety of types of data. Where relevant, examples of correct statistical practice are given with reference to recently published articles in the optometric and ophthalmic literature.
Article
To demonstrate differences in foveal contrast sensitivity (CS) between glaucomatous and nonglaucomatous eyes using a simple, rapid computerized test. This study included consecutive patients with glaucoma (35 eyes) and age-matched control participants (23 eyes) with visual acuity of 20/30 or better. Patients with any other ocular disease, including cataract, were excluded. All participants underwent a comprehensive ocular examination, perimetry, and CS. Contrast sensitivity was examined by means of 2 computerized psychophysical tests. The transient method included the presentation of a target in a temporal, 2-alternative, forced-choice procedure, and the static method involved 4 forced-choice procedures. The targets were Gabor patches with spatial frequencies of 1.5 to 9.0 cycles per degree. The tests were conducted under photopic and mesopic conditions. Significantly lower foveal CS was found in glaucomatous eyes under photopic and mesopic conditions for all spatial frequencies (P < .01). The transient and static methods yielded similar results and were significantly correlated (P < .001). All transient photopic and mesopic CSs were significantly correlated with cup to disc ratio (P < .05). The static photopic spatial frequency of 6 cycles per degree was significantly correlated with the severity of the glaucomatous damage. The results indicate that foveal CS is impaired in glaucoma despite good visual acuity, suggesting that central visual function damage occurs in glaucoma. The similarity between the 2 methods of testing implies that the static method, being the shorter and easier one, may be used in future research. Further research is necessary to establish a CS testing role in the screening and monitoring of glaucoma.
Article
The aim of this study was to analyze if differences exist between two available contrast sensitivity tests that use similar stimuli, specifically, the CSV-1000 (VectorVision, Greenville, OH)) and the VCTS-6500 (Vistech, Dayton, OH). Contrast sensitivity was measured on 105 healthy patients with ages ranged from 19 to 26 years with visual acuity of 20/25 or better. The tests were performed in the same room and contrast sensitivity was measured with the VCTS-6500 system and CSV-1000. For both tests, the spatial frequencies of 3, 6, 12 and 18 cycles per degree were recorded. Contrast sensitivity values were generally higher for the Vistech VCTS-6500 test being the difference statistically significant (p<0.001) for all the spatial frequencies. This difference was more significant for 3cpd spatial frequency and the two tests showed a better agreement for the 6cpd spatial frequency. Our results showed that there were significant differences between the VCTS-6500 and the CSV-1000 tests. Developments of some general recommendations or regulations in relation to clinical measurement of contrast sensitivity are necessary.
Article
The contrast sensitivity function (CSF) predicts functional vision better than acuity, but long testing times prevent its psychophysical assessment in clinical and practical applications. This study presents the quick CSF (qCSF) method, a Bayesian adaptive procedure that applies a strategy developed to estimate multiple parameters of the psychometric function (A. B. Cobo-Lewis, 1996; L. L. Kontsevich & C. W. Tyler, 1999). Before each trial, a one-step-ahead search finds the grating stimulus (defined by frequency and contrast) that maximizes the expected information gain (J. V. Kujala & T. J. Lukka, 2006; L. A. Lesmes et al., 2006), about four CSF parameters. By directly estimating CSF parameters, data collected at one spatial frequency improves sensitivity estimates across all frequencies. A psychophysical study validated that CSFs obtained with 100 qCSF trials ( approximately 10 min) exhibited good precision across spatial frequencies (SD < 2-3 dB) and excellent agreement with CSFs obtained independently (mean RMSE = 0.86 dB). To estimate the broad sensitivity metric provided by the area under the log CSF (AULCSF), only 25 trials were needed to achieve a coefficient of variation of 15-20%. The current study demonstrates the method's value for basic and clinical investigations. Further studies, applying the qCSF to measure wider ranges of normal and abnormal vision, will determine how its efficiency translates to clinical assessment.
Article
Method comparison studies are usually analyzed by computing limits of agreement (LoA). If only one measurement by each method is taken on each person, and the difference across the range is not constant, it has been suggested (Stat. Methods Med. Res. 1999; 8:136–160) to regress the differences on the averages and use the resulting equation to construct LoA. LoA can be converted to a prediction foumula for one method given a measurement by the other. The meaning of the regression of differences on means is clarified in the framework of a proper model and prediction equations linking one method to another are devised. The performance of this model based method is evaluated against the simple approach proposed earlier and against the Deming regression. Copyright
Article
Contrast sensitivity measurements were obtained from 64 patients with insulin-dependent (IDDM) and non-insulin-dependent (NIDDM) diabetes mellitus who had normal Snellen acuity and minimal or no visible diabetic retinopathy. Contrast thresholds were determined for stationary gratings at six spatial frequencies, ranging from 0.5 to 22.8 cycles/degree (c/deg), and for 1.0-c/deg gratings phase-alternated at 15 Hz. Data from each group of diabetic patients were compared with data from age-matched normal subjects. We found that (1) patients with IDDM and no retinopathy had normal contrast sensitivity, (2) patients with NIDDM and no retinopathy had abnormal contrast sensitivity at only one spatial frequency (22.8 c/deg), and (3) patients with NIDDM and background retinopathy had abnormal contrast sensitivity at all spatial frequencies tested. We also found a dissociation of Snellen acuity and contrast sensitivity, indicating that contrast sensitivity can be used as an early index of changes in the retina not demonstrated by measurements of visual acuity.
Article
To determine the relationship between changes in contrast sensitivity, if any, after glaucoma therapy and the test-retest reliability of the CSV-1000 contrast sensitivity test. Patients with primary open angle glaucoma (N = 16) were retrospectively evaluated to determine changes in visual function, as measured by contrast sensitivity, after beta-blocker therapy. A control group (N = 24) of normally sighted patients was tested and retested on contrast sensitivity. For the control group, the coefficients of repeatability (95% confidence interval for test-retest variability [COR]) were calculated for each spatial frequency. The CORs were compared to the changes in vision found after therapy in the patients with glaucoma. The group with glaucoma showed a significant improvement (P < .01) in contrast sensitivity at all spatial frequencies. The test-retest variance for normals, as measured by the COR, was smaller than the mean differences in contrast sensitivity before and after therapy at all spatial frequencies, expect 18 cyc/deg. Visual function in patients with glaucoma, as measured by contrast sensitivity, does improve after beta-blocker therapy. Further, the CSV-1000 is a clinically reliable tool for monitoring these changes.
Article
Large and small letter contrast sensitivity and visual acuity were assessed in 37 elderly eyes (mean VA -0.01 logMAR, Snellen 6/6) and their lens opacities were categorised and graded using the LOCS III system. Large letter contrast sensitivity was often not reduced in cataract from age-matched normal values and provided limited information. Small letter contrast sensitivity was shown to be a more sensitive measure of early cataract than visual acuity and large letter contrast sensitivity. Its usefulness may be limited by its strong correlation with visual acuity (r2 = 0.70), which is the standard and traditional measure of vision in cataract.
Article
Agreement between two methods of clinical measurement can be quantified using the differences between observations made using the two methods on the same subjects. The 95% limits of agreement, estimated by mean difference +/- 1.96 standard deviation of the differences, provide an interval within which 95% of differences between measurements by the two methods are expected to lie. We describe how graphical methods can be used to investigate the assumptions of the method and we also give confidence intervals. We extend the basic approach to data where there is a relationship between difference and magnitude, both with a simple logarithmic transformation approach and a new, more general, regression approach. We discuss the importance of the repeatability of each method separately and compare an estimate of this to the limits of agreement. We extend the limits of agreement approach to data with repeated measurements, proposing new estimates for equal numbers of replicates by each method on each subject, for unequal numbers of replicates, and for replicated data collected in pairs, where the underlying value of the quantity being measured is changing. Finally, we describe a nonparametric approach to comparing methods.
Article
To review the test characteristics and the quality of evidence regarding available screening tests for the detection of amblyopia in preschool-aged children to help primary care practitioners select a screening strategy. Systematic review of published studies. The MEDLINE database was searched from 1966 through January 1999 using a broad and inclusive strategy. A total of 9551 citations were identified. All studies that compared the results of commercially available screening tests in preschool-aged children to ophthalmologic examination. The setting of the study, the age of the population, the type of screening test, criteria for a positive screen, criteria for the ophthalmologic examination, test characteristics, and measures of reliability were abstracted by 2 reviewers for each selected study. Four eligible articles were identified that studied the test characteristics of 3 screening tests. None of these studies were performed in a primary care setting. Each study used different criteria for failure of the ophthalmologic examination. None of the studies measured observer or test reliability. Few high-quality data exist regarding the performance of preschool vision screening. Important future work should include the development of a consensus gold standard ophthalmologic examination and evaluation of screening tests in the primary care setting.
Article
To evaluate the reliability of a new visual acuity testing protocol for children using isolated surrounded HOTV optotypes. After initial pilot testing and modification, the protocol was evaluated using the Baylor-Video Acuity Tester (BVAT) to present isolated surrounded HOTV optotypes. At 6 sites, the protocol was evaluated for testability in 178 children aged 2 to 7 years and for reliability in a subset of 88 children. Twenty-eight percent of the 178 children were classified as having amblyopia. Using the modified protocol, testability ranged from 24% in 2-year-olds to 96% in 5- to 7-year-olds. Test-retest reliability was high (r = 0.82), with 93% of retest scores within 0.1 logMAR unit of the initial test score. The 95% confidence interval for an acuity score was calculated to be the score +/-0.125 logMAR unit. For a change between 2 acuity scores, the 95% confidence interval was the difference +/-0.18 logMAR unit. The visual acuity protocol had a high level of testability in 3- to 7-year-olds and excellent test-retest reliability. The protocol has been incorporated into the multicenter Amblyopia Treatment Study and has wide potential application for standardizing visual acuity testing in children.
Article
To evaluate the effects of perceptual learning on contrast-sensitivity function and visual acuity in adult observers with amblyopia, 23 anisometropic amblyopes with a mean age of 19.3 years were recruited and divided into three groups. Subjects in Group I were trained in grating detection in the amblyopic eye near pre-training cut-off spatial frequency. Group II received a training regimen of repeated contrast-sensitivity function measurements in the amblyopic eye. Group III received no training. We found that training substantially improved visual acuity and contrast-sensitivity functions in the amblyopic eyes of all the observers in Groups I and II, although no significant performance improvement was observed in Group III. For observers in Group I, performance improvements in the amblyopic eyes were broadly tuned in spatial frequency and generalized to the fellow eyes. The latter result was not found in Group II. In a few cases tested, improvements in visual acuity following training showed about 90% retention for at least 1 year. We concluded that the visual system of adult amblyopes might still retain substantial plasticity. Perceptual learning shows potential as a clinical tool for treating child and adult amblyopia.
Article
The purpose of this study was to evaluate three psychophysical tests for the measurement of contrast sensitivity (CS) and disability glare (DG) at different luminance levels. In 60 eyes of 60 individuals (group 1: 20 healthy eyes of young individuals; group 2: 20 healthy eyes of elderly subjects; group 3: 20 eyes with nuclear cataract), CS with best correction was measured twice with the Frankfurt-Freiburg Contrast and Acuity Test System (FF-CATS) and the Functional Acuity Contrast Test (FACT, 1.5 cycles per degree [cpd]) at 167 cd/m2 and 0.167 cd/m2, and with the Pelli-Robson Chart (PRC) at 100 cd/m2 with and without glare. Repeatability of test and retest, and discriminative ability between the different subgroups, were assessed for CS values. Maximum CS values varied across tests. In all groups, highest CS values were obtained with the photopic FF-CATS. For FACT scores at 1.5 cpd, there was a ceiling effect for young subjects. CS scores obtained with the PRC were the lowest. The PRC had the best test-retest repeatability of all tests. Under mesopic conditions with glare, reliability was generally lower; the FF-CATS had the highest repeatability of the mesopic tests. The FF-CATS discriminated best between the different groups for all conditions. There are large discrepancies in the test results between CS testing methods, especially under different lighting conditions. Results from different CS tests are not interchangeable.
Article
The validity and repeatability of visual acuity measures are particularly important in the detection and monitoring of childhood visual anomalies such as amblyopia. The repeatability and sensitivity of a new computerised visual acuity test, 'Staircased Procedure' is compared with the now gold standard visual acuity test, the early treatment of diabetic retinopathy study (ETDRS). Twenty-seven visually normal children (mean age: 6.7 +/- 1.1 years) and 27 children with amblyopia (mean age: 6.1 +/- 0.7 years) were tested with the ETDRS and Staircased Procedure. A retest was administered 4-5 weeks later and 30 min later for the visually normal and the amblyopic children, respectively. The staircased procedure produced significantly better visual acuity than the ETDRS for visually normal and amblyopic children. Repeatability was similar for both tests (ETDRS: 0.11 log units; staircased procedure: 0.13 log units). In conclusion, the Staircased Procedure was an acceptable test with high repeatability and validity.
Article
To compare two established visual acuity protocols: the Amblyopia Treatment Study HOTV (ATS HOTV) visual acuity protocol and the Electronic-Early Treatment of Diabetic Retinopathy Study (E-ETDRS) protocol, in children aged 5 to 12 years. Prospective cohort study. Crowded HOTV optotypes and crowded ETDRS optotypes were presented to 236 consecutive children aged 5 to 12 years using an electronic visual acuity tester (Palm handheld, personal computer, and monitor). Twenty-three percent of the children were classified as amblyopic, 35% as having uncorrected refractive error, 36% as normal, and 6% as other. Visual acuity test results were converted to logarithm of minimal angle of resolution (logMAR) units for analysis. In developmentally normal children (n = 230), testability was 100% for HOTV in 5- to 12-year-olds and 100% for E-ETDRS in 7- to 12-year-olds. The E-ETDRS testing could be completed in 52% of 5-year-olds and in 87% of 6-year-olds. Visual acuity performance was better when measured by HOTV compared with E-ETDRS (median difference 0.06 logMAR [three letters on a chart with five letters/line], P =.0001), and the difference was found in normal eyes, eyes with refractive error, and amblyopic eyes. The ATS HOTV protocol yields slightly better visual acuity performance compared with E-ETDRS in 5- to 12-year-olds, but on average by less than a logMAR level. This systematic difference is important when a physician changes testing modality as a child matures and should be considered when interpreting the results of recent and ongoing clinical trials in amblyopia.
Article
Measures of visual contrast sensitivity (VCS), rather than traditional measures of visual acuity using high-contrast stimuli, have been presented as better appraisals of visual dysfunction resulting from chemical exposures. The present study sought to determine if differences exist between two available measures of contrast sensitivity that use similar stimuli, specifically, a hand-held chart and an Optec 1000 vision tester. Monocular contrast sensitivity measures using both tests were obtained from 45 individuals as part of a NIOSH neurobehavioral test-battery appraisal. Test-retest reliability was found to be high for both the hand-held system and the Optec 1000 test (r=.750 and.773, respectively). In comparison to the automated test, the hand-held version produced statistically significant higher contrast sensitivity scores for lower spatial frequencies (1.5 and 3.0 cycles per degree) and lower scores for a relatively higher spatial frequency (18.0 cycles per degree [cpd]). Consequently, this study documents a difference in spatial frequency scores obtained with the hand-held form and Optec 1000 form of contrast sensitivity test, and attributes these differences to design characteristics affecting viewing. It is concluded that caution should be taken when making absolute comparisons of contrast sensitivity test scores between neurobehavioral studies that have used different forms of VCS testing.
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