Repeatability of mesopic visual acuity measurements using high- and low-contrast ETDRS letter charts.

PURPOSE: To determine the repeatability of mesopic high-contrast (HC) and low-contrast (LC) visual acuity (VA) measurements made at distance and near in healthy young individuals. While the repeatability of photopic VA is well-known, there is a lack of information with regard to the repeatability of VA measured under low luminance conditions. METHODS: In two different sessions 1 week apart, best-corrected monocular VA was determined using HC (96 %) and LC (10 %) ETDRS charts under mesopic luminance conditions (0.75 cd/m(2)) at distance (HCD, LCD) and near (HCN, LCN) in 47 healthy subjects aged 22.9 ± 6.8 years. Repeatability was estimated by the Bland and Altman method, whereby the mean difference (MD) and the 95 % limits of agreement were determined as the coefficient of repeatability (COR). RESULTS: Mean logMAR VA values were HCD = 0.09, LCD = 0.44, HCN = 0.21, and LCN = 0.57. Mean differences in measurements between sessions 1 and 2 were not significant, and low in clinical terms (≤1 letter). Repeatability was better for the distance measurements at both high and lowcontrast (COR HCD ±0.11 and COR LCD ±0.11 logMAR vs COR HCN ±0.15 and COR LCN ±0.16 logMAR), and MDs were also slightly closer to zero for the distance measurements. Similar repeatability was observed between HC and LC VA, both at distance and near. CONCLUSIONS: In mesopic conditions, ETDRS charts offer repeatable best-corrected monocular VA measurements. The criterion for a significant change in logMAR VA was 1 line at distance and 1.5 lines at near.

Repeatability of the modified Thorington card used to measure far heterophoria.

PURPOSE: To determine the interexaminer and intraexaminer repeatability of the modified Thorington test (TH) for distance vision in young adults and to compare these results with those observed for the heterophoria tests most commonly used in clinical practice. Agreement among tests was also assessed. METHODS: Distance heterophoria was quantified on two separate occasions by two examiners in 110 subjects aged 18 to 32 years (mean, 19.74 years; SD, 2.5 years) using four different tests: cover test (CT) Von Graefe, Maddox rod, and modified TH. The repeatability of the tests and agreement between them was estimated by the Bland and Altman method whereby the mean difference and the 95% limits of agreement were determined as the coefficient of repeatability (COR) and coefficient of agreement. RESULTS: The Thorington test showed best interexaminer repeatability (COR = ±1.43Δ), followed closely by CT (COR = ±1.65Δ), whereas best intraexaminer repeatability was observed for CT (COR = ±1.28Δ) followed by TH (COR = ±1.51Δ). Among the different combinations of tests, TH and CT showed best agreement indicated by the lowest coefficient of agreement (±2.23Δ) and a low mean difference (-0.63Δ) between measurements. CONCLUSIONS: Good interexaminer and intraexaminer repeatability was observed for both TH and CT, and agreement between the two tests was also good. Given the simple administration of the TH, we recommend its clinical use to quantify distance horizontal heterophoria.

Intrasession repeatability and agreement of the anterior corneal assessment provided by a multidiagnostic device.

CLINICAL RELEVANCE: Multidiagnostic systems have recently appeared on the market. Knowledge of the repeatability and validity of any instrument is mandatory before its introduction in clinical practice. BACKGROUND: The aim of this work is to examine the intrasession repeatability of anterior pole measurements provided by the multidiagnostic device Wave Analyzer Medica 700 (WAM700) and agreement with Pentacam measurements in normal eyes. METHODS: In the right eyes of 113 participants, three repeat measurements of central keratometry, central corneal thickness, anterior chamber depth and corneal eccentricity were made with the WAM700 and Pentacam in random order. Intrasession repeatability and agreement were determined. RESULTS: Employing WAM700, intrasession repeatability for keratometry, central corneal thickness and anterior chamber depth was good (ICCs ≥ 0.992; CV 0.48-0.98%), yet worse than the values obtained for the Pentacam (ICCs ≥ 0.998; CV 0-0.33%). WAM700 showed excellent intrasession repeatability when used to measure the anterior chamber depth (Sw 0.03 mm). However, the repeatability of this device was inferior for central corneal thickness (Sw 4.24 µm) and keratometry measurements (Sw < 0.21 D) and was poor for corneal eccentricity (Sw 0.07; ICC 0.908; CV 14.58%). Agreement between WAM700 and Pentacam showed a high ICC for the keratometry measurements, central corneal thickness and anterior chamber depth (>0.972) but lower for corneal eccentricity (ICC 0.762). CONCLUSIONS: In healthy eyes, the WAM700 multidiagnostic device showed good intrasession repeatability for keratometry, central corneal thickness and anterior chamber depth measurements. Agreement between WAM700 and Pentacam was good for the anterior chamber depth measurement. However, these instruments cannot be considered interchangeable for keratometry, central corneal thickness and eccentricity readings.

Normal values for the size of a halo produced by a glare source.

PURPOSE: To determine the size of a halo in the visual field induced by bright light in healthy eyes of all ages using the Vision Monitor (MonCv3; Metrovision, Pérenchies, France) and to assess the repeatability of the method. METHODS: Measurements were made in the right eyes of 147 healthy subjects (mean age: 48.2 ± 16.2 years) who were classified into six age groups. Using the Vision Monitor, optotypes of low luminance were presented at a distance of 2.5 m. The visual angle subtended by the radius of the halo was calculated in minutes of arc (arc min). The repeatability of the method was determined in a subset of 37 subjects older than 50 years by calculating the Bland-Altman coefficient of repeatability. RESULTS: The mean radius of the halo was 111.6 ± 39.8 arc min. Halo radius started to increase significantly from the age of 50 to 59 years. The relationship between halo radius and age (r = 0.65; P < .0001) was described by fitting a power function to the data. Halo size was independent of gender. The coefficient of repeatability of the method was ±44 arc min. CONCLUSIONS: Halo size increases with age following a power model. The normal halo size values provided could help clinicians distinguish between normal or abnormal glare problems. The intersession repeatability observed for halo size measurement indicates this method could be useful for assessing visual impairment caused by glare.

Spanish Cross-Cultural Adaptation, Rasch Analysis and Validation of the Ocular Comfort Index (OCI) Questionnaire.

The Ocular Comfort Index (OCI) assesses ocular surface irritation and grades the severity of dry eye disease. This study sought to adapt the OCI questionnaire into Spanish, and then to assess the psychometric performance and validity of the new adapted version (OCI-versión española, OCIVE). The questionnaire was translated, back translated, and then cross-culturally adapted for use with Spanish-speaking individuals. The OCIVE was completed by 450 participants, including 53 subjects that were diagnosed with dry eye disease. Through a Rasch analysis, the psychometric properties of item fit, targeting, person separation, reliability, and differential item functioning (DIF) were assessed. To test the convergent validity, we examined the correlation between the OCIVE and the Computer Vision Symptom Scale (CVSS17). Validity was tested in a subgroup of participants with and without dry eye, and test-retest repeatability was determined in a subset of 151 individuals. We also compared, via DIF, the performance of the OCIVE with that of the original OCI. Our Rasch analysis revealed a good model fit, high accuracy, good targeting, unidimensionality, and no DIF according to gender. The validity and repeatability were good. The OCIVE shows comparable psychometric properties to the original English version, making it a valid tool for measuring dry eye symptoms in Spanish adults.

Spanish Cross-Cultural Adaptation and Rasch Analysis of the Convergence Insufficiency Symptom Survey (CISS).

Purpose: To culturally and linguistically adapt the Convergence Insufficiency Symptom Survey (CISS) to Spanish and assess the psychometric performance of the new version through Rasch analysis and classical test theory methods. Methods: The Spanish version of the CISS (CISSVE) was completed by 449 subjects (9-30 years old) from the general population. The validity and reliability of CISSVE were assessed through Rasch statistics (precision, targeting, item fit, unidimensionality, and differential item functioning). To test construct validity, we calculated the coefficients of correlation between the CISSVE and the Computer-Vision Symptom Scale (CVSS17) or Warwick-Edinburgh Mental Well-Being Scale (WEMWBS). We determined test-retest reliability in a subset of 229 subjects. We used differential item functioning (DIF) to compare the CISSSVE and the CISS after administering the CISS to 216 English children. Results: After applying exclusion criteria, the responses of 420 participants (mean age, 18.62 years; female, 54.95%) revealed good Rasch model fit, good precision (person separation = 2.33), and suboptimal targeting (-1.37). There was some evidence of multidimensionality, but disattenuated correlations between the Rasch dimension and a possible secondary dimension were high, suggesting they were measuring similar constructs. No item bias according to gender or age was detected. Spearman's correlation was 0.34 (P < 0.001) for CISSVE-CVSS17 and non-significant for CISSVE-WEMWBS. The limits of agreement for test-retest reliability were 9.67 and -8.71. Rasch analysis results indicated no difference between CISS and CISSVE. Conclusions: According to our results, CISSVE is a valid and reliable tool for measuring the symptoms assessed by CISS in Spanish people 9 to 30 years of age. Translational Relevance: CISSVE can measure convergence insufficiency symptoms in Spanish-speaking subjects.

The role of clinical diagnosis criteria on the frequency of accommodative insufficiency.

AIM: To estimate and compare the frequency of accommodative insufficiency (AI) within the same clinical population sample depending on the type of clinical criteria used for diagnosis. Comparing the frequency within the same population would help to minimize bias due to sampling or methodological variability. METHODS: Retrospective study of 205 medical records of symptomatic subjects free of any organic cause and symptoms persisting despite optical compensation evaluated. Based on the most commonly clinical diagnostics criteria found in the literature, four diagnostics criteria were established for AI (I, II, III and IV) based on subjective accommodative tests: monocular accommodative amplitude two or more diopters below Hofstetter's minimum value [15-(0.25×age)] (I, II, III, IV); failing monocular accommodative facility with minus lens, establishing the cut-off in 0 cycles per minute (cpm) (I) and in 6 cpm (II, III); failing binocular accommodative facility with minus lens, establishing the cut-off in 0 cpm (I) and in 3 cpm (II). RESULTS: The proportion of AI (95%CI) for criteria I, II, III and IV were 1.95% (0.04%-3.86%), 2.93% (0.31%-4.57%), 6.34% (1.90%-7.85%) and 41.95% (35.14%-48.76%) respectively, with a statistically significant difference shown between these values (χ2 =226.7, P<0.001). A pairwise multiple comparison revealed that the proportion of AI detected for criterion IV was significantly greater than the proportion for the rest of the criteria (P-adjusted<0.05 in all cases). CONCLUSION: The prevalence of cases of AI within the same clinical population varies with the clinical diagnostic criteria selected. The variation is statistically significant when considering the monocular accommodative amplitude as the only clinical diagnostic sign.

Comparing methods of determining addition in presbyopes.

BACKGROUND: The use of plus lenses to compensate for the reduction in the range of accommodation associated with presbyopia, brings the near point of accommodation to a comfortable distance for near visual tasks. Our aim was to compare the tentative near addition determined using the most common procedures with the final addition prescribed in presbyopic patients. METHODS: Sixty-nine healthy subjects with a mean age of 51.0 years (range 40 to 60 years) were studied. Tentative near additions were determined using seven different techniques: dynamic retinoscopy, amplitude of accommodation (AA), age-expected addition, binocular fused cross-cylinder with and without myopisation, near duochrome, and balance of negative and positive relative accommodation. The power of the addition was then refined to arrive at the final addition. RESULTS: The mean tentative near additions were higher than the final addition for every procedure except for the fused cross-cylinder without initial myopisation and age-expected addition methods. These biases were small in clinical terms (less than 0.25 D) with the exception of the AA procedure (0.34 D). The intervals between the 95% limits of agreement differed substantially and were always higher than +/-0.50 D. CONCLUSIONS: All the techniques used displayed similar behaviour and provided a tentative addition close to the final addition. Due to the wide agreement intervals observed, the likelihood of error is high and supports the idea that any tentative addition has to be adjusted according to the particular needs of each patient. Among the methods examined here, we would recommend the age-expected procedure, as this technique produced results that correlated best with the final addition.

Five levels of performance and two subscales identified in the computer-vision symptom scale (CVSS17) by Rasch, factor, and discriminant analysis.

PURPOSE: To quantify the levels of performance (symptom severity) of the computer-vision symptom scale (CVSS17), confirm its bifactorial structure as detected in an exploratory factor analysis, and validate its factors as subscales. METHODS: By partial credit model (PCM), we estimated CVSS17 measures and the standard error for every possible raw score, and used these data to determine the number of different performance levels in the CVSS17. In addition, through discriminant analysis, we checked that the scale's two main factors could classify subjects according to these determined levels of performance. Finally, a separate Rasch analysis was performed for each CVSS17 factor to assess their measurement properties when used as isolated scales. RESULTS: We identified 5.8 different levels of performance. Discriminant functions obtained from sample data indicated that the scale's main factors correctly classified 98.4% of the cases. The main factors: Internal symptom factor (ISF) and external symptom factor (ESF) showed good measurement properties and can be considered as subscales. CONCLUSION: CVSS17 scores defined five different levels of performance. In addition, two main factors (ESF and ISF) were identified and these confirmed by discriminant analysis. These subscales served to assess either the visual or the ocular symptoms attributable to computer use.

Symptoms associated with reading from a smartphone in conditions of light and dark.

Asthenopia symptoms were investigated in visually-normal subjects without computer-related vision symptoms after prolonged reading from: smartphone versus hardcopy under photopic conditions, and smartphone in conditions of ambient versus dark room illumination. After reading from the smartphone, total symptom scores and nine out of ten questionnaire symptoms were significantly worse than for the hardcopy ("blurred vision while viewing the text, "blurred distance vision after the task", "difficulty in refocusing from one distance to another", "irritated or burning eyes", "dry eyes", "eyestrain", "tired eyes", "sensitivity to bright lights" and "eye discomfort"). Mean total symptom scores and scores for "irritated or burning eyes" and "dry eyes" were significantly higher for the dark versus photopic conditions. In conclusion, prolonged smartphone reading could cause worse asthenopic symptoms than reading from a hardcopy under similar conditions. Symptoms could be even worse when reading from a smartphone in the dark.

Validity and repeatability of a new test for aniseikonia.

PURPOSE: The Aniseikonia Inspector 1.1 (AI) is a new software product to measure aniseikonia using red-green anaglyphs. The purpose of this study was to test whether the AI is a valid and reliable test. METHODS: There were two groups of sample subjects: one at risk of aniseikonia, with anisometropia greater than or equal to 1.00 D (n= 29), and a control group (n= 45). The validity was studied by comparing the measured aniseikonia with the aniseikonia simulated with size lenses. The reliability was estimated by the Bland-Altman statistical method. RESULTS: The results showed that the AI underestimated aniseikonia and that the underestimation was greater in the horizontal than in the vertical direction. The reliability was low, with biases that were clinically insignificant, but the 95% limits of agreement were around +/-2%. The behavior of the test was similar in both groups of subjects. CONCLUSIONS: The reliability of the AI is only moderate, and professionals are therefore warned to use the results of this test with caution.

Intraexaminer repeatability and agreement in stereoacuity measurements made in young adults.

AIM: To determine the repeatability and agreement of stereoacuity measurements made using some of the most widely used clinical tests: Frisby, TNO, Randot and Titmus. METHODS: Stereoacuity was measured in two different sessions separated by a time interval of at least 24h but no longer than 1wk in 74 subjects of mean age 20.6y using the four methods. The study participants were divided into two groups: subjects with normal binocular vision and subjects with abnormal binocular vision. RESULTS: Best repeatability was shown by the Frisby and Titmus [coefficient of repeatability (COR): ±13 and ±12s arc respectively] in the subjects with normal binocular vision though a clear ceiling effect was noted. In the subjects with abnormal binocular vision, best repeatability was shown by the Frisby (COR: ±69s arc) and Randot (COR: ±72s arc). In both groups, the TNO test showed poorest agreement with the other tests. CONCLUSION: The repeatability of stereoacuity measures was low in subjects with poor binocular vision yet fairly good in subjects with normal binocular vision with the exception of the TNO test. The reduced agreement detected between the tests indicates they cannot be used interchangeably.

The Computer-Vision Symptom Scale (CVSS17): development and initial validation.

PURPOSE: To develop a questionnaire (in Spanish) to measure computer-related visual and ocular symptoms (CRVOS). METHODS: A pilot questionnaire was created by consulting the literature, clinicians, and video display terminal (VDT) workers. The replies of 636 subjects completing the questionnaire were assessed using the Rasch model and conventional statistics to generate a new scale, designated the Computer-Vision Symptom Scale (CVSS17). Validity and reliability were determined by Rasch fit statistics, principal components analysis (PCA), person separation, differential item functioning (DIF), and item-person targeting. To assess construct validity, the CVSS17 was correlated with a Rasch-based visual discomfort scale (VDS) in 163 VDT workers, this group completed the CVSS17 twice in order to assess test-retest reliability (two-way single-measure intraclass correlation coefficient [ICC] and their 95% confidence intervals, and the coefficient of repeatability [COR]). RESULTS: The CVSS17 contains 17 items exploring 15 different symptoms. These items showed good reliability and internal consistency (mean square infit and outfit 0.88-1.17, eigenvalue for the first residual PCA component 1.37, person separation 2.85, and no DIF). Pearson's correlation with VDS scores was 0.60 (P < 0.001). Intraclass correlation coefficient for test-retest reliability was 0.849 (95% confidence interval [CI], 0.800-0.887), and COR was 8.14. CONCLUSIONS: The Rasch-based linear-scale CVSS17 emerged as a useful tool to quantify CRVOS in computer workers. : Spanish Abstract.

Relationship between halo size and forward light scatter.

PURPOSE: To determine the relationship between the size of a halo induced by a glare source and forward scatter or visual acuity (VA) in healthy eyes. METHOD: Measurements were made in the right eyes of 51 healthy individuals of mean age 29.3 ± 7.5 years. Halo radius was measured using the Vision Monitor and low luminance (1 cd/m(2)) optotypes presented at a distance of 2.5 m. The visual angle subtended by the radius of the halo was calculated in minutes of arc (arc min). Forward scatter or, straylight, was measured using the compensation comparison technique. Best-corrected distance VA was measured using high contrast (HC) (96%) and low contrast (LC) (10%) Bailey-Lovie logMAR letter charts under photopic (85 cd/m(2)) and mesopic (0.15 cd/m(2)) luminance conditions. RESULTS: Mean halo radius was 202 ± 43 arc min (3.4 ± 0.7°) and mean retinal straylight was 0.95 ± 0.12 log units. Mean photopic distance HC-VA and LC-VA were -0.02 ± 0.06 and 0.12 ± 0.09 logMAR, respectively. Mean mesopic distance HC-VA and LC-VA were 0.35 ± 0.11 and 0.74 ± 0.11 logMAR, respectively. Forward stepwise regression analysis revealed that halo radius was significantly correlated with straylight (r=0.45) and mesopic LC-VA (r=0.48), but not with photopic HC-VA and/or LC-VA and mesopic HC-VA. CONCLUSIONS: In healthy eyes, the larger the halo size induced by a given glare source, the greater the forward-scatter (straylight) and worse the mesopic LC-VA. Halo size seems to be independent of photopic HC-VA or LC-VA and mesopic HC-VA.

The validity and repeatability of the New Aniseikonia Test.

PURPOSE: Aniseikonia has been traditionally measured using the New Aniseikonia Test (NAT) based on red/green anaglyphs. This study was designed to establish whether the NAT is a valid and reliable test. METHODS: The NAT was tested on three groups of subjects: a control group (n = 45) and two groups of participants at risk of experiencing aniseikonia, those with anisometropia greater than or equal to 1.00 D (n = 29) and those with bilateral pseudophakia (n = 26). The validity of the test was established by comparing the measured aniseikonia with that simulated with size lenses in a double-blind study. Repeatability was evaluated by comparing the results obtained at two different time points. RESULTS: Our results indicate that the NAT underestimates aniseikonia and more so in the horizontal than in the vertical direction. Repeatability was poor, although biases were clinically insignificant. However, the 95% limits of agreement were around +/-2%. The behavior of the test was similar in the three groups of subjects. CONCLUSIONS: We conclude that the repeatability of the NAT is not very high and recommend that clinicians be cautious when interpreting the results of this test.

Bayesian model of Snellen visual acuity.

A Bayesian model of Snellen visual acuity (VA) has been developed that, as far as we know, is the first one that includes the three main stages of VA: (1) optical degradations, (2) neural image representation and contrast thresholding, and (3) character recognition. The retinal image of a Snellen test chart is obtained from experimental wave-aberration data. Then a subband image decomposition with a set of visual channels tuned to different spatial frequencies and orientations is applied to the retinal image, as in standard computational models of early cortical image representation. A neural threshold is applied to the contrast responses to include the effect of the neural contrast sensitivity. The resulting image representation is the base of a Bayesian pattern-recognition method robust to the presence of optical aberrations. The model is applied to images containing sets of letter optotypes at different scales, and the number of correct answers is obtained at each scale; the final output is the decimal Snellen VA. The model has no free parameters to adjust. The main input data are the eye's optical aberrations, and standard values are used for all other parameters, including the Stiles-Crawford effect, visual channels, and neural contrast threshold, when no subject specific values are available. When aberrations are large, Snellen VA involving pattern recognition differs from grating acuity, which is based on a simpler detection (or orientation-discrimination) task and hence is basically unaffected by phase distortions introduced by the optical transfer function. A preliminary test of the model in one subject produced close agreement between actual measurements and predicted VA values. Two examples are also included: (1) application of the method to the prediction of the VAin refractive-surgery patients and (2) simulation of the VA attainable by correcting ocular aberrations.