The Development, Assessment, and Selection of Questionnaires

COVD-QOL questionnaire: An adaptation for school vision screening using Rasch analysis

Purpose

To adapt the College of Optometrist in Vision Development (COVD-QOL) questionnaire as a vision screening tool for primary school children.

Methods

An interview session was conducted with children, teachers or guardians regarding visual symptoms of 88 children (45 from special education classes and 43 from mainstream classes) in government primary schools. Data was assessed for response categories, fit items (infit/outfit: 0.6–1.4) and separation reliability (item/person: 0.80). The COVD-QOL questionnaire results were compared with vision assessment in identifying three categories of vision disorders: reduce visual acuity, accommodative response anomaly and convergence insufficiency. Analysis on the screening performance using the simplified version of the questionnaire was evaluated based on receiver-operating characteristic analysis for detection of any type of target conditions for both types of classes. Predictive validity analysis was used a Spearman rank correlation (>0.3).

Results

Two of the response categories were underutilized and therefore collapsed to the adjacent category and items were reduced to 14. Item separation reliability for the simplified version of the questionnaire was acceptable (0.86) but the person separation reliability was inadequate for special education classes (0.79) similar to mainstream classes (0.78). The discriminant cut-off score of 9 (mainstream classes) and 3 (special education classes) from the 14 items provided sensitivity and specificity of (65% and 54%) and (78% and 80%) with Spearman rank correlation of 0.16 and 0.40 respectively.

Conclusion

The simplified version of COVD-QOL questionnaire (14-items) performs adequately among children in special education classes suggesting its suitability as a vision screening tool.

The impact of cataract, cataract types, and cataract grades on vision-specific functioning using Rasch analysis

PURPOSE

To determine the impact of cataracts and their types and grades on vision-specific functioning.

DESIGN

Prospective population-based cross-sectional study.

METHODS

The Singapore Indian Eye Study examined 3400 of 4497 (75.6% response rate) ethnic Indians 40 years of age and older living in Singapore. Three thousand one hundred sixty-eight (93.2%) fulfilled inclusion criteria with complete information for final analysis. Cataracts were assessed on slit-lamp examination and were graded according to the Lens Opacity Classification System III. Vision-specific functioning scores were explored with the Visual Function scale, validated using Rasch analysis.

RESULTS

Two hundred sixty-nine (8.5%) and 740 (23.4%) of the study participants had unilateral and bilateral cataracts, respectively, and 329 (10.4%), 800 (25.2%), and 128 (4.1%) participants had nuclear, cortical, and posterior subcapsular (PSC) cataracts, respectively. In multivariate linear regression models, the presence of bilateral rather than unilateral cataract (β = -0.12; 95% confidence interval, -0.20 to 0.00) was associated independently with poorer vision-specific functioning, even after adjusting for undercorrected refractive error (β = -0.11; 95% confidence interval, -0.21 to 0.00). Bilateral nuclear, cortical, and PSC cataracts also were associated with poorer vision-specific functioning (β = -0.31, -0.15, and -1.15, respectively), with combinations of them having even greater impact. Significantly poorer vision-specific functioning occurred at Lens Opacity Classification System grades 4 (nuclear opalescence), 5 (nuclear color), 3 (cortical), and 1 (PSC) or higher.

CONCLUSIONS

People with bilateral but not unilateral cataracts experience difficulty with performing vision-specific daily activities independent of refractive error, with PSC cataracts and cataract combinations having the greatest impact. Cataract types cause poorer vision-specific functioning beginning at different severity grades.

Evaluating the Construct Validity of the Kidscreen-52 Quality of Life Questionnaire within a South African Context

The absence of a suitable measure to assess the health-related quality of life (HRQoL) of children and adolescents in South Africa, led to the use of the KIDSCREEN-52 questionnaire, which was developed and standardised in Europe. The current study is part of a broader study conducted in the Western Cape, which used the KIDSCREEN-52 to explore the influence of exposure to community violence on the subjective HRQoL of a sample of South African adolescents. This study aimed to investigate the reliability and construct validity of the KIDSCREEN-52 in a South African context. The broader study employed stratified interval criterion sampling to select 565 Grade 9 learners, aged 14–18. Participants were selected from six public schools in areas specified by the South African government as comprising key nodal areas in terms of crime in the Western Cape. The dataset for the current study comprised all participants (N = 565) of the primary study. As the initial step in validation of the KIDSCREEN-52 in South Africa, the current study examined its factor structure by means of exploratory factor analysis, using principal component analysis with oblimin rotations. It also assessed the internal consistency reliability of each of the scales, using Cronbach's alpha. Exploratory factor analysis extracted 10 factors as identified by previous studies, with some deviation in the loadings of the last three factors. Items of two scales (“Feelings” and “About Yourself”) divided into three scales, and “Bullying” items were not sufficiently presented in the factor solution. Internal consistency of the measure was shown to be acceptable to good, with Cronbach's alpha values ranging from 0.76 to 0.81 for the 10 scales.

A new look at the WHOQOL as health-related quality of life instrument among visually impaired people using Rasch analysis

PURPOSE

To examine the psychometric characteristics of the World Health Organization quality of life instrument-modified Indian version (modified WHOQOL) and its subscales in adults with visual impairment (VI) using Rasch analysis.

METHODS

Cross-sectional data were of people aged ≥40 years with VI (n = 1,333) who responded to the modified WHOQOL in the Andhra Pradesh Eye Disease Study, India. Rasch analysis was used to explore the instrument and its subscales for key indices such as measurement precision by person separation reliability, PSR (i.e., discrimination between strata of participants' health-related QOL [HRQOL], recommended minimum value 0.8), unidimensionality (i.e., measurement of a single construct), and targeting (i.e., matching of item difficulty to participants' HRQOL).

RESULTS

Rasch-guided iterative approach including category re-organization to enable threshold ordering and item deletion to overcome multidimensionality resulted in a unidimensional 9-item WHOQOL and a 6-item level of independence (LOI) subscale with adequate PSR (0.81 and 0.82, respectively). Targeting was sub-optimal for both (-1.58 logits for WHOQOL and -2.55 logits for the subscale). Remaining subscales were dysfunctional.

CONCLUSIONS

The WHOQOL and LOI subscale can be improved and shortened, and the Rasch-revised versions are likely to assess the HROQL of VI patients best because of their brevity, reliability, and unidimensionality.

Evaluation of the Adult Strabismus-20 (AS-20) questionnaire using Rasch analysis

PURPOSE

To further refine the Adult Strabismus 20 (AS-20) health-related quality of life (HRQOL) questionnaire using Rasch analysis.

METHODS

Rasch analysis was performed independently on the original AS-20 using the following steps: dimensionality, response ordering, local dependence, infit and outfit analyses, differential item functioning, subject targeting, and confirmatory dimensionality.

RESULTS

Two subscales were present in each of the original AS-20 subscales, for a total of 4 subscales, which were labeled "self-perception," "interaction," "reading function," and "general function." Response ordering was appropriate for 3 of the subscales but required reduction to 4 response options for the fourth subscale. No notable local dependence was found for any subscale. As a result of fit analysis, 2 items were removed, 1 each from 2 subscales. No significant differential item functioning was seen for sex or age. The resulting 5-item self-perception subscale and 4-item reading function subscale are reliable and target the adult strabismus patient cohort appropriately. The resulting 5-item interaction subscale and 4-item general function subscale have less than optimal reliability.

CONCLUSIONS

The AS-20 benefits from reduction to 4 subscales (self-perception, interaction, reading function, and general function) and reducing the response options in the general function subscale from 5 to 4 options. The refined AS-20 may prove to be even more responsive to HRQOL changes in adult strabismus following treatment or changes over time.

[Measurement of glaucoma-specific functionality with the GQL-15 and correlation with parameters of visual function]

INTRODUCTION

Glaucoma is one of the leading causes of irreversible blindness worldwide and can have a significant impact on patient quality of life and vision-related functioning. The Glaucoma Quality of Life 15 (GQL-15) questionnaire is a disease-specific instrument to evaluate and quantify functional impairment of patients with glaucoma. This study evaluated the German version of the GQL-15 including correlations with perimetric parameters.

METHODS

A German version of the GQL-15 containing 15 items was developed and evaluated in 98 patients with glaucoma in different stages of the disease. The GQL-15 results were correlated with the perimetric parameters mean deviation (MD) and pattern standard deviation (PSD) of the better and worse eye. Classical and probabilistic test analyses (Rasch model) were performed.

RESULTS

The mean GQL-15 value was 77.3 ± 21.7 (SD) and most items of the GQL-15 correlated significantly with the MD of the worse eye (r = -0.416; p = 0.0014) and the better eye (r = -0.304; p = 0.02). There was also a highly significant correlation between glaucoma-specific QoL and visual acuity. A short version containing nine items yielding a higher psychometric performance can also be used.

CONCLUSIONS

The German version of the GQL-15 is a potent instrument to evaluate impairment in vision-specific functioning of patients with glaucoma. The GQL-15 values are better correlated with the sensitivity of the eye with the more severe glaucomatous damage. The data can help for a better understanding of individual patient impairment to improve medical advice and therapy of patients with glaucoma.

Social and emotional impact of diabetic retinopathy: a review

People with vision-threatening diabetic retinopathy are likely to experience enhanced social and emotional strain. Critically, those with both vision-threatening diabetic retinopathy and psychosocial problems may have significantly reduced levels of functioning compared with psychologically healthy counterparts. This can cause inadequate compliance, increased strain on family functioning, worse diabetes control, increased progression of diabetic retinopathy and, consequently, further psychosocial stress resulting in a number of concerning implications for disease management, clinical outcomes and healthcare costs. However, the emotional and social health consequences of diabetic retinopathy have not yet been systematically explored. This information is crucial as it allows for a targeted approach to treatment and prevention and avoidance of the potentially detrimental implications described above. Therefore, this paper reviews the current qualitative and quantitative evidence regarding the social and emotional impact of diabetic retinopathy and identifies directions for future research. Key search terms were applied to the electronic databases Pubmed, ISI Web of Science and Embase and the bibliographies of relevant papers were systematically reviewed for additional references. Overall, the evidence suggests that diabetic retinopathy and associated vision loss have several debilitating effects, including disruption of family functioning, relationships and roles; increased social isolation and dependence; and deterioration of work prospects resulting in increased financial strain. Adverse emotional responses include fear, anxiety, vulnerability, guilt, loss of confidence, anger, stress and self-perception issues. However, the research to date is largely qualitative in nature, with most quantitative studies being small, cross-sectional and somewhat outdated. Similarly, the outcome measures used in many studies to date are suboptimal in terms of content and validity. Therefore, this review identifies the need for improved outcome measures to provide valid, meaningful measurement of the social and emotional impact of diabetic retinopathy and discusses potential directions for future research such as item banking and computer adaptive testing.

Impact of a low-vision self-management program on informal caregivers

PURPOSE

To evaluate caregivers' experiences and outcomes following attendance at a patient-centered group-based self-management program called "Living with Low Vision."

METHODS

Participants were caregivers of adults with low vision. A pre-post study design evaluated the impact of the program on single-item indicators that assessed levels of understanding of low vision, awareness of devices, aids and practical strategies, and questionnaires to assess confidence to deal with low vision, self-efficacy, and emotional well being. Participants formed three groups: (1) those who attended the program [intervention group 1 (IG1)] and received a take-home pack; (2) those who received a take-home pack only [intervention group 2 (IG2)]; and (3) those who received no intervention [comparison group (CG)].

RESULTS

Sixty participants (IG1 = 16, IG2 = 33, CG = 11) with mean (SD) age 67.2 years (SD = 14.8) were recruited. Half (n = 31; 51.7%) were the spouse of the adults with low vision. With the exception of two single-item indicators that assessed awareness of low-vision aids and practical strategies; no significant group differences on follow-up scores between the three study groups were found on any measure. Compared with CG participants, IG1 and IG2 participants demonstrated significantly greater awareness of low-vision aids and practical strategies (p < 0.05, for all). In addition, IG1 participants demonstrated significantly improved awareness of practical strategies than IG2 participants (p = 0.024). Most IG1 participants (n = 10; 62.5%) agreed that the program was relevant and helpful, and most would recommend it to other caregivers.

CONCLUSIONS

Involving caregivers in a patient-centered group-based self-management program and providing them with an informative take-home self-help pack improved their awareness of low-vision aids, devices, and practical strategies. Our findings should be followed up with larger studies to clearly identify optimal ways of providing caregivers with information and problem-solving skills to effectively manage the demands of low vision.

The unidimensional self-efficacy scale for MS (USE-MS): developing a patient based and patient reported outcome

Background:

Self-efficacy concerns the individual’s belief that he or she is capable of performing a certain task and producing a desired effect, i.e. it reflects the person’s perceptions of their capability for specific tasks, as distinct from their actual ability. Self-efficacy has been shown to influence motivation, psychological well-being, adherence with treatment regimes and quality of life in multiple sclerosis and other conditions.

Objective:

To develop a unidimensional scale of MS self-efficacy with robust psychometric properties, suitable for patient self report.

Methods:

A questionnaire pack covering three MS self-efficacy scales, the Dispositional Resilience Scale and demographic data was posted to MS patients from two MS databases. Data underwent Rasch analysis.

Results:

Response rate was 309/600 (51.5%). None of the existing MS self-efficacy scales were unidimensional. A new 12-item scale, created by combining items from our two scales, was shown to fit the Rasch model, was unidimensional, and invariant for gender, education and disease duration.

Conclusion:

The Unidimensional Self-Efficacy scale for MS (USE-MS) provides a simple summated scale for an ordinal estimate of a persons’ self efficacy. A transformation to interval scaling is available for use in the calculation of change scores and effect sizes.

The relative impact of vision impairment and cardiovascular disease on quality of life: the example of pseudoxanthoma elasticum

Objective

To investigate the impact of pseudoxanthoma elasticum (PXE), a rare hereditary disease of concurrent vision impairment (VI) and cardiovascular complications (CVCs), on vision-related (VRQoL) and health-related quality of life (HRQoL).

Methods

VRQoL and HRQoL were assessed using the Impact of Vision Impairment (IVI) questionnaire and the Short Form Health Survey (SF-36) in 107 PXE patients. Patients were stratified into four groups: A = no VI or CVC; B = CVCs only; C = VI only; and D = both VI and CVCs.

Results

Following Rasch analysis, the IVI was found to function as a vision-specific functioning and emotional well-being subscale, and the SF-36 as a health-related physical functioning and mental health subscale. The presence of VI and CVC were significant predictors of vision-specific functioning and emotional well-being (p < 0.001), with a clinically meaningful decrement in vision-specific functioning in patients with VI. No associations were found for the SF-36 Physical Functioning and Mental Health scores between any groups.

Conclusions

Vision impaired patients with PXE report significantly poorer vision-specific functioning than PXE patients without VI. In contrast, the relative impact of PXE on reported general HRQoL was much less. Our results suggest that vision impairment has the larger impact on QoL in this sample.

The outcome of cataract surgery measured with the Catquest-9SF

PURPOSE

The purpose of this study was to use the Catquest-9SF to measure cataract surgery outcomes, and to use Rasch analysis to test the psychometric properties of this questionnaire, including its validity and responsiveness.

METHODS

Patients were recruited as consecutive cataract surgery patients during 1 month at six surgical units in Sweden (via the National Cataract Register). The patients completed the questionnaire before surgery and 3 months after. The Catquest-9SF data were assessed for fit to the Rasch model using version 3.63.2 of the WINSTEPS software (Winsteps.com, Beaverton, OR, USA). Both preoperative and postoperative questionnaires were included in the analysis. The responsiveness to cataract surgery was calculated as the effect size.

RESULTS

Completed questionnaires before and after surgery were received from 846 patients. The Rasch analysis showed that the category thresholds were ordered. All items fit a single overall construct (infit range 0.79-1.40; outfit range 0.74-1.40). The ability to discriminate different strata of person ability was good, with a real patient separation of 2.58 and patient separation reliability of 0.87. The questionnaire showed unidimensionality and was largely free from differential item functioning. The item difficulty was reasonably well targeted to both preoperative and postoperative patient ability. The Catquest-9SF Rasch score correlated significantly with visual acuity, and cataract surgery resulted in a significant improvement with an effect size of 1.8.

CONCLUSION

The Catquest-9SF shows excellent psychometric properties, as demonstrated by Rasch analysis. It is highly responsive to cataract surgery, and its brevity (nine items) makes it well suited for use in daily clinical practice.

Rasch analysis of the Ocular Surface Disease Index (OSDI)

PURPOSE

The Ocular Surface Disease Index (OSDI) is a 12-item scale for the assessment of symptoms related to dry eye disease and their effect on vision. Its reliability and validity have been investigated within the classical test theory framework and, more recently, using Rasch analysis. The purpose of the present analysis was to more completely investigate the functioning of its response category structure, the validity of its three subscales, and the unidimensionality of the latent construct it is intended to assess.

METHODS

Responses to the OSDI from 172 females participating in the Dry Eye in Postmenopause (DEiM) study who had previously been diagnosed with dry eye or reported significant ocular irritation and dryness were analyzed. Response category structure and item fit statistics were evaluated for assessment of model fit. Person separation statistics were used to examine the validity of the subscales. Unidimensionality was assessed by principal component analysis (PCA) of model residuals.

RESULTS

The recommended five-category response structure resulted in disordered response thresholds. A four-category structure resulted in ordered thresholds. Item infit statistics were acceptable for all 12 items. Person separation with this category structure was adequate, with a person separation index of 2.16. None of the three subscales demonstrated adequate person separation. PCA showed one other significant factor onto which the three environmental items loaded significantly.

CONCLUSIONS

All items demonstrated acceptable fit to the model after collapsing categories to order the response thresholds. The original subscales did not prove valid, and there is some evidence of multidimensionality and poor targeting.

Short form of the Chinese version Diabetes Quality of Life for Youth Scale: a psychometric testing in Taiwanese adolescents with type 1 diabetes

OBJECTIVE

To test the psychometric properties of the short form of the Chinese version Diabetes Quality of Life for Youth scale (C-DQOLY-SF).

RESEARCH DESIGN AND METHODS

A 30-item C-DQOLY-SF was administered to 371 adolescents with type 1 diabetes. Exploratory and confirmatory factor analysis, correlation with HbA(1c), internal consistency, and test-retest reliability were used to examine the psychometric characteristics of C-DQOLY-SF.

RESULTS

A 25-item questionnaire with three correlated second-order factor structures best fitted data. Scores on the 25-item C-DQOLY-SF significantly correlated with HbA(1c) values. Cronbach's α and ICCs of each scale and subscale ranged from 0.77 to 0.90 and from 0.70 to 0.92, respectively.

CONCLUSIONS

The C-DQOLY-SF has satisfactory reliability and validity. The C-DQOLY-SF can be conveniently used in clinical settings to assess the quality of life of adolescents with type 1 diabetes.

The impact of cataract surgery questionnaire: re-evaluation using Rasch analysis

PURPOSE

The Impact of Cataract Surgery (ICS) questionnaire was designed to assess cataract surgery outcomes. The aim of this study was to describe the psychometric properties of the ICS questionnaire using the Rasch model in a cataract population.

METHODS

Ninety-one patients waiting to undergo cataract surgery in the first or second eye at the Flinders Medical Centre, Adelaide, South Australia self-administered the four-item ICS questionnaire. Rasch analysis was performed to assess behaviour of response categories, ability to differentiate between participants' visual abilities (person separation; minimum acceptable 2.0), if items measure a single underlying construct [i.e. unidimensionality assessed by fit statistics and further by principal components analysis (PCA)] and matching of item difficulty to participant ability (targeting; ideal < 0.5 logits). Adequate person separation was defined as basic requirement for a measure, failing which further assessment such as PCA was not performed.

RESULTS

The four-item ICS questionnaire did not meet the required measurement properties (person separation zero). Response categories did not behave as intended, requiring the collapsing of categories for one item (read ordinary newspaper-size print). One item misfit (estimating distance) indicating that it was not measuring the same construct as other items. However, person separation failed to improve following the deletion of this item. Targeting was -0.46 logits, indicating that the item difficulty was well suited to the visual abilities of the participants.

CONCLUSION

In its present form, the ICS is unsuitable for visual disability assessment in patients awaiting cataract surgery. Other, better visual function questionnaires are available and preferred.

Statistical guidelines for clinical studies of human vision

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.

Patient-reported outcomes (PRO's) in glaucoma: a systematic review

The aim of this review was to summarize literature in view of patient-reported outcome (PRO) instruments for glaucoma and provide guidance on how outcomes are best assessed based on evidence about their content and validity. A systematic literature review was performed on papers describing the developmental process and/or psychometric properties of glaucoma or vision-specific PRO-instruments. Each of them was assessed on their adherence to a framework of quality criteria. Fifty-three articles were identified addressing 27 PRO-instruments. In all, 18 PRO's were developed for glaucoma and 9 for diverse ophthalmologic conditions. Seven instruments addressed functional status, 11 instruments quality of life and 9 instruments disease and treatment-related factors. Most of the instruments demonstrated only partially adherence to predefined quality standards. The tools for assessing functional status were of poor quality, while the Glaucoma Quality of Life Questionnaire and the Vision Quality of Life Index were well-developed QoL measures, yet only validated using classical techniques. The Rasch-scaled QoL-tools, IVI and VCM1 need to improve their item-content for glaucoma patients. The questionnaires to measure adherence should improve their validity and the Treatment Satisfaction Survey for Intra Ocular Pressure pops out as the highest quality tool for measuring topical treatment side effects. This review revealed that most PRO-instruments demonstrated poor developmental quality, more specifically a lack of conceptual framework and item generation strategies not involving the patients' perspective. Psychometric characteristics were mostly tested using classical validation techniques.

Is the pediatric quality of life inventory valid for use in preschool children with refractive errors?

PURPOSE

To determine the psychometric validity of the pediatric quality of life inventory (PedsQL 4.0) in assessing the impact of refractive errors on health-related quality of life (HRQoL) in preschool children in Singapore.

METHODS

Parents of toddlers (aged 25 to 48 months) and young children (49 to 72 months) completed the PedsQL 4.0, an HRQoL scale as part of population-based trial in Singapore. The outcome measures were the overall score, and the "physical"; "emotional"; "social"; and "school" functioning subscales. Rasch analysis was used to validate the PedsQL 4.0.

RESULTS

Parents of 939 (48.9%) toddlers and 982 (51.1%) young children completed the PedsQL 4.0 survey. The overall mean (±standard deviation) spherical equivalence for the right eye was 0.47 ± 1.13 diopter (D) for toddlers and 0.74 ± 1.22 D for young children. One hundred forty-nine (15.9%) toddlers and 90 (9.2%) young children were considered myopic (≥-0.50 D). Most participants (n = 1286, 89.6%) had presenting visual acuity 6/9 or better. Rasch analysis showed evidence of disordered category thresholds and poor person-item targeting for both groups. The separation reliability was 0.00 for toddlers and 0.03 for young children, indicating there was no variance in both samples. The PedsQL 4.0 overall and subscale scores displayed substantial multidimensionality as the variance values explained by the measures was <25% in both groups. A minimum value of 60% is usually considering acceptable.

CONCLUSIONS

The PedsQL 4.0 in its current state is not a valid psychometric scale to effectively evaluate the impact of refractive errors on HRQoL in preschool children in Singapore.

Choosing appropriate patient-reported outcomes instrument for glaucoma research: a systematic review of vision instruments

PURPOSE

To identify vision Patient-Reported Outcomes instruments relevant to glaucoma and assess their content validity.

METHODS

MEDLINE, MEDLINE in Process, EMBASE and SCOPUS (to January 2009) were systematically searched. Observational studies or randomised controlled trials, published in English, reporting use of vision instruments in glaucoma studies involving adults were included. In addition, reference lists were scanned to identify additional studies describing development and/or validation to ascertain the final version of the instruments. Instruments' content was then mapped onto a theoretical framework, the World Health Organization International Classification of Functioning, Disability and Health. Two reviewers independently evaluated studies for inclusion and quality assessed instrument content.

RESULTS

Thirty-three instruments were identified. Instruments were categorised into thirteen vision status, two vision disability, one vision satisfaction, five glaucoma status, one glaucoma medication related to health status, five glaucoma medication side effects and six glaucoma medication satisfaction measures according to each instruments' content. The National Eye Institute Visual Function Questionnaire-25, Impact of Vision Impairment and Treatment Satisfaction Survey-Intraocular Pressure had the highest number of positive ratings in the content validity assessment.

CONCLUSION

This study provides a descriptive catalogue of vision-specific PRO instruments, to inform the choice of an appropriate measure of patient-reported outcomes in a glaucoma context.

Comparison of scoring approaches for the NEI VFQ-25 in low vision

PURPOSE

The aim of this study was to evaluate different approaches to scoring the National Eye Institute Visual Functioning Questionnaire-25 (NEI VFQ-25) in patients with low vision including scoring by the standard method, by Rasch analysis, and by use of an algorithm created by Massof to approximate Rasch person measure. Subscale validity and use of a 7-item short form instrument proposed by Ryan et al. were also investigated.

METHODS

NEI VFQ-25 data from 50 patients with low vision were analyzed using the standard method of summing Likert-type scores and calculating an overall average, Rasch analysis using Winsteps software, and the Massof algorithm in Excel. Correlations between scores were calculated. Rasch person separation reliability and other indicators were calculated to determine the validity of the subscales and of the 7-item instrument.

RESULTS

Scores calculated using all three methods were highly correlated, but evidence of floor and ceiling effects was found with the standard scoring method. None of the subscales investigated proved valid. The 7-item instrument showed acceptable person separation reliability and good targeting and item performance.

CONCLUSIONS

Although standard scores and Rasch scores are highly correlated, Rasch analysis has the advantages of eliminating floor and ceiling effects and producing interval-scaled data. The Massof algorithm for approximation of the Rasch person measure performed well in this group of low-vision patients. The validity of the subscales VFQ-25 should be reconsidered.

Derivation of the acceptance and self-worth adjustment scale

PURPOSE

The original 55-item Nottingham Adjustment Scale (NAS) is a first generation self-report instrument constructed using classical test theory to evaluate adjustment to vision loss. This study assesses the function of the NAS using Rasch analysis in a sample of adults with visual impairment and presents a revised second-generation instrument.

METHODS

Ninety-nine subjects with established vision loss (median onset 5 years) were administered the NAS. Rasch analysis was performed to: (1) determine optimum response scale function, (2) aid item reduction, (3) determine reliability indices and item targeting, (4) assess unidimensionality using Rasch-based principal component analysis, (5) assess differential item functioning (notable defined as >1.0 logit), and (6) formulate person measures to correlate with Geriatric Depression Scale scores and distance visual acuity to indicate convergent and discriminant validity, respectively.

RESULTS

Response categories exhibited underutilization, which when repaired improved response scale functioning and ordered structural calibrations. Misfitting items were removed iteratively until all items had mean-square infit and outfit values of 0.70 to 1.30. However, principal component analysis confirmed insufficient unidimensionality (two contrasts identified, eigenvalues 2.4 and 2.3). Removal of these contrasts and two further iterations restored unidimensionality. Despite item mistargeting (1.58 logits), the revised 19-item instrument demonstrated good person (0.85) and item (0.96) reliability coefficients, good convergent and discriminant validity, and no systematic differential item functioning. The resultant 19-item instrument was termed the Acceptance and Self-Worth Adjustment Scale (AS-WAS).

CONCLUSIONS

In those with established vision loss, the 19-item Acceptance and Self-Worth Adjustment Scale is a reliable and valid instrument that estimates the level of adjustment concerned with acceptance, attitudes, self-esteem, self-efficacy, and locus of control. An additional measure of depression and anxiety is recommended to assess adjustment in a broader sense. Confirmation of item ordering is required if to be used in those with newly acquired vision loss.

The impact of reduced distance and near vision on the quality of life of adults in Timor-Leste

PURPOSE

To determine the independent, relative, and combined impact of reduced distance and near vision on the vision-specific quality of life (VS QOL) of adults in Timor-Leste.

DESIGN

A population-based cross-sectional eye health survey was conducted in urban and rural areas in Timor-Leste.

PARTICIPANTS

Participants were 40 years or older. Those with better eye presenting distance vision worse than 6/18, and every third participant with 6/18 or better vision, completed the VS QOL questionnaire: in total 704 of the 1414 participants.

METHODS

Distance and near visual acuities were measured and eye health was assessed. The VS QOL questionnaire administered by interview was analyzed using Rasch analysis, univariate analysis, and linear regression to determine associations between VS QOL, demographic factors, and levels of visual impairment.

MAIN OUTCOME MEASURES

The Timor-Leste VS QOL questionnaire results.

RESULTS

Rasch analysis confirmed that for participants both with and without visual impairment, the Timor-Leste VS QOL questionnaire provided a valid and reliable measure, was unidimensional, and had appropriate response categories. There was a consistent pattern of deterioration in VS QOL as vision worsened: for each category of distance- and near-vision impairment, there was an independent and significant change in Timor-Leste VS QOL scores between no visual impairment and either mild, moderate, or severe impairment (P < 0.05). Combined distance- and near-vision impairment was associated with a greater impact on VS QOL than categories separately, the impact of severe distance- and near-vision impairment being the greatest and clinically significant: -3.05 (95% confidence interval [CI], -3.60 to -2.49; P<0.05; and 95% CI, <-1.0). Distance vision (37.2%) contributed relatively more than near vision (4.7%) to the total variance in VS QOL (41.9%). Older people, those not married, not literate, and rural dwellers had significantly worse Timor-Leste VS QOL scores (P < 0.05).

CONCLUSIONS

This study provides evidence of independent dose-response relationships between distance- and near-vision impairment and poorer VS QOL. Distance-vision impairment had a relatively larger impact on VS QOL than near-vision impairment. Combined distance- and near-vision impairment was associated with a greater impact on VS QOL compared with the independent impact of distance- or near-vision impairment at similar levels.

Assessment of functional vision and its rehabilitation

This article, based on a report prepared for the International Council of Ophthalmology (ICO) and the International Society for Low Vision Research and Rehabilitation (ISLRR), explores the assessment of various aspects of visual functioning as needed to document the outcomes of vision rehabilitation. Documenting patient abilities and functional vision (how the person functions) is distinct from the measurement of visual functions (how the eye functions) and also from the assessment of quality of life. All three areas are important, but their assessment should not be mixed. Observation of task performance offers the most objective measure of functional vision, but it is time-consuming and not feasible for many tasks. Where possible, timing and error rates provide an easy score. Patient response questionnaires provide an alternative. They may save time and can cover a wider area, but the responses are subjective and proper scoring presents problems. Simple Likert scoring still predominates but Rasch analysis, needed to provide better result scales, is gaining ground. Selection of questions is another problem. If the range of difficulties does not match the range of patient abilities, and if the difficulties are not distributed evenly, the results are not optimal. This may be an argument to use different outcome questions for different conditions. Generic questionnaires are appropriate for the assessment of generic quality of life, but not for specific rehabilitation outcomes. Different questionnaires are also needed for screening, intake and outcomes. Intake questions must be relevant to actual needs to allow prioritization of rehabilitation goals; the activity inventory presents a prototype. Outcome questions should be targeted at predefined rehabilitation goals. The Appendix cites some promising examples. The Low Vision Intervention Trial (LOVIT) is an example of a properly designed randomized control study, and has demonstrated the remarkable effectiveness of vision rehabilitation. It is hoped that further similar studies will follow.

Validation of the visual disability questionnaire (VDQ) in India

PURPOSE

To validate visual disability questionnaire (VDQ) in patients with low vision in India, and explore whether the two latent traits "importance" and "difficulty" associated with performance of daily activities are valid and independent constructs.

METHODS

The VDQ consisting of 25 items was administered verbally to 137 subjects with low vision aged 16 to 89 years. Responses for each item were rated for importance and difficulty using a 5-category Likert scale. Rasch analysis was used to estimate interval measures of response ratings.

RESULTS

Subjects could discriminate only three response categories for importance and difficulty. Content validity was demonstrated by good separation indices for importance (4.24 and 2.59 for the item and person parameters, respectively) and difficulty ratings (7.64 and 3.33, respectively). High reliability scores were recorded for importance (0.95 and 0.87) and difficulty ratings (0.98 and 0.92). The most important items were "grooming" (1.15 logits) and "reading newspaper" (0.97 logits). Although "threading a needle" was the least important item (-2.79 logits), it was the most difficult task (3.13 logits). The least difficult item was moving around in familiar places (-2.51 logits). A poor correlation was observed between the item measures (r = -0.19, p = 0.34) and also between person measures (r = 0.18, p = 0.03) of importance and difficulty.

CONCLUSIONS

The VDQ is a valid questionnaire with importance and difficulty ratings found to be independent constructs. This questionnaire could be used to prioritize the goals for rehabilitation intervention in patients with low vision.

Nearpoint phorias after nearwork predict ADHD symptoms in college students

PURPOSE

Phorometric findings have been observed to change with stress. We test the hypothesis that postnearwork phorias predict symptoms that have been theorized to result from nearwork-induced visual stress.

METHODS

We measured nearpoint and farpoint dissociated phorias in 37 unselected college students with an alternate cover test both before and after a challenging reading comprehension test. We also assessed a broad range of putative attention deficit hyperactivity disorder (ADHD)-related symptoms with the Nadeau College-level ADHD Questionnaire.

RESULTS

For phorias measured at nearpoint after nearwork, greater deviation from the median phoria (three exophoria) predicted higher symptoms (rho (35) = 0.52, p < 0.001), whether that deviation was in a convergent or a divergent direction (both rho's (18) = >0.48, p's < 0.04). An analogous result was obtained for "distance-near" stimulus accommodative convergence to accommodation (AC/A) ratios calculated from phorias, where greater deviation from median postnearwork AC/A ratio predicted higher symptoms (rho (35) = 0.52, p < 0.0001). Symptoms did not correlate with prenearwork phorias, prenearwork AC/A ratios, or postnearwork farpoint phorias (p's > 0.05).

CONCLUSIONS

Phorias postnearwork, but not prenearwork, predicted self-reported ADHD-related symptoms in college students. These results link binocular imbalance immediately after sustained nearwork to symptoms theorized to result from nearwork-induced visual stress.

Catquest-9SF patient outcomes questionnaire: nine-item short-form Rasch-scaled revision of the Catquest questionnaire

PURPOSE

To assess and optimize the Catquest questionnaire for measuring patient-reported outcomes of cataract surgery using Rasch analysis.

SETTING

Fifty-eight ophthalmic surgical units in Sweden.

METHODS

Catquest questionnaires (n = 21364) from the Swedish National Cataract Register were selected and randomized to 2 groups. Data from 10486 questionnaires were comprehensively Rasch analyzed using a 4-Andrich rating scale model in Winsteps software. A revised version of Catquest was developed (Catquest-9SF) and tested in 10886 patients for validity and responsiveness to cataract surgery.

RESULTS

Only the visual disability subscale formed a valid measurement scale. This could be enhanced through the addition of the 2 global assessment items; however, the symptoms and frequency of performing the activities items did not contribute to the measurement. The 9-item short-form version (Catquest-9SF) had ordered response thresholds and good person separation (2.65) and was largely free from differential item functioning. All items fit a single overall construct (infit range, 0.75 to 1.29; outfit range, 0.70 to 1.39) and unidimensional by principal components analysis. The items were well targeted to the preoperative participants (0.34 logit difference in means). The score correlated with visual acuity (r = 0.43 preoperatively; r = 0.48 postoperatively) and was highly responsive to cataract surgery (preoperatively -0.32 +/- 2.15 logits; postoperatively -3.21 +/- 2.50 logits (P<.0001).

CONCLUSIONS

The 9-item Rasch-scaled Catquest-9SF was highly valid in measuring visual disability outcomes of cataract surgery. Its brevity makes it suited to routine clinical use, and a raw-data to Rasch-measure conversion simplifies application.

Modification and validation of the Lysholm Knee Scale to assess articular cartilage damage

OBJECTIVE

The Lysholm Knee Scale is an 8-item questionnaire originally designed as an outcome measure for ligament reconstruction but is commonly used as a measure for knee chondral damage. This study tests the scale's internal construct validity using the Rasch model, a measurement model which sets strict standards for the quality of measurement derived from the scale. The study also investigates the level of agreement between scores from patients and physiotherapists; and reviews the present weighting system.

DESIGN

One hundred and fifty-seven patients with knee chondral damage awaiting surgery completed the Lysholm as part of a multicentre clinical trial based in 16 UK and two Norwegian hospitals. The patients were assessed by a physiotherapist who independently completed the Lysholm on the same day.

RESULTS

Fit to the Rasch model was achieved [mean item fit -0.26, standard deviation (SD) 1.01] after removal of one item (Swelling). With no differential item functioning (DIF) by rater, the intraclass correlation coefficient was 0.9 [95% confidence interval (CI): 0.86-0.93] and a Bland-Altman plot showed no consistent difference in rating.

CONCLUSIONS

The Lysholm Knee Scale satisfies Rasch model expectations after removal of the swelling item. Generally there is a high degree of agreement between the patient and professional ratings. By removing the swelling item and using unweighted scores, a modified version of the Lysholm Knee Scale is recommended as an outcome measure for knee chondral damage.

Additional psychometric information and vision-specific questionnaires are available for age-related macular degeneration

PURPOSE

To present psychometric information and studies dealing with questionnaires for age-related macular degeneration (AMD) and visually impaired patients in addition to the study by Finger et al. "Quality of life in AMD: a review of available vision-specific psychometric tools". We propose that their literature search should not have focused solely on the specific eye disease AMD.

METHODS

The literature search was partly replicated (PubMed) by using "visual impairment" instead of "macular degeneration" as free text words. Psychometric information was obtained from the additional studies. Preliminary results from a differential item functioning (DIF) analysis used to examine the relationship between item responses on the Vision-related quality of life Core Measure (VCM1) of AMD patients versus patients with other eye conditions are discussed.

RESULTS

Eight studies of visually impaired patient populations, including AMD patients, are discussed, with psychometric information from six vision-specific questionnaires. The VCM1 items did not present DIF, which means that the items were equally interpreted by all patients.

CONCLUSIONS

The results on DIF and the additional studies presented here confirm that a specific eye disorder is of minor importance in the choice of a vision-specific questionnaire or, in this case, a literature search.

Evaluating clinical change and visual function concerns in drivers and nondrivers with glaucoma

PURPOSE

To compare drivers and nondrivers, and to describe the specific concerns of drivers, among individuals with glaucoma.

METHODS

Six hundred seven patients with newly diagnosed glaucoma treated at 14 clinical centers of the Collaborative Initial Glaucoma Treatment Study were randomly assigned to initial medicine or surgery and were followed up every 6 months. Driving status (drivers versus nondrivers) and patient-reported visual function were determined by the Visual Activities Questionnaire and the National Eye Institute Visual Function Questionnaire. Clinical evaluation included visual field mean deviation (MD) and visual acuity. Statistical comparisons were made using t, chi(2), and exact tests and regression and Rasch analyses.

RESULTS

Drivers were more likely than nondrivers to be male, white, married, employed, and more educated and to have higher incomes and fewer comorbidities. More than 50% of drivers reported at least "some" difficulty performing tasks involving glare, whereas 22% reported at least "some" difficulty with tasks requiring peripheral vision. At 54 months, drivers with moderate/severe bilateral visual field loss (VFL) reported greater difficulty with night driving and tasks involving visual search and visual processing speed than drivers with less bilateral VFL (all P<0.05). Although those who remained drivers over follow-up had better MD in both eyes than those who became nondrivers because of eyesight, a number of drivers had marked VFL.

CONCLUSIONS

Inquiring about specific difficulties with tasks related to glare, visual processing speed, visual search, and peripheral vision in driving, especially among patients with substantial bilateral visual field damage, will enable physicians to more effectively counsel patients regarding driving.

Outcome measures for research and clinical practice

This editorial provides a brief discussion of the importance of the selection and utilization of outcome measures in research and clinical practice.

Measuring low vision service outcomes: Rasch analysis of the seven-item National Eye Institute Visual Function Questionnaire

PURPOSE

To describe a short, functional visual disability instrument capable of measuring the outcomes of a government funded country-wide multicenter low vision service in Wales and to determine if postal implementation might lead to response bias.

METHODS

Seven items from the National Eye Institute Visual Function Questionnaire (NEI VFQ), which have previously been shown to be responsive to low vision service intervention, were incorporated into a postal questionnaire which was given to patients before they attended the all Wales Low Vision Service. Rasch analysis was used to describe the instrument's psychometric properties.

RESULTS

Rasch analysis of 490 completed questionnaires showed that all seven questions worked together to form a unidimensional scale. By combining the first two response categories, category utilization and targeting was improved. There were no significant differences in the age (p = 0.29), gender (p = 0.75), distance binocular Visual Acuity (VA; p = 0.86), living situation (p = 0.34) or prevalence of macular degeneration (p = 0.31) between those who returned a completed questionnaire and those who did not.

CONCLUSIONS

The seven-item National Eye Institute Visual Function Questionnaire is an appropriate and precise outcome measure that is acceptable to patients and easy to administer. It measures aspects of near, reading, and distance visual disability that have been shown to be amenable to low vision service provision and, therefore, it should be highly responsive to this intervention and facilitate inter-service assessment. We found no evidence to suggest that postal implementation results in response bias. The instrument is an appropriate measure of patient based outcomes for a large-scale, multicenter low vision service.