Manjula Marella

The Psychometric Validity of the NEI VFQ-25 for Use in a Low-Vision Population

PURPOSE To determine the psychometric validity of the National Eye Institute-Visual Function Questionnaire (NEI VFQ-25) and its subscale structure for use in people with low vision. METHODS Two hundred thirty-two participants completed the NEI VFQ-25. Rasch analysis was used to test the psychometric performance of the questionnaire and each subscale. Factor models were hypothesized and tested with confirmatory factor analysis (CFA) and subsequently validated with Rasch analysis. RESULTS For the overall scale, two rating scales had to be dichotomized and three misfitting items removed to improve fit to the Rasch model. There was evidence of multidimensionality, indicating that the scale would benefit from scale splitting. For the NEI VFQ-25 subscale structure, six of the original 12 subscales could not fit the Rasch model because of item insufficiency (fewer than two items) and the remaining six displayed poor item fit characteristics indicating that the NEI VFQ-25 does not have a viable subscale structure. CFA supported a two-factor model with visual functioning (10 items) and socioemotional (9 items) scales. Most goodness-of-fit statistics were within the recommended range of values. The factor loadings of items on their respective scales were statistically significant (P < 0.001) and ranged between 0.59 and 0.84. The two scales individually fitted the Rasch model and were found to be unidimensional with adequate psychometric characteristics. CONCLUSIONS The native NEI VFQ-25 is a better performing instrument when split into visual functioning and socioemotional scales. These scales possess valid parameters for assessment of the impact of low vision in this population.

Vision-Specific Distress and Depressive Symptoms in People with Vision Impairment

PURPOSE To determine the unique contribution of vision-specific distress in predicting depressive symptoms in people with vision impairment attending a tertiary eye care clinic. METHODS In this cross-sectional study, interview-administered surveys were conducted with 143 adult patients who had presenting visual acuity <0.3 logMAR. Depressive symptoms were assessed with the Patient Health Questionnaire-9 and vision-specific distress was assessed with the Impact of Vision Impairment (IVI) Questionnaire emotional well-being subscale. In addition, level of restriction of participation in common daily activities due to vision impairment was assessed with the IVI and measures of general physical health and social support were included. RESULTS Twenty-one (14.7%) of 143 participants reported clinically significant depressive symptoms and an additional 27.3% (n = 39) had mild depressive symptoms. Vision-specific distress was the strongest unique predictor of depressive symptoms (beta = 0.37, P < 0.001), with physical health (beta = -0.22, P < 0.01), age (beta = -0.18, P < 0.05), and experience of a negative life event (beta = 0.15, P < 0.05) also contributing significantly to depressive symptoms. Results also indicated that vision-specific distress mediates the impact of participation restriction due to vision impairment on depressive symptoms. CONCLUSIONS An assessment of vision-specific distress may be a useful tool with which to identify those at risk of depression or in need of early intervention in eye care or rehabilitation settings. Depression treatment approaches or depression prevention strategies for people with vision impairment may benefit from a focus on vision-specific distress.

The Impact of Vision Impairment for Children (IVI_C): validation of a vision-specific pediatric quality-of-life questionnaire using Rasch analysis.

PURPOSE To validate the Impact of Vision Impairment for Children (the IVI_C), a new vision-specific pediatric instrument designed to assess the affect of impaired vision on quality of life (QoL) in children. METHODS The IVI_C was administered to vision-impaired and normally sighted students, 8 to 18 years of age. Reliability and validity were tested, and the IVI_C was subjected to Rasch analysis to assess the scale unidimensionality, measurement characteristics, response options, and targeting. RESULTS The mean (SD) presenting bilateral distance visual acuity (VA) for the vision-impaired group (n = 122) was 1.10 (0.79) logMAR and 1.15 (0.80) logMAR for near VA. After the initial response categories were collapsed from five to three, content validity was further supported by good person and item fit parameters. The person separation index (PSI) was 0.85, which indicates that the IVI_C can assess QoL across children of several participation levels. The scale was shown to be unidimensional after principal components analysis (PCA) of the residuals (t-test; P = 0.48, P = 0.34). Significant differences in overall person measures between the vision-impaired and normally sighted groups substantiated the scale discriminant validity (ANOVA; F = 78.75; P < 0.0001). Guttman split-half correlations for temporal, mode (face-to-face and telephone), and interobserver administrations were 0.95, 0.90, and 0.86, respectively, supporting scale reliability. CONCLUSIONS The modified IVI_C is a unidimensional, reliable, and valid scale for assessing QoL of children with vision impairment. It provides a valid means of assessing the outcomes of interventions and needs in children with vision impairment.

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.

Rasch Analysis Reveals Problems with Multiplicative Scoring in the Macular Disease Quality of Life Questionnaire

PURPOSE To evaluate validity and psychometric characteristics of the Macular Disease Quality of Life questionnaire (MacDQoL), a multiplicative rating scale designed to measure vision-related quality of life (VRQoL) in macular diseases and age-related macular degeneration (AMD). DESIGN Cross-sectional study. PARTICIPANTS We included 108 patients with neovascular AMD at baseline before ranibizumab treatment. METHODS The psychometric properties of the MacDQoL were assessed using Rasch analysis, exploring key indices such as response category functioning, instrument unidimensionality, discriminant ability, and targeting of item difficulty to patient ability. MAIN OUTCOME MEASURES Measurement characteristics of the MacDQoL. RESULTS In the MacDQoLs native form, the majority of response categories were underutilized and thresholds disordered. This could not be remedied without eliminating the importance ratings owing to the ambiguous nature of the response categories. Scaling problems were resolved by using the impairment rating scale only and collapsing response categories to 4. However, the MacDQoL was multidimensional, necessitating the omission of a number of items and splitting it into an activity limitation and mobility and a socioemotional well-being scale. This improved the psychometric parameters of the revised MacDQoL, although no correlation with clinical measures such as visual acuity was found. CONCLUSIONS The multiplicative rating scale of the MacDQoL is flawed and does not provide scientific measurement of VRQoL. Measurement can be restored with a series of revisions to the instrument. This study reinforces the importance of considering rating scale design when choosing patient reported outcomes instruments for healthcare research.

The Longitudinal Impact of Macular Telangiectasia (MacTel) Type 2 on Vision-Related Quality of Life

PURPOSE To determine the longitudinal impact of idiopathic macular telangiectasia (MacTel) type 2 on vision-specific quality of life (QoL). METHODS Participants with MacTel type 2 and controls with no vision impairment were recruited at baseline. All underwent a full ophthalmic examination and the interview-administered 28-item Impact of Vision Impairment (IVI) questionnaire at baseline, to gather information on sociodemographic factors and vision-specific QoL. The MacTel patients were reassessed at 24 months. RESULTS For the MacTel participants (n = 22), the median (range) age and visual acuity were 64 years (45-87) and 20/32 (20/13-20/63) in the better eye, respectively. The corresponding median values in the control group (n = 38) were 57 years (41-68) and 20/25 or better in both eyes, respectively. Rasch analysis showed that the IVI and its three subscales had sufficient psychometric validity and possessed interval level estimates. The control group had almost twice the level of vision-specific QoL than did the MacTel group at baseline on all IVI scores (P < 0.001 for all). At 24 months, we found no significant change in any of the IVI scores in the MacTel group. Similarly, there was no significant difference in visual acuity in the better or worse eyes in that group after 2 years. CONCLUSIONS Persons with MacTel type 2 had poorer overall vision-related QoL than did healthy controls. Several aspects of vision-related QoL and distance visual acuity did not significantly change after 24 months. Longer follow-up assessment periods are needed to determine the longitudinal impact of this condition on vision-related QoL.

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

ObjectiveTo 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).MethodsVRQoL 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.ResultsFollowing 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.ConclusionsVision 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.

Field-testing of the rapid assessment of disability questionnaire.

BackgroundThe Rapid Assessment of Disability (RAD) questionnaire measures the magnitude and impact of disability and aims to inform the design of disability inclusive development programs. This paper reports the psychometric evaluation of the RAD.MethodsThe initial version of the RAD comprised five sections: 1) demographics, 2) functioning, 3) rights awareness, 4) well-being, and 5) access to the community. Item functioning and construct validity were assessed in a population-based study in Bangladesh. Data were analysed using descriptive statistics (sections 2 and 5) and Rasch modelling (sections 3 and 4). A subsequent case–control study in Fiji tested the refined questionnaire in a cross-cultural setting and assessed the sensitivity and specificity of the RAD section 2 to identify people with disability.Results2,057 adults took part in the study (1,855 in Bangladesh and 202 in Fiji). The prevalence of disability estimated using RAD section 2 in Bangladesh was 10.5% (95% CI 8.8-12.2), with satisfactory sensitivity and specificity (62.4% and 81.2%, respectively). Section 3 exhibited multidimensionality and poor differentiation between levels of rights awareness in both Bangladesh (person separation index [PSI] = 0.71) and Fiji (PSI = 0.0), and was unable to distinguish between people with and without disability (Bangladesh p = 0.786, Fiji p = 0.403). This section was subsequently removed from the questionnaire pending re-development. Section 4 had good ability to differentiate between levels of well-being (PSI = 0.82). In both countries, people with disability had significantly worse well-being scores than people without disability (p < 0.001) and also access to all sectors of community except legal assistance, drinking water and toilets (p < 0.001).ConclusionsFiled-testing in Bangladesh and Fiji confirmed the psychometric robustness of functioning, well-being, and community access sections of the RAD. Information from the questionnaire can be used to inform and evaluate disability inclusive development programs.

Validation and Reliability of the VF-14 Questionnaire in a German Population

PURPOSE To evaluate the validity, reliability, and measurement characteristics of the Visual Function 14 (VF-14) in a German sample using Rasch analysis. METHODS This was a clinic-based, cross-sectional study with 184 patients with low vision recruited from an outpatient clinic at a German eye hospital. Participants underwent a clinical examination and completed the German VF-14 scale. The validity of the VF-14 scale was assessed using Rasch analysis. The main outcome measure was the overall functional score provided by the VF-14. RESULTS After collapsing two response categories for items 13 and 14, the VF-14 scale satisfied fundamental criteria to achieve fit to the Rasch model, namely, ordered thresholds, the ability to distinguish between different strata of participant ability, absence of misfitting items, no evidence of unidimensionality, and no significant differential item functioning for key sociodemographic covariates. The VF-14 is able to discriminate between participants with different levels of vision impairment and across different cultural groups. CONCLUSIONS The VF-14 is a valid, reliable, and unidimensional questionnaire for use in a German population. These findings contribute to the growing evidence base for second generation patient reported outcome measures in ophthalmology, and support the use of the German VF-14 in tertiary eye clinics in Germany to capture the impact of visual impairment on visual function from the patients perspective and to inform low vision rehabilitation and interventions.

A randomised controlled trial of a self-management programme for low vision implemented in low vision rehabilitation services ☆

OBJECTIVE To investigate the effectiveness of a low vision self-management programme (LVSMP) in older adults. METHODS Participants (n=153) were existing clients of a national low vision rehabilitation organisation randomly allocated to usual services (n=60) or usual services plus LVSMP (n=93). The LVSMP was an 8-week group programme facilitated by low vision counsellors. The primary outcome was vision-specific quality of life (QoL) measured using the Impact of Vision Impairment (IVI) questionnaire. Secondary outcomes emotional well-being, self-efficacy and adaptation to vision loss were measured using the depression, anxiety, stress scale (DASS), general self-efficacy scale (GSES), and short form adaptation to age-related vision loss scale (AVL12). RESULTS At one and six month follow-up assessments, no significant between-group differences were found for vision-specific QoL, emotional well-being, adaptation to vision loss or self-efficacy (p>0.05). Univariate and multivariate analyses revealed no impact of the intervention on outcome measures. CONCLUSIONS In contrast to previous work, our study found limited benefit of a LVSM programme on QoL for older adults accessing low vision services. PRACTICE IMPLICATIONS When implementing self-management programmes in low vision rehabilitation settings, issues of client interest, divergence of need, programme accessibility and fidelity of intervention delivery need to be addressed.