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.

C-reactive protein and retinal microvascular caliber in a multiethnic asian population

Retinal microvascular caliber is a risk marker for cardiovascular disease. The authors examined the relation between high-sensitivity C-reactive protein (hsCRP) and retinal microvascular caliber in a multiethnic Asian population (n = 3,583) of Chinese, Malays, and Indians aged 24-95 years residing in Singapore (2003-2007). Retinal arteriolar and venular diameters were measured and summarized as central retinal arteriolar equivalent (CRAE) and central retinal venular equivalent (CRVE), respectively. Persons with higher levels of hsCRP had wider CRVE (P(trend) < 0.001). In subgroup analysis stratified for different cardiovascular disease risk factors, the association between hsCRP and CRVE was seen in persons without diabetes (P(trend) < 0.001) but was absent in persons with diabetes (P(trend) = 0.200; P(interaction) = 0.004). No significant interaction between race/ethnicity and hsCRP in relation to retinal vascular caliber was observed. These data suggest that retinal venular caliber is associated with higher levels of hsCRP in Asians, which is consistent with studies in white Caucasian populations, further supporting the concept that retinal venular caliber may be a marker for low-grade systemic inflammation.

Sociodemographic, lifestyle, and medical risk factors for visual impairment in an urban asian population: the singapore malay eye study

OBJECTIVE

To describe the associations between sociodemographic, lifestyle, and medical risk factors and visual impairment in a Southeast Asian population.

METHODS

Population-based cross-sectional study of 3280 (78.7% response rate) Malay Singaporeans aged 40 to 80 years. Participants underwent a standardized interview, in which detailed sociodemographic histories were obtained, and clinical assessments for presenting and best-corrected visual acuity. Visual impairment (logMAR > 0.30) was classified as unilateral (1 eye impaired) or bilateral (both eyes impaired). Analyses used multivariate-adjusted multinomial logistic regression.

RESULTS

Older age and lack of formal education was associated with increased odds of both unilateral and bilateral visual impairment based on presenting and best-corrected visual acuity. The odds doubled for each decade older, and lower education increased the odds 1.59- to 2.83-fold. Bilateral visual impairment was associated with being unemployed (odds ratio [OR], 1.84; 95% confidence interval [CI], 1.30-2.60), widowed status (OR, 1.51; 95% CI, 1.13-2.01), and higher systolic blood pressure (OR, 1.96; 95% CI, 1.44-2.66). Diabetes was associated with unilateral (OR, 1.47; 95% CI, 1.10-1.95) and bilateral (OR, 1.69; 95% CI, 1.23-2.32) visual impairment using best-corrected visual acuity.

CONCLUSIONS

Older age, lower education, unemployment, being widowed, diabetes, and hypertension were independently associated with bilateral visual impairment. Public health interventions should be targeted to these at-risk populations.

Cataract surgery in high-risk age-related macular degeneration: a randomized controlled trial

BACKGROUND

To investigate if cataract surgery causes progression, from high-risk early age-related macular degeneration (AMD) to choroidal neovascularization (CNV), in the postoperative period.

METHODS

Randomized controlled trial. Patients, with visually significant cataract and fundus features of early AMD at high risk of progression to CNV, were randomized into two groups and were evaluated at baseline and 6 months. The study patients (n = 27) underwent immediate cataract surgery. The control group (n = 29) comprised patients who had cataract surgery deferred until after the 6-month visit. Assessment included visual acuity, quality of life (QoL) and fundus fluorescein angiography (FFA).

RESULTS

Of 68 eligible eyes, 60 participated and 56 completed the study. Three referred eyes (3.2%) were ineligible on the basis of a pre-existing, unsuspected occult CNV that was detected by baseline FFA. All three cases had end-stage exudative AMD in the fellow eye. Of the study eyes in the immediate surgery arm (n = 27), one (3.7%) developed CNV compared with none (0/29) in the deferred arm (chi(2); P = 1.0) at 6 months. In the operated group, there was a 2.8-line improvement in logMAR visual acuity and 2.1-fold average gain in QoL at 6 months.

CONCLUSIONS

No increased short-term risk of progression of AMD to CNV in high-risk fundi following uncomplicated phacoemulsification surgery was found. A low threshold for performing preoperative imaging in patients with AMD, especially in those with exudative AMD in the fellow eye, to exclude undetected CNV is recommended. Provided there is no CNV, there are distinct benefits of cataract surgery in people with early AMD.

Cataract symptom score questionnaire: Rasch revalidation

PURPOSE

The 5-item Cataract Symptom Score (CSS) was developed using classical test theory to determine appropriate timing for cataract surgery, its outcomes, and whether the symptoms included bother cataract patients. The purpose of this study was to investigate the psychometric properties of the 5-item CSS using Rasch analysis.

METHODS

Responses from 113 patients awaiting cataract surgery to the 5-item CSS (bothered by double or distorted vision, glare or halos, blurry vision, colors looking different and worsening of vision) were subjected to Rasch analysis. The use of response categories (threshold order), ability of CSS to discriminate between participants' severity of symptoms (person separation, recommended minimum value 2.0), matching of item difficulty to severity of symptoms (targeting), and ability of items to measure a single construct (unidimensionality) were investigated.

RESULTS

Participants used the response categories as intended. However person separation (1.74) was inadequate, suggesting that the CSS could differentiate only between two groups of participants by their symptoms. Furthermore the CSS was poorly targeted for our population, as the majority of our participants were not bothered by symptoms in the CSS. All items fit the single construct, implying that the CSS is a unidimensional measure of cataract symptoms.

CONCLUSIONS

The CSS is unable to discriminate people with cataract. This problem could be fixed by adding additional questions, but a superior approach may be to create an item bank of cataract symptoms questions, including those of the CSS, and utilize computer-adaptive testing for measurement.

Activities of Daily Vision Scale: what do the subscales measure?

PURPOSE

Previous Rasch analysis of the Activities of Daily Vision Scale (ADVS) did not address psychometric properties of its subscales or provide detailed assessment of dimensionality (whether the ADVS measures one or multiple constructs). This study was designed to examine these properties.

METHODS

Two hundred thirty-two participants (mean age, 74.2 years) awaiting cataract surgery self-administered the ADVS. Rasch analysis was used to assess the ADVS and its five subscales for unidimensionality (by principal components analysis, [PCA]), precision by person separation (discrimination between strata of participant ability), and targeting (matching of item difficulty to participant ability). Adequate person separation (minimum acceptable value, 2.0) is the fundamental requirement for measurement.

RESULTS

Only the near vision subscale had adequate measurement properties (person separation, 2.30). The entire ADVS showed a misfit to the Rasch model and lacked unidimensionality. PCA confirmed the presence of two additional traits-driving and glare disability-but neither possessed adequate person separation when assessed individually. Deleting these traits restored unidimensionality, but additional items misfit, necessitating item reduction. Finally, an eight-item ADVS-Near Vision Scale showed good fit and unidimensionality. Its contents were identical with the original near vision subscale. Targeting was suboptimal (2.30 logits).

CONCLUSIONS

Only one subscale, near vision, met the criteria for measurement. The revised eight-item ADVS-Near Vision subscale is a unidimensional measure of visual disability in cataract patients with mild visual disability. However, it is limited by measurement of near visual ability only. For more comprehensive measurement of visual disability, other questionnaires such as Catquest-9SF are preferable for cataract surgery outcomes assessment.

The Reliability of Data Collection Periods of Personal Costs Associated with Vision Impairment

PURPOSE

To determine the reliability of vision-related personal costs collected over 1, 3 and 6 months (extrapolated to 12 months) compared to one-year data.

METHODS

Participants of any age, with a presenting visual acuity of < 20/40 in the better eye and an ability to converse in English, were recruited. Monthly cost diaries, in large print and electronic copies with instructions available in audio and Braille, were used prospectively to collect personal costs. The personal expenses were grouped under four categories, namely: (a) medicines, products and equipment, (b) health and community services, (c) informal care and support and (d) other expenses. Sociodemographic and clinical data were also collected.

RESULTS

104 participants (59 females) with a mean age of 64 years completed the 12-months diaries. Almost 40% of the participants had severe visual impairment (< 20/200) in the better eye and the most common cause of vision loss was AMD (n=40; 38%). The mean total personal costs collected from the 12-months diaries were 3,330+/-2,887 AUS dollars. There were no significant differences between the 12-months data and extrapolated 1, 3 and 6-months diaries (t-tests; p=0.17, 0.89 and 0.73, respectively). However, the 1-month variation was substantially larger (SD+/-5,860) compared to the 3-month and 6-month variances (SD+/-3,037 and 3,030, respectively) for total costs. Also, compared to the 12-months diaries, the 1-month data consistently recorded the weakest correlation coefficients for all cost categories compared to the other time intervals.

CONCLUSIONS

Given that diary completion can be particularly challenging for individuals with impaired vision, a minimum 3-months data collection period can provide reliable estimates of annual costs associated with vision impairment.

The impact of corrected and uncorrected refractive error on visual functioning: the Singapore Malay Eye Study

PURPOSE

To determine the impact of corrected and uncorrected myopia and hyperopia on visual functioning in an urban Malay population.

METHODS

The Singapore Malay Eye Study is a population-based, cross-sectional study of Singaporean Malays aged 40 to 80 years. Myopia was defined as spherical equivalence (SE) <or= -0.50 D, hyperopia as SE > 1.0 D, and emmetropia as SE -0.5 to 1.0 D in the better eye. Uncorrected myopia and hyperopia were defined as at least a 2-line difference between habitual and best corrected VA in persons with myopia or hyperopia, respectively. Visual functioning was assessed with the VF-11 scale.

RESULTS

Of 2912 participants, 441 (15.1%) and 213 (7.3%) had corrected or uncorrected hyperopia and 333 (11.4%), and 131 (4.5%) had corrected or uncorrected myopia, respectively. Of those, 249 (8.6%) participants were considered emmetropic with a >2-line difference between habitual and best corrected vision, and 1543 (53.1%) participants had a <or=2-line difference. In linear regression models adjusted for age, sex, educational attainment, ocular conditions, and nonocular comorbidity, only uncorrected myopia was independently associated with poorer overall visual functioning (beta regression coefficient = -0.34; P <or= 0.001) and with activities such as reading street signs (beta = -0.47; 95% CI: -0.62 to -0.33; P < 0.001), recognizing friends (beta = -0.52; 95% CI: -0.67 to -0.37; P < 0.001), and watching television (beta = -0.33; 95% CI: -0.44 to -0.22; P < 0.001). These findings were replicated in a healthy subsample with no other eye conditions and nonocular comorbidities (n = 1112).

CONCLUSIONS

Adequate myopia correction can improve participation in daily living and visual functioning in people with myopia. Correction of hyperopia does not have this effect.

An evaluation of the reliability and validity of the visual functioning questionnaire (VF-11) using Rasch analysis in an Asian population

PURPOSE

To determine whether the VF-11 is a valid scale to measure visual functioning in an Asian population with vision impairment.

METHODS

Participants from the Singapore Malay Eye Study (SiMES) took part. Visual functioning was assessed by using the VF-11 (a modified version of VF-14 for an Asian population). Rasch analysis was performed on 618 participants with presenting visual acuity < 6/12 in the better eye.

RESULTS

Disordered thresholds were initially evident, indicating that the categories were difficult to discriminate and required category collapsing (from 5 to 4) for nine items. The removal of two misfit items related to driving resulted in a fit of the VF-9 data to the Rasch model (chi(2) = 50.5, df = 27, P = 0.005). There were no more misfit items. The person separation reliability value was 0.82 which demonstrates that the VF-9 has sufficient ability to discriminate between at least two groups of participants with different levels of visual functioning. The VF-9 significantly differentiated patients stratified by visual acuity demonstrating adequate criterion validity. All items were free of differential item functioning, and there was no evidence of multidimensionality. Targeting of person ability and item difficulty was suboptimal, although this is inevitable in a population-based survey where most people would not be disabled.

CONCLUSIONS

Although the Rasch-modified VF-9 scale achieved fit to the Rasch model, its suboptimal targeting suggests that the instrument does not have the range of items to assess the impact of vision impairment across the severity spectrum of vision loss in this population.

Impact of the severity of distance and near-vision impairment on depression and vision-specific quality of life in older people living in residential care

PURPOSE

To determine the relationship between the severity of distance and near-vision impairment on vision-specific quality of life (QoL) and depression in residential care residents.

METHODS

Residents from three low-level residential care facilities in Victoria (Australia) were recruited. All participants were assessed for cognitive impairment, distance and near-vision impairment (VI), and depression. Sociodemographic and other clinical data were also collected. The subscales of the Nursing Home Vision-Targeted Health-Related Quality-of-Life questionnaire (NHVQoL) were the main outcome measures and were validated by Rasch Analysis.

RESULTS

Seventy-six residents were enrolled. The mean +/- SD of the participants' age was 83.9 +/- 9.9 years, and most were women (n = 44; 60%); 46.4% (n = 35) had binocular presenting VI (<6/12), and 59% (n = 44) had at least mild near VI (worse than N8); 16% (n = 14) recorded depression symptoms, although depression was not associated with VI (P > 0.05). In linear regression models, distance and near VI was independently associated with poorer QoL on seven of the eight subscales of the NHVQoL scale (P < 0.05). The beta coefficients ranged from -12.3 to -80.2, which suggests that, on average, people with vision loss had poorer QoL, ranging between 12 and 80 points (scale range: 0-100) than did those with no VI. The QoL aspects most affected by vision loss were related to general vision, reading, hobbies, emotional well-being, and social interaction.

CONCLUSIONS

VI remains a major form of disability in individuals living in residential care facilities and affects vision-specific functioning and socioemotional aspects of daily living. A larger study is needed to confirm these findings.

Personal costs of visual impairment by different eye diseases and severity of visual loss

OBJECTIVES

To determine the personal out-of-pocket costs of visual impairment and to examine the expenditure pattern related to eye diseases and the severity of visual impairment.

METHODS

This prospective cohort study recruited participants of any age who were able to converse in English and had presenting visual acuity (VA) of < 6/12. Participants completed cost diaries regarding their daily personal vision-related expenditure. These were grouped under four categories: 1) medicines, products and equipment, 2) health and community services, 3) informal care and support and 4) other expenses. Socio-demographic and clinical data were also collected.

RESULTS

In 2003 150 participants, aged between 10 and 93 years old, were recruited. The median and mean total costs of visual impairment was Australian Dollars (AUD)$2416 and $3376, respectively (mode = AUD$2001-3000, SD +/- AUD$3050, Range AUD$7-$18610). Adjusting for age, there was no effect for severity of visual impairment (mild, moderate or severe) or type of eye diseases on the annual total personal out-of-pocket costs of visual impairment (p > 0.05).

CONCLUSIONS

Regardless of the type of eye diseases and the severity of visual loss, visual impairment posed a significant financial burden to both the individual and society.

An evaluation of the 10-item vision core measure 1 (VCM1) scale (the Core Module of the Vision-Related Quality of Life scale) using Rasch analysis

PURPOSE

To assess and re-engineer the Vision Core Measure 1 (VCM1) questionnaire in low vision (LV) and cataract participants using Rasch analysis.

METHODS

295 participants drawn from a low vision clinic and 181 from a cataract surgery waiting list completed the 10-item VCM1. Unidimensionality, item fit to the model, response category performance, differential item functioning (DIF) and targeting of items to patients were assessed. Category collapsing and item removal were considered to improve the questionnaire.

RESULTS

The initial fit of the VCM1 (combined populations) to the Rasch model showed lack of fit (chi2 = 83.3, df = 50, p = 0.002). There was evidence of DIF between the two populations which could not be resolved. Consequently, each population was assessed separately. Irrespective of the population, disordering of response category thresholds was evident. However, collapsing categories produced ordered thresholds and resulted in fit to the Rasch model for the LV (Total chi2 = 41.6, df = 30; p = 0.08) and cataract population (Total chi2 = 17.9, df = 20, p = 0.59). Overall, the VCM1 behaved as a unidimensional scale for each population and no item showed evidence of DIF. Item targeting to patients was however sub-optimal particularly for the cataract population.

CONCLUSION

The VCM1 questionnaire could be improved by shortening the response scale, although different response categories are required for cataract and LV populations. Calibration of items also differed across populations. While the VCM1 performs well within the Rasch model, in line with its initial purpose, it requires the addition of items to satisfactorily target low vision and cataract populations.

Visual impairment, causes of vision loss, and falls: the singapore malay eye study

PURPOSE

To report associations of visual impairment and the main causes of vision loss with falls in an older Asian population.

METHODS

The population-based Singapore Malay Eye Study examined 3280 (78.7% response rate) Malay adults 40 to 80 years of age. Details about any fall in the previous 12 months and personal and sociodemographic information were collected. Presenting visual acuity (PVA) was measured. Mild or moderate visual impairment (0.3 < logMar < 1.0), severe visual impairment (logMAR > or = 1.0), and the primary causes of visual impairment were determined by ophthalmologists at examination.

RESULTS

Of the 3280 participants, 3266 (99.6%) provided information about falls. Of these, 14.7% (n = 480) reported having fallen in the past 12 months. After adjustment for gender, age, body mass index, history of angina, heart attack, stroke, hypertension, diabetes, and self-rated health, the results showed that severe visual impairment in the worse eye significantly increased the risk of falling (60%; OR = 1.6; 95% CI 1.1 to 2.3). Severe visual impairment in one eye and mild or moderate visual impairment in the other also doubled the risk of falls (OR = 2.1; 95% CI 1.4-3.1). Having glaucoma (n = 21) increased the risk of falling by more than fourfold (OR = 4.2; 95% CI 1.2-12.3) after adjustment for visual acuity. Although mild or moderate visual impairment was not significantly associated with falls, odds ratios tended toward the direction of risk.

CONCLUSIONS

Findings from this Asian population provide further evidence in support of the association between severe visual impairment and falls in older persons.

Self-management programs for adults with low vision: needs and challenges

OBJECTIVE

To explore the needs of individuals with low vision in order to inform the contents of a low vision self-management (SM) program and determine potential barriers to participation.

METHODS

Semi-structured interviews were conducted with 48 participants with low vision resulting different from eye conditions. Qualitative analysis was conducted in order to identify major themes.

RESULTS

All participants described a range of consequences as a result of vision loss including difficulties with functional activities, social interaction and emotional distress. Less than half were interested in attending a SM program. Barriers included practical reasons as well as a perceived lack of need and unclear or negative perceptions of such a program.

CONCLUSION

SM programs for low vision are a promising way to help address the range of difficulties experienced by this population if barriers to participation can be overcome.

PRACTICE IMPLICATIONS

SM programs should include vision-specific strategies, training in generic problem-solving and goal setting skills and how to cope with emotional reactions to vision impairment. Programs should be delivered and promoted in such a way to enhance access and encourage uptake by those with a range of vision loss in the community.

Are Standard Instruments Valid for the Assessment of Quality of Life and Symptoms in Glaucoma?

PURPOSE

To determine if the impact of Visual Impairment Instrument (IVI) and Glaucoma Symptom Scale (GSS) are valid instruments to assess participation in daily living and ophthalmic complaints, respectively, in a glaucoma population.

METHODS

Patients with glaucoma were recruited from private and public clinics and completed the IVI and GSS questionnaires. The two scales were assessed for fit to the Rasch model. Unidimensionality, individual item and person fit to the model, response category performance (how respondents differentiate between the response options), differential item functioning (how subgroups, despite equal levels of the underlying trait, respond differently to an individual item), and targeting of items to patients (good spread of items across the full range of patients' scores) were assessed.

RESULTS

One hundred seventy-five participants (mean age = 71 year) were recruited. The majority (65%) had primary open angle glaucoma and good presenting visual acuity >or=6/9 in the better eye (87%). Only one-third of the participants had severe visual field loss in both eyes. Disordered thresholds were evident across all GSS items, indicating that the categories were difficult to discriminate and required category collapsing (5 to 3 categories). There was no evidence of person and item misfit, differential item functioning, and multidimensionality. However, both scales displayed ineffective person-item targeting as a large number of participants demonstrated little difficulty with the most difficult items.

CONCLUSIONS

Because of unsatisfactory targeting, The IVI and GSS are suboptimal scales to assess patients with glaucoma but relatively good vision. It is likely that items could be added to optimize the performance of both instruments. There may however be a need to develop a glaucoma-specific instrument to assess Quality of Life in this population.

Impact of Cataract Surgery on Quality of Life in Patients with Early Age-Related Macular Degeneration

PURPOSE

To investigate if cataract surgery improves overall and specific areas of quality of life (QoL) in patients with early age-related macular degeneration (AMD) using the impact of vision impairment (IVI) questionnaire.

METHODS

Patients with visually significant cataract and early AMD, who were being considered for cataract surgery in the study eye, were recruited. Eligible patients were randomized to either "early surgery" or "standard surgery" (standard cataract surgery waiting time of 6 months) groups. The IVI, sociodemographic, and clinical data were collected. Rasch analysis was used to estimate QoL person measures at baseline and follow-up. The data were analyzed using repeated measures ANOVA. Effect sizes were calculated using Cohen's d coefficient.

RESULTS

Fifty six patients (mean age = 78.5 years and visual acuity = 6/15) had one eye randomly allocated to either the early surgery (n = 29) or standard surgery (n = 27) groups. At follow-up, significant interaction effects were found for the overall IVI score [F(1,54) = 17.7; p < 0.001], the emotional well-being [F(1,54) = 13.4; p = 0.001], mobility and independence [F(1,54) = 13.4; p = 0.001], and reading and accessing information subscales [F(1,54) = 13.1; p = 0.001]. The standard surgery group systematically recorded worse scores at 6 months on all QoL measures whereas the early surgery group recorded significant gains (p < 0.001; Cohen's d = 0.66 to 0.91) on all of them. Visual acuity in the study eye significantly improved in the early surgery group only (Cohen's d = 1.1; p < 0.05) and improvement in log MAR lines read was identified as the single independent predictor of enhanced QoL explaining between 26 and 34% of the variance in the IVI scores.

CONCLUSIONS

Cataract surgery is justified in patients with early AMD. It brings significant improvements in visual acuity, aspects of daily living, and overall QoL.

The Effectiveness of Low-Vision Rehabilitation on Participation in Daily Living and Quality of Life

PURPOSE

To evaluate the effectiveness of a multidisciplinary low-vision rehabilitation program on quality of life evaluated by the Impact of Vision Impairment (IVI) instrument.

METHODS

First-time referrals to low-vision clinics were assessed before and after rehabilitation (3-6 months). Rasch analysis was used to estimate the three IVI subscale and overall values on an interval scale. A mixed between-within subjects ANOVA was used to identify whether presenting visual acuity had an interaction effect with rehabilitation change. Cohen d values were used to estimate the magnitude of the change and the standardized response mean (SRM) procedure was selected to determine the clinical significance of the rehabilitation-induced changes.

RESULTS

One hundred twenty-four women and 68 men (mean age, 80.3 years) completed the rehabilitation. Most had age-related macular degeneration (62%, 119) and were moderately to severely vision impaired (<6/18; 78%, 149). After rehabilitation, significant improvements were recorded for the overall IVI score (P = 0.006) and two subscales: reading and accessing information and emotional well-being (P = 0.007 and 0.009, respectively). No significant improvement was found on the mobility and independence subscale (P = 0.07). The magnitude of the post-intervention improvement was found to be relatively moderate (Cohen d = 0.17-0.30) and clinically modest (SRM = 0.22-0.42).

CONCLUSIONS

Significant improvements in overall quality of life and two specific areas of daily living in people with low vision were found, although the magnitude and clinical significance of the rehabilitation-induced gains were modest. Further investigation in other models of low-vision rehabilitation is needed to optimize quality of life gains in people with low vision.

The Impact of Vision Impairment Questionnaire: An Assessment of Its Domain Structure Using Confirmatory Factor Analysis and Rasch Analysis

PURPOSE

To assess and validate the subscale structure of the 28-item Impact of Visual Impairment (IVI) Scale by using confirmatory factor analysis (CFA) and Rasch analysis for use as an outcome measure.

METHODS

Three hundred nineteen participants completed the IVI questionnaire, and the responses then were subjected to Rasch analysis by RUMM2020 software. With the person estimates for each item, CFA was used to assess two hypothesized structures: three-and four-factor models. The subscales of the model with the best fit were then further validated by Rasch analysis.

RESULTS

CFA supported a three-factor model that included items from the emotional well-being, reading and accessing information, and mobility and independence subscales. Almost all the selected goodness-of-fit statistics for the three-factor model were better than the recommended values. The factor loadings of the items on their respective domains were all statistically significant (P < 0.001) and ranged between 0.54 and 0.81. The three subscales individually fitted the Rasch model according to the item-trait interaction test (mobility and independence chi(2) [df] = 45.9 [44], P = 0.39; emotional well-being = 28.4 [32], P = 0.65; and reading and accessing information = 43.5 [36], P = 0.18). The item-fit residuals values of the three subscales were <2.5 and showed mean and standard deviations approximating 0 and 1, respectively. The internal consistency reliability of the subscales (alpha) was substantial, ranging between 0.89 and 0.91.

CONCLUSIONS

An examination of the IVI dimension confirmed a three-subscale structure that displays interval measurement characteristics likely to provide a valid and reliable assessment of restriction of participation. The findings provide an opportunity for a more detailed measurement of the effects of different types of low-vision rehabilitation programs.

The Impact of Vision Impairment Questionnaire: An Evaluation of Its Measurement Properties using Rasch Analysis

PURPOSE

To explore the psychometric properties of the Impact of Vision Impairment scale (IVI) by using Rasch analysis.

METHODS

Three hundred fourteen first-time referrals to low-vision clinics completed the 32-item IVI. The data were Rasch-analyzed with a partial credit model using RUMM2020 software (RUMM Laboratory, Perth, WA, Australia). The overall fit of the model, response scale, individual item fit, differential item functioning, unidimensionality, and person-separation reliability were assessed.

RESULTS

Initially, 26 items displayed disordered thresholds. However, collapsing the response scale to three categories (4 items) and four categories (28 items) produced ordered response thresholds for all items. Four items with high proportions of missing responses, poor spread, high skewness, and deviation between observed and expected model curves were then removed. This adjustment produced overall fit to the Rasch model (item-trait interaction chi(2) = 118.3; P = 0.32). The final mean (SD) person and item fit residuals ere 0.06 (0.85) and -0.20 (1.45), respectively. The person-separation reliability was 0.9, indicating that the scale was able to discriminate between several different groups of participants. The revised scale was well targeted to the participants, with similar mean locations for items (0.00) and persons (0.16). A significant difference between participants of mild, moderate, and severe visual impairment (ANOVA; P 0.001) supported the criterion validity of the Rasch-scaled IVI.

CONCLUSIONS

The results provide support for the measurement properties of the Rasch-scaled 28-item version of the IVI and of its potential for assessing outcomes of low-vision rehabilitation. A raw score-to-Rasch person measure conversion is supplied.

Impact of age related macular degeneration on quality of life

AIMS

To describe the impact of age related macular degeneration (AMD) on quality of life and explore the association with vision, health, and demographic variables.

METHODS

Adult participants diagnosed with AMD and with impaired vision (visual acuity <6/12) were assessed with the Impact of Vision Impairment (IVI) questionnaire. Participants rated the extent that vision restricted participation in activities affecting quality of life and completed the Short Form General Health Survey (SF-12) and a sociodemographic questionnaire.

RESULTS

The mean age of the 106 participants (66% female) was 83.6 years (range 64-98). One quarter had mild vision impairment, (VA<6/12-6/18) and 75% had moderate or severely impaired vision. Participants reported from at least "a little" concern on 23 of the 32 IVI items including reading, emotional health, mobility, and participation in relevant activities. Those with mild and moderate vision impairment were similarly affected but significantly different from those with severe vision loss (p<0.05). Distance vision was associated with IVI scores but not age, sex, or duration of vision loss.

CONCLUSION

AMD affects many quality of life related activities and not just those related to reading. Referral to low vision care services should be considered for people with mild vision loss and worse.

The Agreement between the Heidelberg Retina Tomograph and a Digital Nonmydriatic Retinal Camera in Assessing Area Cup-to-Disc Ratio

PURPOSE

To determine the repeatability and agreement between a digital camera (monoscopic and stereoscopic images) and the Heidelberg Retina Tomograph (HRT; Heidelberg Engineering, Heidelberg, Germany) in determining cup-to-disc ratio. A secondary purpose was to determine the monoscopic and stereoscopic thresholds that maximize specificity and sensitivity when compared with the HRT.

METHODS

Community living participants aged between 70 and 79 years had their optic discs imaged with a digital nonmydriatic retinal camera (NMRC) and the HRT. Intraclass correlation coefficients (ICCs) and 95% tolerance limits of change were used to determine repeatability characteristics of the instruments. The agreement between the HRT- and NMRC-derived area cup-to-disc ratios was assessed using weighted kappa statistics and receiver operator characteristic (ROC) curves.

RESULTS

The agreements between the monoscopic and stereoscopic images and HRT were assessed for 1238 and 1173 eyes, respectively. The reliability measures for both NMRC techniques and HRT were almost perfect (ICC = 0.84-0.99) with narrow tolerance limits of change (9.2%-18.4%) and very small systemic biases (P < 0.05). The agreement between the HRT and both NMRC techniques was substantial, with a weighted kappa = 0.83. The HRT gave a marginally larger area cup-to-disc ratio than the monoscopic and stereoscopic images by 0.008 and 0.006, respectively (P < 0.001). The areas under the ROC curves for both NMRC techniques were 0.98, indicating excellent discriminating characteristics (P < 0.001). An area cup-to-disc ratio cutoff of > or =0.5 for the monoscopic and stereoscopic NMRC was highly specific (94.1% and 91.6%) and sensitive (87.5% and 97.2%, respectively) in determining an HRT-derived area cup-to-disc ratio >0.6.

CONCLUSIONS

The monoscopic and stereoscopic digital images showed excellent repeatability and demonstrated substantial agreement with the HRT. The results indicate that the digital NMRC could be a reliable and useful instrument for assessing area cup-to-disc ratio and screening for glaucoma-suspect eyes in the community.

Assessment of optic disc cupping with digital fundus photographs

PURPOSE

To determine the agreement between the assessment of retinal digital images by using an overlay transparency sheet and the Heidelberg retinal tomograph (HRT) in determining cup-disk ratios greater than 0.6.

DESIGN

Diagnostic test comparison.

METHODS

Computerized topographic and monoscopic digital images of the optic disk of 628 people aged 70 to 79 years were assessed. A grader (M.C.) defined the disk margin on HRT images, and the operation software computed the area cup-disk ratio. The same grader also determined whether the vertical cup-disk ratio on retinal images was greater than 0.6 by superimposing a transparency overlay sheet over the images. Findings of a second grader (J.G.F.) were used to establish reliability measures.

RESULTS

The intragrader reliability for the overlay method and HRT was almost perfect (intraclass correlation coefficient [ICC] = 0.96 and 0.99, respectively), whereas the intergrader reliability was good (ICC = 0.77 and 0.92, respectively). A perfect agreement was found on 28 (85%) of 33 eyes between the overlay and HRT methods in determining cup-disk ratios greater than 0.6.

CONCLUSIONS

The overlay transparency method appears to be a reliable and promising alternative in determining cup-disk ratios greater than 0.6 in a community screening setting.

Detecting cataract causing visual impairment using a nonmydriatic fundus camera

PURPOSE

To assess the validity of a digital nonmydriatic fundus camera in detecting cataract as a cause of visual impairment.

DESIGN

Diagnostic test comparison.

METHODS

Photos of the anterior segment of 72 eyes were taken with a nonmydriatic fundus camera and assessed for cataract by two graders. Dilated biomicroscopy examination of the anterior segment of the same 72 eyes was then performed and cataract graded using the Wilmer scale.

RESULTS

Grader 1 and 2 reported 90% and 94% sensitivity and 82% and 77% specificity, respectively, when the digital photos were compared with slit-lamp biomicroscopy in determining visually significant cataract. In addition, both graders showed similar substantial agreement between the digital photos and slit-lamp biomicroscopy when assessed for cataract (unweighted kappa 0.87 and 0.92, respectively, for graders 1 and 2).

CONCLUSION

The nonmydriatic fundus camera may be an alternative method for screening for visually significant cataract in the community.

The determinants of participation in activities of daily living in people with impaired vision

PURPOSE

To investigate the determinants of participation in daily activities in people with impaired vision using the Impact of Vision Impairment (IVI) instrument.

DESIGN

Cross-sectional study.

METHODS

We recruited 319 participants with no vision rehabilitation history, distance visual acuity (VA) <6/12 (better eye), the ability to converse in English, and 18 years or older. Participants completed the 32-item IVI questionnaire and provided demographic, personal, cultural, and environmental details on vision-related functioning. Visual acuity data were either abstracted from the participants' files or assessed by qualified personnel. Participants also completed the SF-12 to evaluate physical (PCS-12) and mental health (MCS-12).

RESULTS

The areas of greatest restriction of participation were associated with reading, outdoor mobility, participation in leisure activities, and shopping. In stepwise linear regression presenting VA, the PCS-12 and MCS-12 explained the variance in leisure and work (60 participants or 19%), consumer and social interaction (92 participants or 30%), household and personal care (76 participants or 24%), mobility (92 participants or 30%), emotional reaction to visual loss and (106 participants or 33%), and total IVI score (114 participants or 36%). Having age-related macular degeneration contributed marginally to the IVI domains and total score (P <.05-.01), except for the emotional domain. Belonging to a social group explained 3% and 2% of the variance in the consumer and social interaction and emotional domains, respectively (P <.05).

CONCLUSIONS

Distance VA and physical and mental health explained more than a third of the variance of the total score, suggesting that an intervention aimed at improving quality of life may include strategies to improve not only vision-related rehabilitation but also mental and physical health.

The impact of diabetic retinopathy on participation in daily living

OBJECTIVE

To determine the restriction of participation in daily activities of people with diabetic retinopathy using the Impact of Vision Impairment questionnaire.

METHODS

Individuals with diabetic retinopathy and a visual acuity (VA) worse than 20/40 or 6/12 in the better eye were eligible. Participants answered demographic questions and had VA information abstracted from medical records. If VA information was unavailable, it was assessed by an orthoptist.

MAIN OUTCOME MEASURES

All participants completed the Impact of Vision Impairment questionnaire, which was either self-administered or interviewer administered. The physical and mental health components were assessed using the Medical Outcomes Study 12-Item Short Form (SF-12) questionnaire.

RESULTS

Forty-five participants (mean age, 67.5 years) were recruited, with almost 70% (30/45) recording a VA worse than 20/60 or 6/18 in the better eye. The median duration of vision loss was 2.0 years. The highest restriction was reported for the Leisure and Work, Mobility, and Consumer and Social Interaction domains (mean, 3.0, 2.8, and 2.8, respectively), compared with the Emotional Reaction to Visual Loss and Household and Personal Care domains (mean, 2.3 and 2.1, respectively) (P<.005). The activities with the greatest restriction of participation were reading print, mobility, work, and leisure. A poorer VA in the better eye correlated independently with increased restriction of participation, as measured by the Impact of Vision Impairment questionnaire scores (partial correlations, 0.29-0.41; P< or =.03).

CONCLUSION

Low-vision rehabilitation services aiming to improve outdoor mobility, print reading, participation in leisure activities, and psychological health may be an effective strategy to help people with diabetic retinopathy increase their participation in daily activities.

Barriers to accessing low vision services

AIM

To investigate barriers to accessing low vision services in Australia.

METHODS

Adults with a vision impairment (<6/12 in the better eye and/or significant visual field defect), who were current patients at the Royal Victorian Eye and Ear Hospital (RVEEH), were interviewed. The questions investigated self-perceived vision difficulties, duration of vision loss and satisfaction with vision and also examined issues of awareness of low vision services and referral to services. Focus groups were also conducted with vision impaired (<6/12 in the better eye) patients from the RVEEH, listeners of the Radio for the Print Handicapped and peer workers at Vision Australia Foundation. The discussions were recorded and transcribed.

RESULTS

The questionnaire revealed that referral to low vision services was associated with a greater degree of vision loss (p = 0.002) and a greater self-perception of low vision (p = 0.005) but that referral was not associated with satisfaction (p = 0.144) or difficulties related to vision (p = 0.169). Participants with mild and moderate vision impairment each reported similar levels of difficulties with daily activities and satisfaction with their vision (p > 0.05). However, there was a significant difference in the level of difficulties experienced with daily activities between those with mild-moderate and severe vision impairment (p < 0.05). The participants of the focus groups identified barriers to accessing low vision services related to awareness of services among the general public and eye care professionals, understanding of low vision and the services available, acceptance of low vision, the referral process, and transport.

CONCLUSION

In addition to the expected difficulties with lack of awareness of services by people with low vision, many people do not understand what the services provide and do not identify themselves as having low vision. Knowledge of these barriers, from the perspective of people with low vision, can now be used to guide the development and content of future health-promotion campaigns.

The relationship between lower body strength and obstructed gait in community-dwelling older adults

OBJECTIVES

To determine the relationship between lower body strength of community-dwelling older adults and the time to negotiate obstructed gait tasks.

DESIGN

A correlational study.

SETTING

The Biomechanics Laboratory, Deakin University, Australia.

PARTICIPANTS

Twenty-nine women and 16 men aged 62 to 88 were recruited using advertisements placed in local newspapers. The participants were independent community dwellers, healthy and functionally mobile.

MEASUREMENTS

Maximal isometric strength of the knee extensors and dynamic strength of the hip extensors, hip flexors, hip adductors, hip abductors, knee extensors, knee flexors, and ankle plantar flexors were assessed. The times to negotiate four obstructed gait tasks at three progressively challenging levels on an obstacle course and to complete the course were recorded. The relationship between strength and the crossing times was explored using linear regression models.

RESULTS

Significant associations between the seven strength measures and the times to negotiate each gait task and to walk the entire course at each level were obtained (r = -0.38 to -0.55; P < .05). In addition, the percentage of the variance explained by strength (R(2)), consistently increased as a function of the progressively challenging level. This increase was particularly marked for the stepping over task (R(2) = 19.3%, 25.0%, and 27.2%, for levels 1, 2, and 3, respectively) and the raised surface condition (R2 = 17.1%, 21.1%, and 30.8%, for levels 1, 2, and 3, respectively).

CONCLUSION

The findings of the study showed that strength is a critical requirement for obstructed locomotion. That the magnitude of the association increased as a function of the challenging levels suggests that intervention programs aimed at improving strength would potentially be effective in helping community-dwelling older adults negotiate environmental gait challenges.

Differences in the neuromuscular capacity and lean muscle tissue in old and older community-dwelling adults

BACKGROUND

This study investigated whether there was a worsening of the neuromuscular capacity of older adults after the seventh decade of life.

METHODS

Fifteen healthy community-dwelling old (< 70 years of age) and 15 older adults (> or = 70 years of age) were assessed for maximal isometric strength (MVC) and force production characteristics, a one-repetition maximum (1-RM) performance, electromyographic (EMG) activity, and bone-free lean tissue (BFLT) mass of the lower extremity.

RESULTS

The isometric MVC, 1-RM, and BFLT mass values in the old group were significantly greater than in the older group. In addition, the individual BFLT mass values correlated significantly with the isometric MVC values (r = .85) and the 1-RM scores of the thigh muscle groups (r = .54-.80). The old group generated significantly greater isometric maximal rate of torque development than the older group and performed significantly better at all intervals of the absolute and relative force-time curves. The voluntary muscle activation of the knee extensors of the old group produced significantly higher integrated EMG (iEMG) activity at each epoch in the early iEMG-time curve compared with the old group.

CONCLUSIONS

The results suggest that the age-related deterioration in maximal strength measures and rapid force production characteristics in older adults could be related to a reduction in the mass and neural activation of the thigh muscles. The deterioration of the neuromuscular system of community-dwelling older adults may contribute to an increased difficulty in performing daily activities and may increase their risks of tripping and falling.