Likert and Guttman scaling of visual function rating scale questionnaires

PURPOSE

To test the assumptions underlying Likert scoring of visual function questionnaires.

METHODS

Questionnaires were administered to 284 low-vision subjects by telephone. Each subject was administered two of four questionnaires: ADVS, NEI VFQ-25 plus supplement, expanded VAQ, and VF-14.

RESULTS

Z-scores for cumulative frequency of using each rating category across subjects are not linear with rating category rank and items are not the same difficulty for any of the questionnaires. Guttmann coefficients of reproducibility ranged from 57% for the ADVS to 51% for the NEI VFQ-25. Cronbach alphas ranged from 0.92 for the VF-14 to 0.96 for the NEI VFQ; however, inter-item consistency coefficients ranged from 0.24 for the VAQ to 0.45 for the NEI VFQ. Likert scores were significantly correlated between instruments, ranging from 0.66 for NEI VFQ vs ADVS to 0.90 for the VF-14 vs. ADVS.

CONCLUSIONS

The rating scales of all four questionnaires fail to satisfy Likert's assumptions. Also, ratings are probabilistic, rather than deterministic, which means that the Likert model is not valid for these questionnaires. However, Likert scores for all four instruments are intercorrelated, suggesting that they are monotonic with the latent subject trait distributed in the low vision sample.

What do Different Visual Function Questionnaires Measure?

PURPOSE

There are dozens of visual function questionnaires (VFQs). VFQs differ in number of items, item content, and response categories. Despite differences, all VFQs are designed to measure vision-related functional ability in visually impaired people. The objective is to determine whether four popular VFQs measure the same variable in visually impaired patients.

METHODS

Two of four VFQs (ADVS, NEI-VFQ, VF-14, VAQ) plus the SF-36 were administered by telephone to 407 consecutive low vision clinic patients. Thus, each instrument was administered to just over 200 patients, and there were over 67 patients for each of the 6 pairings of VFQs. Separate Rasch analyses were performed on patient responses to each VFQ and to the physical and mental health domains in the SF-36.

RESULTS

Person measure estimates from the four VFQs were highly correlated. Person measures estimated from the mental health and physical domains of the SF-36 were uncorrelated with each other and with person measures estimated from the VFQs. From principal components analysis we concluded that three factors were necessary and sufficient: the first principal component accounts for 62% of the variance, the other two factors account for 16% and 14% of the variance, respectively. The VFQs load most heavily on the first factor; the mental health component of the SF-36 loads most heavily on the second; and the physical limitations component of the SF-36 loads most heavily on the third.

CONCLUSIONS

The four VFQs measure the same vision-related functional ability variable in low vision patients that is separate from and independent of the physical and mental health variables measured by the SF-36.

Economic evaluation of blind rehabilitation for veterans with macular diseases in the Department of Veterans Affairs

PURPOSE

The Department of Veterans Affairs (VA) Low Vision Intervention Trial (LOVIT) developed an outpatient low-vision programme for patients with macular diseases providing low-vision rehabilitation comparable to VA inpatient blind rehabilitation centres (BRCs). This programme targets veterans who do not need or chose not to participate in a comprehensive inpatient blind rehabilitation programme. We examined costs and consequences using veterans in LOVIT and comparable veterans in an inpatient BRC.

METHODS

We compared costs and consequences between treatment patients who participated in LOVIT, a two-site randomized clinical trial, and a sample of comparable patients who received treatment at a VA inpatient BRC. We measured consequences as the change in functional visual ability from baseline to follow-up (LOVIT: 4 months after randomization; BRC: 3 months after discharge) using the VA Low Vision Visual Functioning Questionnaire (VA LV VFQ-48).

RESULTS

There were 55 LOVIT and 121 BRC patients for our analyses. Average costs were $38,627.3 higher for BRC patients ($5,054.4 +/- $404.7 SD for LOVIT vs. $43,681.7 +/- $8,853.6 SD for BRC, p < 0.0001). Thus, the BRC cost $38,627.3 per patient more than the LOVIT programme (95% CI: $17,414 to $273,482). There was a greater improvement in overall visual ability, mobility, and visual motor skill scores for BRC patients; however, there was no significant difference in improvement in reading ability or visual information processing scores.

CONCLUSIONS

As VA increases outpatient blind rehabilitation services, LOVIT provides a model for expanding outpatient low-vision rehabilitation services for veterans at substantially lower costs than current inpatient BRC services.

Self-reported importance and difficulty of driving in a low-vision clinic population

PURPOSE

To validate estimates of self-perceived driving ability from difficulty ratings of driving tasks and to determine the association of the importance and difficulty of driving with the magnitude of visual impairments.

METHODS

A consecutive series of 851 patients at a low-vision clinic rated the importance of driving on a four-point scale. Those who gave nonzero importance ratings then rated driving difficulty on a five-point scale. Those who gave nonzero difficulty ratings then rated the difficulty of each of 21 driving tasks on a five-point scale. Visual acuity was measured with the Early Treatment of Diabetic Retinopathy Study (ETDRS) chart, and contrast sensitivity was measured with the Pelli-Robson chart. Rasch analysis was used to test the validity and reliability of self-perceived driving ability estimates from difficulty ratings of tasks.

RESULTS

Patients who rated driving as not important (41%) had worse visual acuity (logMAR = 0.88) and worse contrast sensitivity (log CS = 0.83) than did those who rated driving as extremely important (55%; logMAR = 0.62; log CS =1.03; multivariate analysis of variance [MANOVA]; P = 0.003). Self-perceived driving ability correlated negatively with the overall rating of driving difficulty (r = -0.69; P < 0.001) and with logMAR (r = -0.28; P < 0.001), and correlated positively with log CS (r = 0.35; P < 0.001). The most difficult driving tasks were navigating in parking ramps, parking in the correct space, seeing lane markings, and reading signs. The least-difficult driving tasks were seeing traffic and reading the speedometer. Rasch analysis confirmed instrument validity and reliability.

CONCLUSIONS

Low-vision patients appeared to devalue the goal of driving when visual impairments were more severe. Valid measures of self-perceived driving ability can be estimated from difficulty ratings of specific driving tasks.

The Activity Inventory: an adaptive visual function questionnaire

PURPOSE

The Activity Inventory (AI) is an adaptive visual function questionnaire that consists of 459 Tasks nested under 50 Goals that in turn are nested under three Objectives. Visually impaired patients are asked to rate the importance of each Goal, the difficulty of Goals that have at least some importance, and the difficulty of Tasks that serve Goals that have both some importance and some difficulty. Consequently, each patient responds to an individually tailored set of questions that provides both a functional history and the data needed to estimate the patient's visual ability. The purpose of the present article is to test the hypothesis that all combinations of items in the AI, and by extension all visual function questionnaires, measure the same visual ability variable.

METHODS

The AI was administered to 1880 consecutively-recruited low vision patients before their first visit to the low vision rehabilitation service. Of this group, 407 were also administered two other visual function questionnaires randomly chosen from among the Activities of Daily Living Scale (ADVS), National Eye Institute Visual Functioning Questionnaire (NEI VFQ), 14-item Visual Functioning Index (VF-14), and Visual Activities Questionnaire (VAQ). Rasch analyses were performed on the responses to each VFQ, on all responses to the AI, and on responses to various subsets of items from the AI.

RESULTS

The pattern of fit statistics for AI item and person measures suggested that the estimated visual ability variable is not unidimensional. Reading-related and other items requiring high visual resolution had smaller residual errors than expected and mobility-related items had larger residual errors than expected. The pattern of person measure residual errors could not be explained by the disorder diagnosis. When items were grouped into subsets representing four visual function domains (reading, mobility, visual motor, visual information), and separate person measures were estimated for each domain as well as for all items combined, visual ability was observed to be equivalent to the first principal component and accounted for 79% of the variance. However, confirmatory factor analysis showed that visual ability is a composite variable with at least two factors: one upon which mobility loads most heavily and the other upon which reading loads most heavily. These two factors can account for the pattern of residual errors. High product moment and intraclass correlations were observed when comparing different subsets of items within the AI and when comparing different VFQs.

CONCLUSIONS

Visual ability is a composite variable with two factors; one most heavily influences reading function and the other most heavily influences mobility function. Subsets of items within the AI and different VFQs all measure the same visual ability variable.

Is there a standard of care for eccentric viewing training?

A study was conducted to determine the current Department of Veterans Affairs (VA) standard of practice for eccentric viewing (EV) training. EV training is the process of teaching patients to realign the visual image away from a diseased foveal/macular region onto healthier retina. Optometrists and Visual Skills Instructors at all VA blind rehabilitation centers (BRCs) and VICTORS (vision impairment centers to optimize remaining sight) programs were asked to rate preference for EV prescription criteria, evaluation, and training techniques. Responses were received from 70% of BRCs and 67% of VICTORS. The respondents reported that all programs include EV training. The average minutes of training per patient varied from 20 minutes to nearly 24 hours, with instructors within a single center varying by as much as two orders of magnitude. Routinely, 82% of optometrists prescribe EV training, yet no consensus was found among these practitioners as to the criteria for selecting the best EV area. The results of this survey reveal an inconsistent standard of practice across VA centers and demonstrate the need for prospective studies of the efficacy, effectiveness, and cost-effectiveness of EV training.

Using the VA LV VFQ-48 and LV VFQ-20 in Low Vision Rehabilitation

PURPOSE

This study was conducted to demonstrate use of a simple scoring algorithm for the 48-item Veterans Affairs Low Vision Visual Functioning Questionnaire (VA LV VFQ-48) that approximates the measure of persons' visual ability that would be calculated with Rasch analysis and to provide a short form version of the questionnaire for clinical practice and outcomes research.

METHODS

Items were eliminated from the VA LV VFQ-48 to reduce redundancy and shorten the instrument. The approximation of persons' visual ability calculated with the scoring algorithm for vision function questionnaires developed by Massof was compared with the person measure estimated from Rasch analysis for a sample of 126 subjects entering a low vision rehabilitation program.

RESULTS

The approximation captures 98% of the variability in the Rasch measure estimate of persons' visual ability and 97% of the variability in the change score estimate. The relationship does not hold in circumstances where patients with high visual ability find most items to be easy. A 20-item short form of the instrument was constructed for use in low vision service delivery.

CONCLUSIONS

The scoring algorithm can be used with the VA LV VFQ-48 or short form versions of the questionnaire. Clinicians can use the algorithm to score the VA LV VFQ from examination of individual patients or as an outcome measure for their low vision rehabilitation programs. Research investigators can use the scoring algorithm with small samples when Rasch analysis is not reliable or in studies where Rasch analysis is not practical. Rasch analysis is still recommended for research studies that require more accurate assessments.

An Interval-Scaled Scoring Algorithm for Visual Function Questionnaires

PURPOSE

The primary purpose of the study is to present and test a simple algorithm for scoring visual function questionnaires (VFQs) that approximates person measure estimates from Rasch analysis, does not introduce nonlinearities at extreme scores, and is insensitive to missing data. A secondary purpose is to test the hypothesis that all VFQs measure the same visual ability variable and can be calibrated to a common measurement scale.

METHODS

Each of 407 consecutively recruited low vision patients were administered two of four visual function questionnaires: Activities of Daily Living Scale (ADVS), National Eye Institute Visual Functioning Questionnaire (NEI VFQ), 14-item Visual Functioning Index (VF-14), Visual Activities Questionnaire (VAQ). Separate Rasch analyses, using the Andrich rating scale model, were performed on responses to each of the four VFQs and again on the merged data of all instruments. An approximation of visual ability, based on average functional reserve and an inverse hyperbolic tangent transformation, is presented and tested by comparing visual ability estimates from the Rasch analyses to corresponding estimates from the approximations.

RESULTS

Relative to person measure estimates from Rasch analysis, the approximations were observed to be linear and highly reliable (intraclass correlations ranged from 0.97 to 0.997). The measurement scale of each of the four instruments was observed to be a linear transformation of the measurement scale estimated from the merged responses of all four instruments. The approximation algorithm transforms rating scale responses for each instrument to a common measurement scale. By randomly censuring item responses for each subject, it was demonstrated that the approximation algorithm is robust and insensitive to missing data.

CONCLUSIONS

A simple scoring algorithm based on an inverse hyperbolic tangent transformation of average functional reserve produces highly reliable approximations of visual ability estimated from Rasch analysis for the ADVS, NEI VFQ, VAQ, and VF-14. All four instruments measure the same visual ability variable in units that can be calibrated to a common measurement scale.

Natural course of visual field loss in patients with Type 2 Usher syndrome

PURPOSE

To evaluate the natural course of visual field loss in patients with Type 2 Usher syndrome and different patterns of visual field loss.

METHODS

Fifty-eight patients with Type 2 Usher syndrome who had at least three visual field measurements during a period of at least 3 years were studied. Kinetic visual fields measured on a standard calibrated Goldmann perimeter with II4e and V4e targets were analyzed. The visual field areas in both eyes were determined by planimetry with the use of a digitalizing tablet and computer software and expressed in square inches. The data for each visual field area measurement were transformed to a natural log unit. Using a mixed model regression analysis, values for the half-life of field loss (time during which half of the remaining field area is lost) were estimated. Three different patterns of visual field loss were identified, and the half-life time for each pattern of loss was calculated.

RESULTS

Of the 58 patients, 11 were classified as having pattern type I, 12 with pattern type II, and 14 with pattern type III. Of 21 patients whose visual field loss was so advanced that they could not be classified, 15 showed only a small residual central field (Group A) and 6 showed a residual central field with a peripheral island (Group B). The average half-life times varied between 3.85 and 7.37 for the II4e test target and 4.59 to 6.42 for the V4e target. There was no statistically significant difference in the half-life times between the various patterns of field loss or for the test targets.

CONCLUSION

The average half-life times for visual field loss in patients with Usher syndrome Type 2 were statistically similar among those patients with different patterns of visual field loss. These findings will be useful for counseling patients with Type 2 Usher syndrome as to their prognosis for anticipated visual field loss.

Short- and Long-Term Effects of an Intensive Inpatient Vision Rehabilitation Program

OBJECTIVE

To assess the effects of a visual rehabilitation program on visually impaired subjects' visual ability and ability to perform activities.

DESIGN

Prospective observational study.

SETTING

Telephone interviews of respondents in their homes the week before admission to the rehabilitation center and 3 months and 1 year after discharge from the rehabilitation center.

PARTICIPANTS

A total of 178 consecutive patients from the Hines Blind Rehabilitation Center participated in development of the 48-item Veterans Affairs Low Vision Visual Functioning Questionnaire (VA LV VFQ-48). Data were analyzed for 95 who participated in all 3 administrations of the questionnaire.

INTERVENTION

Comprehensive blind rehabilitation program (mean hospital admission, 40 d).

MAIN OUTCOME MEASURE

The self-report ratings of patients' difficulty performing 48 activities on the VA LV VFQ-48.

RESULTS

The increase in visual ability +/- standard deviation of .981+/-.482 logits (equivalent to an 8-line improvement in visual acuity on an Early Treatment of Diabetic Retinopathy Study chart) at 3 months postrehabilitation decreased to .682+/-.485 logits (equivalent to a loss of 2.5 lines of visual acuity on the same chart) 1 year postrehabilitation. The effect sizes measured at 3 months (2.035) and 1 year (1.495) indicate large treatment effects corresponding to statistically significant differences for the increase in visual ability at 3 months and 1 year postrehabilitation (paired 2-tailed t tests, P<.001) relative to pretreatment measures. The difference in visual abilities measured at 3 months and 1 year posttreatment also is statistically significant (P<.001).

CONCLUSIONS

Treatment effects decreased over the 12-month follow-up period. However, the group of patients whose data were analyzed was still statistically and clinically significantly better at their 1-year follow-up than before beginning treatment.

Measuring Outcomes of Vision Rehabilitation with the Veterans Affairs Low Vision Visual Functioning Questionnaire

PURPOSE

To evaluate the sensitivity to change, in patients who undergo vision rehabilitation, of the Veteran Affairs (VA) Low Vision Visual Functioning Questionnaire (LV VFQ-48), which was designed to measure the difficulty visually impaired persons have in performing daily activities and to evaluate vision rehabilitation outcomes.

METHODS

Before and after rehabilitation, the VA LV VFQ-48 was administered by telephone interview to subjects from five sites in the VA and private sector. Visual acuity of these subjects ranged from near normal to total blindness.

RESULTS

The VA LV VFQ exhibited significant differential item functioning (DIF) for 7 of 48 items (two mobility tasks, four reading tasks, and one distance-vision task). However, the DIF was small relative to baseline changes in item difficulty for all items. Therefore, the data were reanalyzed with the constraint that item difficulties do not change with rehabilitation, which assigns all changes to the person measure. Subjects in the inpatient Blind Rehabilitation Center (BRC) program showed the largest changes in person measures after vision rehabilitation (effect size = 1.9; t-test P < 0.0001). The subjects in the outpatient programs exhibited smaller changes in person measures after rehabilitation (effect size = 0.29; t-test P < 0.01). There was no significant change in person measures for the control group (test-retest before rehabilitation).

CONCLUSIONS

In addition to being a valid and reliable measure of visual ability, the VA LV VFQ-48 is a sensitive measure of changes that occur in visual ability as a result of vision rehabilitation. Patients' self-reports of the difficulty they experience performing daily activities measured with this instrument can be used to compute a single number, the person measure that can serve as an outcome measure in clinical studies. The VA LV VFQ-48 can be used to compare programs that offer different levels of intervention and serve patients across the continuum of vision loss.

Timing and directions for administration of questionnaires affect outcomes measurement

We used data from two pilot studies to compare the change in patients' self-reported health-related quality of life after participation in two nearly identical Department of Veterans Affairs (VA) Blind Rehabilitation Center (BRC) programs, the Southwestern BRC in Tucson, Arizona, and the BRC at the VA hospital in Hines, Illinois. Researchers at the Southwestern BRC administered the National Eye Institute Visual Functioning Questionnaire as directed by the developer. Researchers at the Hines BRC modified the directions to consider use of low-vision devices. Interval person-ability and item-difficulty measures estimated from patient responses pre- and postrehabilitation were compared with these same measures obtained at follow-up. At the Southwestern BRC, no change was reported in either person or item measures 3 months after rehabilitation. At the Hines BRC, improvement was seen in both the person and item measures when measurements were made immediately following rehabilitation. Because a temporary halo effect may explain the higher ratings at discharge, veterans from the Hines cohort were contacted by telephone and administered the same instrument 3 years later. For these subjects, the improvement noted in the person measure disappeared at follow-up, while the improvement in the item measure was maintained.

Application of stochastic measurement models to visual function rating scale questionnaires

PURPOSE

To test hypotheses that low vision patient responses to visual function rating scale questionnaires conform to an additive conjoint structure and that the Likert score is a sufficient statistic for the latent patient trait; to compare results for two competing stochastic measurement models; and to determine if different questionnaires measure the same construct in low vision patients.

METHODS

Visual function rating scale questionnaires were administered to 284 low vision subjects by telephone. Each subject was administered two of four questionnaires: ADVS, NEI VFQ-25 plus supplement, expanded VAQ, and VF-14.

RESULTS

Data were analyzed with the Muraki item response model and the Andrich measurement model. The estimates of latent person, item, and response threshold measures from the two models are linearly related. The Muraki model produced a better overall fit to the item response data, the Andrich model produced a better fit to the average ratings for each person and item. Fit statistics for the Andrich model were proportional to the item-dependent discrimination parameter in the Muraki model. The ADVS was the most accurate measure and the NEI VFQ was the least. Reliability was similar for all four instruments. Person measures for each pair of instruments were linearly related indicating that all four instruments measured the same construct. The person measure estimate from the Andrich model is monotonic with the average rating. That relationship suggests a transformation of the Likert score that can correct the floor and ceiling effects in rating scale data.

CONCLUSIONS

Patient responses to all four questionnaires conform to varying degrees to an additive conjoint structure. The Likert score is a sufficient statistic for the ADVS and the VAQ, but not for the NEI VFQ or VF-14. All four instruments measure the same construct in the low vision population, but they differ in measurement accuracy and precision.

Visual Disability Variables. II: The Difficulty of Tasks for a Sample of Low-Vision Patients

OBJECTIVES

To test the validity and reliability of measures of visual ability and to evaluate the relation between measurements made at the task level and measurements made at the goal level of a hierarchical model for visual disability.

DESIGN

Validation of a telephone-administered functional assessment instrument using Rasch analysis on self-assessment ratings.

SETTING

Telephone interviews of respondents in their homes.

PARTICIPANTS

Consecutive series of 600 outpatients with low vision.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Ordinal ratings of the difficulty in performing a subset of 337 tasks. Measures of the visual ability of each patient and the required visual ability to perform each task were made using the Andrich rating scale model. Measurement validity and reliability were tested statistically by comparing response patterns and distributions to measurement model expectations.

RESULTS

Results were consistent with a single visual ability construct. Patients' visual ability estimated from task difficulty ratings agreed with estimates from goal difficulty ratings ( r =.74); the difficulty of individual goals was equal to the weighted average of the difficulties of subsidiary tasks ( r =.79). However, conclusions from the Rasch analysis were not confirmed by principal components analysis of item residuals, which indicated that visual ability had a 2-dimensional structure, with 1 factor related to mobility and the other related to reading. Factor analysis on person measures estimated from subsets of functionally grouped items confirmed the 2-dimensional structure of visual ability.

CONCLUSIONS

Our study results confirm the hierarchical structure of the Activity Breakdown Structure model and show how the individualized Activity Inventory can produce measures of limitations in functional vision.

Visual Disability Variables. I: The Importance and Difficulty of Activity Goals for a Sample of Low-Vision Patients

OBJECTIVE

To test the validity and reliability of latent trait measures estimated from ratings by low-vision patients of the importance and difficulty of selected activity goals.

DESIGN

Validation of a telephone-administered functional assessment instrument using Rasch analysis of self-assessment ratings.

SETTING

Telephone interviews of respondents in their homes. Participants Consecutive series of 600 outpatients with low vision.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Ratings of the importance and difficulty of achieving 41 activity goals. Person and item traits were measured with the Andrich rating scale model. Measurement validity and reliability were tested statistically by comparing response patterns and distributions with measurement model expectations.

RESULTS

Patients could distinguish only 3 categories of importance and 4 categories of difficulty. The distributions of person and item measure fit statistics were consistent with 2 unidimensional constructs: value of independence estimated from importance ratings and visual ability estimated from difficulty ratings. However, 8 of 41 activity goals were poor estimators of value of independence and 7 of 41 activity goals were poor estimators of visual ability. Person measure distributions could be divided into 3 statistically distinct strata for estimates from both importance ratings and difficulty ratings. Item measure distributions could be divided into 21 strata for estimates from importance ratings and 7 strata for estimates from difficulty ratings.

CONCLUSIONS

The 2 variables that define visual disability-value of independence and visual ability-are valid constructs that can be estimated accurately and reliably from patient ratings of the importance and difficulty of activity goals.

Psychometric Properties of the Veterans Affairs Low-Vision Visual Functioning Questionnaire

PURPOSE

To describe psychometric properties of a self-report questionnaire, the Veterans Affairs (VA) Low-Vision Visual Functioning Questionnaire (LV VFQ-48), which was designed to measure the difficulty visually impaired persons have performing daily activities and to evaluate low-vision outcomes.

METHODS

The VA LV VFQ-48 was administered by telephone interview to subjects with visual acuity ranging from near normal to total blindness at five sites in the VA and private sector. Rasch analysis with the Andrich rating scale model was applied to difficulty ratings from 367 subjects, to evaluate measurement properties of the instrument.

RESULTS

High intercenter correlations for item measure estimates (intraclass correlation coefficient [ICC]=0.97) justified pooling the data from these sites. The person measure fit statistics (mean square residuals) confirm that the data fit the assumptions of the model. The item measure fit statistics indicate that responses to 19% of the items were confounded by factors other than visual ability. The separation reliabilities for pooled data (0.94 for persons and 0.98 for items) demonstrate that the estimated measures discriminate persons and items well along the visual ability dimension. ICCs for test-retest data (0.98 for items and 0.84 for persons) confirm temporal stability. Subjects used the rating categories in the same way at all five centers. Ratings of slight and moderate difficulty were used interchangeably, suggesting that the instrument could be modified to a 4-point scale including not difficult, slightly/moderately difficult, extremely difficult, and impossible. Fifty additional subjects were administered the questionnaire with a 4-point scale to confirm that the scale was used in the same way when there were four rather than five difficulty ratings.

CONCLUSIONS

The VA LV VFQ-48 is valid and reliable and has the range and precision necessary to measure visual ability of low-vision patients with moderate to severe vision loss across diverse clinical settings.

Use of Rasch person-item map in exploratory data analysis: A clinical perspective

The National Institutes of Health (NIH) includes visual impairment in the 10 most prevalent causes of disability in America. As rehabilitation programs have the potential to restore independence and improve the quality of life for affected persons, NIH research priorities include evaluating their effectiveness. This paper demonstrates a clinical perspective on the use of the Rasch person-item map to evaluate the range and precision of a new vision function questionnaire in early analysis (prior to full sample). A self-report questionnaire was developed to measure the difficulty that persons with different levels of vision loss have performing daily activities. This 48-item Veterans Affairs Low-Vision Visual Functioning Questionnaire (VA LV VFQ-48) was administered to 117 low-vision patients. Preliminary analysis indicates that the questionnaire items are applicable to persons of differing abilities. The Rasch person-item map demonstrates that the field-test version of the VA LV VFQ-48 has good range and is well centered with respect to the person measure distribution. Construct validity and reliability are also demonstrated.

Measuring the severity of stress urinary incontinence using the Incontinence Impact Questionnaire

AIMS

Questionnaires, including the Incontinence Impact Questionnaire (IIQ), have been used to assess the severity of urinary incontinence in clinical trials. However, the summed score derived from the IIQ does not have any inherent clinical meaning. Also, a summed score does not have interval properties, complicating the interpretation of changes in severity. The purpose of this study is to test the hypothesis that incontinence-related disability is a measurable variable and that the IIQ can measure that variable accurately.

METHODS

We used Rasch analysis, a logistic regression technique, to estimate an interval scale of incontinence severity. Rasch analysis is based on the mathematical assumption that each subject's response to any given item is a function of (a) the individual's inherent level of disability and (b) the inherent difficulty of that item.

RESULTS

Twenty-seven women with urodynamic stress urinary incontinence (USUI) completed the IIQ. Using Rasch analysis, we found that women with USUI had the most difficulty engaging in "physical recreational activities" and the least difficulty participating in "relationship with family." We also assessed the ability of the IIQ to discriminate between individuals with respect to disease severity. We found that most of the items in the IIQ are useful for discriminating incontinence severity among women with mild or moderate incontinence, but very few IIQ items distinguish among women with severe incontinence.

CONCLUSIONS

Our results have important implications for clinical trials using the IIQ: among women treated for severe incontinence, the standard IIQ summed score will underestimate the magnitude of any change in incontinence severity.

Measuring low-vision rehabilitation outcomes with the NEI VFQ-25

PURPOSE

To evaluate the sensitivity of the National Eye Institute Visual Functioning Questionnaire-25 (NEI VFQ-25) to change in visual abilities after low-vision rehabilitation in two different Veterans Administration (VA) low-vision programs

METHODS

Seventy-seven legally blind veterans from the Blind Rehabilitation Center (BRC) at Hines VA Hospital and 51 partially sighted veterans from the Visual Impairment Center to Optimize Remaining Sight (VICTORS) program at the Chicago Health Care Network, West Side Division, were administered the NEI VFQ-25 plus supplement in interview format at admission and discharge. Instructions for administration were modified to have study participants answer all the questions as if they were wearing glasses or contact lenses or were using low-vision devices. Interval measures of person ability and item difficulty were estimated from the patients' responses to 34 of the 39 items on the VFQ-25 plus supplement before and after rehabilitation, by the polytomous rating scale measurement model of Wright and Masters.

RESULTS

In VICTORS patients, item order by difficulty before rehabilitation agreed with item order for BRC patients. Visual ability scales are used similarly by different patients with different degrees of low vision. Based on prerehabilitation person measure distributions, VICTORS patients were less disabled, as would be predicted by visual acuity, than were BRC patients. After rehabilitation, estimated item difficulty for 4 of the 34 items decreased significantly in both BRC and VICTORS patients.

CONCLUSIONS

The present study demonstrates that the NEI VFQ-25 plus supplement can be used to measure the effects of low-vision rehabilitation; however, only 7 of the 34 items tested are sensitive to change after rehabilitation. Targeted activities, such as reading ordinary print, small print, and street signs are easier to perform for graduates of both programs after rehabilitation. The patients' visual ability also shows improvement in both BRC and VICTORS. Improvement in visual ability is independent of change in difficulty of targeted items. Although this was not a controlled clinical trial, the decrease in difficulty of targeted items may reflect the use of low-vision aids and training to make tasks easier. The change in visual ability may reflect positive outcomes of rehabilitation or may be the consequence of patients' overestimates of their functional ability at the time of discharge.

A self-assessment instrument designed for measuring independent mobility in RP patients: generalizability to glaucoma patients

PURPOSE

To determine whether the patient-based assessment of difficulty in mobility, developed and validated in a group of patients with retinitis pigmentosa (RP), is valid for measuring perceived visual ability for independent mobility in patients with glaucoma.

METHODS

A mobility questionnaire that had previously been developed was administered to 83 patient-volunteers who had various amounts of visual impairment caused by glaucoma. Each volunteer rated the perceived difficulty of walking independently in each of 35 mobility situations. A Rasch analysis of the ordinal difficulty ratings was used to estimate interval measures of perceived visual ability for independent mobility.

RESULTS

The instrument showed good construct and content validity and high reliability scores. Criterion validity of the instrument was demonstrated by its ability to discriminate mobility-related behaviors such as fear of falling, asking for accompaniment, and believing their ability to travel independently is less than that of persons with normal vision. To make the perceived mobility scale comparable for the two diagnostic groups the questionnaire was restricted to those items whose difference in item-logit distributions was within +/-3 (18 items). Using the same instrument calibration, we compared the person measures between the patients with glaucoma and those with RP. Patients with glaucoma had, on average, higher perceived visual ability for independent mobility than those with RP.

CONCLUSIONS

The instrument developed for patients with RP, to determine difficulty across a range of mobility situations, is a valid measure of perceived ability for independent mobility in patients with glaucoma.

Grating visual acuity using the preferential-looking method in elderly nursing home residents

PURPOSE

To assess the performance of two approaches to visual acuity testing in a group of nursing home residents with cognitive impairment. The study was a cross-sectional comparison of the effectiveness of two tests of visual acuity.

METHODS

Nursing home residents participating in a clinical trial were tested with both recognition acuity charts and grating acuity cards (Teller) by masked observers.

RESULTS

Of the nursing home residents (n = 656) who participated in the study, 86% could respond to visual acuity testing in at least one eye. Eighty-four percent were testable using Teller cards versus 73% who were testable by Early-Treatment Diabetic Retinopathy Study (ETDRS) charts or Lea symbol charts. Forty-one percent of individuals with MiniMental Status Examination (MMSE) scores lower than 10 were testable by recognition acuity, whereas 61% were testable with grating acuity cards. Grating acuity correlated well with recognition acuity (R = 0.79; 95% CI, 0.75-0.98, intraclass correlation coefficient [ICC]). The correlation was slightly lower in individuals with decreased MMSE scores. Although grating acuity was one line better than recognition acuity on average and median acuities were the same, 24% of individuals had results that differed by three or more lines.

CONCLUSIONS

Teller acuity cards can effectively test the vision in cognitively impaired individuals who are not testable by conventional means. Grating acuity results correlated well with those of recognition acuity, although differences of three or more lines were not uncommon. Wider use of grating acuity testing allows a more complete assessment of visual function in the cognitively impaired elderly.

The measurement of vision disability

The American Medical Association's (AMA) visual efficiency scale, a vision disability metric based on visual impairment measurements, was adopted in 1925. That scale was based on a 30-year history of theoretical models in vision economics, a misinterpretation of Snellen notation for visual acuity, and an erroneous application of Weber's psychophysical law. The AMA visual efficiency scale survived uncontested for 75 years. In 2001, the AMA adopted a new vision disability scale based on logarithmic transformations of visual acuity and visual field diameter. Like the earlier visual efficiency scale, the new scale is theoretical-it is not supported by any data that speak to the relationship between vision disability and visual impairments. Attempts to measure vision disability date to the early 1980s with the development of self-assessment visual function rating scale questionnaires. Nearly all of the questionnaires developed over the last 20 years use Likert scales, but use them incorrectly. The development of a vision disability metric based on Likert scaling parallels the historical development of other forms of measurement. A tutorial review of psychometrics-classical test theory, item response theory, and Rasch analysis-shows how vision disability measurement scales can be estimated from Likert-type visual function rating scales. We conclude that preliminary data relating measures of vision disability to measures of visual acuity and visual fields support the new AMA vision disability scale.

A model of the prevalence and incidence of low vision and blindness among adults in the U.S

Population-based vision screening studies of the prevalence rate of low vision and blindness in the U.S. are reviewed to evaluate the sources of disagreement among studies. The major reasons that studies disagree on prevalence rate estimates are differences in best-corrected visual acuity criteria for low vision and differences in the age range of the oldest age category. When corrections are made for these differences, the results of all prevalence rate studies, except the Mud Creek Valley Study, fit the same prevalence rate vs. age function. The greater prevalence rate of low vision and blindness for each age category that was observed in the Mud Creek Valley Study can be attributed to the higher prevalence rate of cataract associated with a paucity of health care services in the Mud Creek Valley population. The time-derivative of the prevalence rate vs. age function fit to the data provided an estimate of the annual incidence rate of low vision and blindness vs. age. The estimated annual incidence agreed with estimates from unpublished 8-year incidence data of the Baltimore Eye Survey. The incidence rate of low vision and blindness for Americans aged 40 to 60 years is higher among blacks than among whites. For Americans greater than age 60 years, the incidence rate for whites exceeds that for blacks. This observation probably reflects the different natural histories of glaucoma, a leading cause of low vision and blindness among black Americans, and age-related macular degeneration, a leading cause of low vision and blindness among white Americans. Using the age-dependent models of prevalence rate of low vision and blindness for white and black populations, an estimated 1.5 million Americans over age 45 years have a best-corrected visual acuity in the better eye that is < or = 20/70. Based on the incidence rate estimates, approximately 240,000 new cases of low vision and blindness occur each year. With the aging of the U.S. population, that number is expected to double over the next 25 years.

Visual function assessment questionnaires

With increased emphasis on functional outcomes in ophthalmology, third-party health care payers and research funding agencies have turned their attention to the development and use of visual function questionnaires. Since 1980, more than a dozen such self-report visual function questionnaires have been developed. All of these instruments include items that ask about specific daily activities; patients must respond with a rating that represents the level of difficulty that they experience with the activity described. This article reviews all of the known instruments, with special attention paid to their validity and reliability. Most validation studies have reported high response consistency across items and significant correlations of instrument scores with visual impairment measures. Only two studies have measured test-retest reliability. The developers of visual function questionnaires typically divide the items into several different subscales, suggesting that different variables are being measured. Although the items are very similar for the different instruments, there is little agreement among instruments on the definition of subscales. All instruments are scored as the average of the ordinal patient ratings across items for each subscale and/or for the total instrument. Measurement issues underlying the scoring of ordinal patient ratings are discussed. It is argued that unless the instruments can be converted to interval scales, the averaging of patient ratings does not yield true measurements. The three visual function questionnaires that were calibrated with a statistical item response model, which estimates interval scales, are reviewed. It is concluded that future research and development should devote additional attention to the measurement properties of functional assessment instruments.