Jan Mitchell

Psychometric evaluation of the MacDQoL individualised measure of the impact of macular degeneration on quality of life

BackgroundThe MacDQoL is an individualised measure of the impact of macular degeneration (MD) on quality of life (QoL). There is preliminary evidence of its psychometric properties and sensitivity to severity of MD. The aim of this study was to carry out further psychometric evaluation with a larger sample and investigate the measures sensitivity to MD severity.MethodsPatients with MD (n = 156: 99 women, 57 men, mean age 79 ± 13 years), recruited from eye clinics (one NHS, one private) completed the MacDQoL by telephone interview and later underwent a clinic vision assessment including near and distance visual acuity (VA), comfortable near VA, contrast sensitivity, colour recognition, recovery from glare and presence or absence of distortion or scotoma in the central 10° of the visual field.ResultsThe completion rate for the MacDQoL items was 99.8%. Of the 26 items, three were dropped from the measure due to redundancy. A fourth was retained in the questionnaire but excluded when computing the scale score. Principal components analysis and Cronbachs alpha (0.944) supported combining the remaining 22 items in a single scale. Lower MacDQoL scores, indicating more negative impact of MD on QoL, were associated with poorer distance VA (better eye r = -0.431 p < 0.001; worse eye r = -0.350 p < 0.001; binocular vision r = -0.419 p < 0.001) and near VA (better eye r = -0.326 p < 0.001; worse eye r = -0.226 p < 0.001; binocular vision r = -0.326 p < 0.001). Poorer MacDQoL scores were associated with poorer contrast sensitivity (better eye r = 0.392 p < 0.001; binocular vision r = 0.423 p < 0.001), poorer colour recognition (r = 0.417 p < 0.001) and poorer comfortable near VA (r = -0.283, p < 0.001). The MacDQoL differentiated between those with and without binocular scotoma (U = 1244 p < 0.001).ConclusionThe MacDQoL 22-item scale has excellent internal consistency reliability and a single-factor structure. The measure is acceptable to respondents and the generic QoL item, MD-specific QoL item and average weighted impact score are related to several measures of vision. The MacDQoL demonstrates that MD has considerable negative impact on many aspects of QoL, particularly independence, leisure activities, dealing with personal affairs and mobility. The measure may be valuable for use in clinical trials and routine clinical care.

Design of an individualised measure of the impact of macular disease on quality of life (the MacDQoL).

The aim of this study was to design an individualised questionnaire to measure the impact of macular disease (MD) on quality of life (QoL). Principles underlying the Schedule for the Evaluation of Individual Quality of Life (SEIQoL) interview method and the Audit of Diabetes-Dependent Quality of Life (ADDQoL) diabetes-specific questionnaire influenced the Macular Disease-Dependent Quality of Life (MacDQoL) design. The MacDQoL specifies domains of QoL that were selected using focus group methodology and refined following a postal pilot study of members of the UK Macular Disease Society (MDS). Respondents rated the impact of MD on each domain and the importance of each domain to their QoL. Mean domain scores from 69 respondents indicated that MD had a negative impact on all the domains of QoL investigated in the measure. There was preliminary evidence of good internal consistency reliability (Cronbachs α= 0.93, n = 37). Respondents who were registered partially sighted (P/S) or blind reported poorer QoL than those who were not registered (Kruskal–Wallis:χ2= 14.03, n = 62, p < 0.001). This evidence suggests that the measure will be sensitive to subgroup differences. The instrument has been further refined following the pilot study. The MacDQoL is being used in clinical trials and psychometric evaluation of the measure will be carried out using trial data. The measure is available for clinical use and has been linguistically validated in 15 other languages.

Psychometric evaluation of the 12-item Well-being Questionnaire for use with people with macular disease

This paper reports the evaluation of a generic measure of psychological well-being, the 12-item Well-being Questionnaire (W-BQ12), for use with people who have the chronic eye condition, macular disease (MD). The W-BQ12 was incorporated in a self-administered questionnaire which was completed by 1421 members of the Macular Disease Society (MD Society). Unforced factor analysis elicited the expected three factors representing constructs of positive well-being, energy and negative well-being. A forced single-factor solution supported use of the whole scale to measure total general well-being. High Cronbachs α coefficients demonstrated good internal consistency reliability in the entire scale (α = 0.87) and in subscales (α > 0.78). The factor structure matched that found in samples of people with diabetes for whom the W-BQ12 was first developed, indicating construct validity. Expected subgroup differences in the MD sample indicated significantly poorer well-being in women than in men and also in participants who were registered blind or partially sighted compared to those who were not registered. The W-BQ12 will be useful in measuring outcomes in rehabilitative and medical interventions and in researching factors affecting adjustment to MD.

The MacDQoL Individualized Measure of the Impact of Macular Degeneration on Quality of Life: Reliability and Responsiveness

PURPOSE To investigate the MacDQoL test-retest reliability and sensitivity to change in vision over a period of one year in a sample of patients with age-related macular degeneration (AMD). DESIGN A prospective, observational study. METHOD Patients with AMD from an ophthalmologists list (n = 135) completed the MacDQoL questionnaire by telephone interview and underwent a vision assessment on two occasions, one year apart. RESULTS Among participants whose vision was stable over one year (n = 87), MacDQoL scores at baseline and follow-up were highly correlated (r = 0.95; P < .0001). Twelve of the 22 scale items had intraclass correlations of >.80; only two were correlated <.7. There was no difference between baseline and follow-up scores (P = .85), indicating excellent test-retest reliability. Poorer quality of life (QoL) at follow-up, measured by the MacDQoL present QoL overview item, was associated with deterioration in both the better eye and binocular distance visual acuity [VA] (r = 0.29; P = .001, r = 0.21; P = .016, respectively; n = 135). There was a positive correlation between deterioration in the MacDQoL average weighted impact score and deterioration in both binocular near VA and reading speed (r = 0.20; P = .019, r = 0.18; P = .041, respectively; n = 135). CONCLUSION The MacDQoL has excellent test-retest reliability. Its sensitivity to change in vision status was demonstrated in correlational analyses. The measure indicates that the negative impact of AMD on QoL increases with increasing severity of visual impairment.

Effect of age related macular degeneration on the Eger macular stressometer photostress recovery time

Aim: To assess the repeatability of Eger macular stressometer (EMS) measures of photostress recovery and determine their association with other measures of visual function. Methods: EMS photostress recovery time was measured in 90 patients with bilateral exudative age related macular degeneration (AMD), 19 with bilateral atrophic AMD and 47 with both forms of the condition (mean age 79 (SD 13) years). Measurements were made on two occasions separated by 1 year. Intrasession repeatability was assessed by repeating the measures after a 10 minute recovery period at the first visit. Distance visual acuity was measured with a logMAR chart, near visual acuity with a MNRead chart at 25 cm, contrast sensitivity with a Pelli-Robson chart, and the presence of central visual disturbance assessed with an Amsler grid. A questionnaire was used to assess self reported difficulties with glare recovery. Results: The average EMS recovery time was 11.0 (SD 8.9) seconds, decreasing by 1.6 (5.2) seconds on repeated measurement (p<0.05). EMS photostress recovery was not correlated with visual function measures or subjective difficulties with lights (p>0.05). EMS photostress recovery time did not predict those whose vision decreased over the following year compared with those among whom it remained stable. Conclusions: The EMS test is not a useful tool in determining the severity or progression of AMD.

Comments on Speight et al.'s 'Not all roads lead to Rome―a review of quality of life measurement in adults with diabetes'

We welcome Speight et al.’s review of quality of life measurement in adults with diabetes [1]. The discussion of the importance of differentiating quality of life from constructs such as health status, well-being and treatment satisfaction is useful in addressing a continuing confusion in the literature. Also we are pleased to see the positive reviews of the Audit of Diabetes-Dependent Quality of Life (ADDQoL), Diabetes Treatment Satisfaction Questionnaire (DTSQ) and Well-Being Questionnaire (W-BQ12). However, we would like to comment on remarks about the ADDQoL and provide updates on all three measures. Speight et al. cited the Food and Drug Administration (FDA) 2006 draft guidelines on Patient Reported Outcome measures which advised against questions requiring judgements about hypothetical situations. While this advice is sound in some instances, there are major benefits of the design of ADDQoL items which ask respondents how aspects of their life would change if they did not have diabetes (see response to FDA draft guidance by Clare Bradley published at http://www.fda.gov/ohrms/dockets/dockets/06d0044/06d-0044-EC18-Attach-1.pdf. A direct question about the impact of diabetes often elicits optimistic coping responses suggesting little or no impact while asking ‘but what if you didn’t have diabetes?’ would elicit a more realistic response.

Measuring Quality of Life in Macular Degeneration

Patient-reported outcomes are increasingly used in research and clinical practice in ophthalmology as in other medical specialties. Measures of health status, psychological well-being, functional status, and visual function are frequently referred to as quality of life (QoL) measures and have been used as such in research into macular degeneration (MD). However, such patient-reported outcomes do not measure QoL, although the constructs may be related to or influence QoL. When inappropriate or insensitive measures are used as QoL measures, the findings can be misleading and may lead to incorrect management of patients. Care is needed in the selection of patient reported outcomes (PROs) for use in research and clinical practice to ensure that they are appropriate for the intended purpose. In addition, PROs should be psychometrically validated, demonstrating qualities including face, content and construct validity, internal consistency and testretest reliability and responsiveness. Utility values obtained using methods such as time trade-off and standard gamble are used to calculate quality adjusted life years and frequently referred to as QoL measures. However, they do not measure QoL and give no impression of the ways in which MD or any other medical condition impacts on QoL. For older people, such as those with MD, the questions are particularly difficult to answer. PROs have shown that MD has a considerable negative impact on the lives of people with the condition and on their families. The use of PROs is valuable in assessing the impact of clinical and rehabilitative interventions and other services for people with MD. Ideally a complementary combination of PROs would used for evaluation purposes to ensure considerate, individually tailored and effective management of this group of patients.