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Measuring outcomes of cataract surgery using the Quality of Well-Being Scale and VF-14 Visual Function Index

Rosen, Peter N. MD; Kaplan, Robert M. PhD; David, Kristen MPH

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Journal of Cataract & Refractive Surgery: February 2005 - Volume 31 - Issue 2 - p 369-378
doi: 10.1016/j.jcrs.2004.04.043
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Ophthalmologists, like other health care providers, have become concerned about the impact of visual problems on everyday function. Although visual acuity remains the most important physiological measure in the evaluation of patients for cataract surgery, from the patient's perspective, the inability to perform routine daily activities is often the motivation for seeking care. Visual acuity may underestimate the value of surgery because it ignores postoperative functional improvement, changes in activities of daily living, and satisfaction with vision.1–3 As a consequence, the quality-of-life, economic, and social benefits of improved vision often remain implicit. Leading ophthalmologists, along with American Academy of Ophthalmology (AAO) and the Agency for Healthcare Research and Quality (AHRQ), argue that measurement of vision-related impairment must go beyond clinical measures and be interpreted in terms of vision-specific and general health status measures (health-related quality of life).2,4–11

Furthermore, patients view impairments in vision-dependent functioning, rather than clinical measures, as having the most importance and relevance.1,8 The AAO's Cataract Preferred Practice Patterns, on which the AHRQ guidelines are based, include documenting the elimination of symptoms, restoring vision that meets patients' functional needs, and improving quality of life and satisfaction with vision. General and vision-specific measures are needed to provide this broad range of insight into the proximal benefits (highly vision dependent such as reading, sewing, driving) and distal benefits (less vision dependent such as social, recreational, and vocational activities) of surgically restoring vision.

Most studies of eye disease use vision-specific measures of quality of life, such as the 14-item Visual Function Index (VF-14),12 that ask questions specific to visual problems. Disease-specific measures, however, have limited usefulness in making comparisons between different disease states. The self-administered Quality of Well-Being Scale (QWB-SA) is a multi-attribute, preference-weighted, general health status measure that can be used in any disease population for such comparisons. Furthermore, preference-based (utility-weighted) measures such as the QWB-SA are essential for cost-effectiveness analysis. Although there has been considerable interest in measuring the cost effectiveness of treatments for cataract,13 little is known about the validity, responsiveness, and reproducibility of the QWB-SA in these patients.

Studies report evidence of the QWB-SA system's general validity as well as its validity in specific disease categories.14–16 However, applying the QWB-SA to cataract problems requires specific validation. The VF-14 has been shown to have high internal consistency and to correlate with cataract patient's self-ratings of satisfaction and trouble with vision.9 It is also reported to be reproducible (reliable) and responsive.12

In this study, we report the initial findings of an evaluation of the validity and responsiveness of the QWB-SA, version 1.04, in cataract patients and extend the previous VF-14 findings for these attributes.

Patients and Methods

Patient Selection and Study Design

Between July and November 1998, patients were selected from the practices of 9 ophthalmologists in a group practice of the Southern California Kaiser-Permanente Medical Group (SCPMG). All consecutive adult patients presenting for first-eye or second-eye cataract surgery were invited to participate. Patients scheduled for cataract surgery combined with corneal, glaucoma, or retina procedures were excluded, as were those with dementia or who were unwilling or unable to complete self-report surveys. Patients who had intraocular surgery or posterior capsule opacification requiring laser capsulotomy within 4 months of cataract surgery were also excluded. The University of California, San Diego, and SCPMG institutional review boards approved the study.

Patients were told that before surgery and approximately 1 month and 4 months after surgery, they would be asked to fill out a series of questionnaires concerning their general and vision-specific health status. They were also informed that clinical findings such as visual acuity and complications during and after surgery would be analyzed in relation to their self-reported health status. Demographic and past ocular and systemic medical data were also collected.

Enrolled patients had cataract extraction under local anesthesia by a similar small-incision phacoemulsification technique. All patients had implantation of a posterior chamber intraocular lens and placement of 1 or no sutures. Surgeries were performed on an outpatient basis.

Health Status Measures

Self-administered scannable forms were distributed to patients preoperatively and postoperatively to collect data on their overall and vision-specific functional status and to assess their perceived satisfaction or trouble with vision. The measures used were the QWB-SA (version 1.04), the VF-14, a cataract symptom scale, and global questions on satisfaction and trouble with vision.

Quality of Well-Being Scale 1.04.

Overall functioning was evaluated with the QWB-SA 1.04, a measure of preference-based general health status that assesses several components of health-related quality of life.17,18 First, it obtains observable levels of functioning using 3 scales: mobility, physical activity, and social activity. Second, from a list of 58 items, patients identify symptoms or problems that may have affected them in the past 3 days. Then, the observed level of function and subjective symptomatic complaint are weighted by preference, or the utility for the state, on a scale ranging from 0 (dead) to 1.0 (optimum function). The weights, which do not vary as a function of demographic variables including race, income, and sex,19 were obtained from independent samples of judges who rated the desirability of observable health states. Most evidence indicates that the weights do not vary systematically as a function of previous experience with the rated health state.19 This system can be used to place the general health status of any individual on the continuum between death and optimal functioning for any specified time. Thus, the score for the QWB-SA results in a summary score, which is a single number that ranges from 0 (death) to 100 (optimal health). The QWB-SA has a reliability exceeding 0.90 for most populations20 and can be completed in approximately the same time as other popular measures such as the SF-36.18

The VF-14 Visual Function Index.

Functional impairment related to vision was evaluated with the VF-14, an index of measures that estimate the difficulty patients have performing 14 vision-dependent activities of daily living such as daytime and nighttime driving, reading traffic signs or small print, and engaging in recreational activities.21 Although the VF-14 is highly correlated with self-ratings of the amount of trouble and satisfaction patients have with their vision and is somewhat correlated with overall functioning (Sickness Impact Profile), it is not correlated with measures of visual acuity.9 Scores on the VF-14 range from 0 (unable to do all activities) to 100 (able to do all activities without difficulty).

Cataract Symptom Score.

Patients were asked whether they were bothered by any of 5 symptoms (double or distorted vision; glare, halos, or seeing a ring around lights; blurry vision; colors looking different in a way that is disturbing; and worsening of vision in the past month) and if so, how bothersome the symptoms were. For each symptom, patients assigned a score of 3 if they were very bothered by the symptom, 2 if they were somewhat bothered, or 1 if they were a little bothered. A score of 0 was assigned if the patient did not have the symptom or was not bothered by it at all. The scores of the symptoms were summed, resulting in a cataract score for each patient ranging from 0 (no symptoms or not bothered by any of the symptoms) to 15 (very bothered by all 5 symptoms).

Global Measures of Vision.

The patient's overall level of satisfaction and trouble with vision was assessed with 2 questions, 1 related to satisfaction with vision and the other to trouble with vision. Responses were given using a 5-point scale. Patient self-reported estimates of trouble and satisfaction with vision have been previously correlated with the VF-149 and have been used to measure the responsiveness of the VF-14 to clinically important changes before and after cataract surgery.12

Clinical Data

Clinical data included Snellen best corrected visual acuity in both eyes, which was measured by an ophthalmologist or optometrist 10 days or fewer before surgery and 1 and 4 months after surgery. Intraoperative and postoperative complications, preexisting ocular and systemic comorbidities, and medications were also recorded. Chief complaints (functional impairments related to vision) were reported to the ophthalmologist as the reason(s) for seeking care.

Statistical Analysis

The first phase of the analysis produced descriptive statistics for all variables at baseline and at each follow-up point. These descriptive statistics included means, relative frequencies, and standard deviations. Tables summarized each variable independently at different measurement points, which were specified in the protocol, to give cross-sectional and change-over-time data. Bivariate analysis of the effect of cataract surgery on visual acuity, visual functioning (VF-14 scale), symptoms (Vision Symptom Scale), trouble and satisfaction with vision, satisfaction with surgical results, and general health-related quality of life (Quality of Well-Being Scale) was done using Pearson correlations (r) and independent and paired t tests. One-way analysis of variance was used to test the ability of the QWB-SA and the VF-14 to discriminate between categories of satisfaction and trouble with vision. Independent variables included the change in Snellen visual acuity, VF-14, QWB-SA, VF-14, and QWB scores; visual symptoms; patient satisfaction; and trouble with vision. Data were collected within 1 week before surgery and 1 and 4 months postoperatively.

Results

Patient and Ocular Characteristics

Table 1 shows the demographic characteristics of the patients. Baseline (preoperative) and 4-month postoperative data were available for 233 patients of the 321 patients enrolled in the study. The mean age of the patients was 72.5 years ± 8.6 (SD) (range 44 to 90 years); 60.5% were men. Ethnicity was not representative of the population in Southern California. Approximately 60% of patients had some college or graduate school. Half the surgeries (50.2%) were in the right eye; 67.4% of the patients had cataract surgery for the first time. Nuclear sclerosis was the dominant type of cataract. Approximately 50% of patients had ocular morbidities, and 82% had 1 or more chronic illnesses (Table 2).

Table 1
Table 1:
Patients' demographics.
Table 2
Table 2:
Baseline ocular characteristics.

Differences from Baseline to 4 Months

Visual Acuity.

Preoperatively, the median Snellen visual acuity was 20/80 in the operated eye and 20/30 in the unoperated eye; postoperatively, the median acuity in the operated eye was 20/25 (Table 3A). Before surgery, 91.8% of patients had an acuity of 20/50 or worse and 8.2% had 20/40 or better in the operated eye, 67.8% had a visual acuity of 20/50 or worse in the operated eye and 20/40 or better in the fellow eye, and 24.0% had a visual acuity of 20/50 or worse in both eyes (Table 3B). After surgery, the mean improvement was 4.5 lines of Snellen acuity and 95.7% of patients had 20/40 or better visual acuity in the operated eye. (Approximately 40% had 20/20; 30%, 20/25; 20%, 20/30; and 6% 20/40.)

Table 3A
Table 3A:
Median visual acuity at baseline and 4 months after cataract surgery (N = 233).
Table 3B
Table 3B:
Visual acuity at baseline and 4 months after cataract surgery by level of acuity.

Functional Status Score and Visual Acuity.

Visual acuity in the operated eye improved by at least 1 Snellen line in 97.5% of patients; 2.5% had no improvement (Table 4). Of those with no improvement, 1.7% (4 patients) had no change and 0.8% (2 patients) lost lines of acuity.

Table 4
Table 4:
Improvement in functional status scores and visual acuity from baseline to 4 months postoperatively.

Postoperatively, the frequency of improvement in general health-related outcomes was lower than the improvement in vision-specific outcomes (Table 4). The VF-14 and QWB-SA scores improved in 82.8% and 56.3% of patients, respectively. The satisfaction with vision and trouble with vision scores improved in 87.5% and 81.2% of patients, respectively. Although minimal improvement in clinical and functional measures occurred in some patients, it is not known whether all improvement was clinically meaningful.

Change in QWB-SA and VF-14 Scores.

The vision-specific VF-14 was more sensitive to improvements after surgery than the general health-related quality-of-life QWB-SA (Figures 1 and 2). Both measures demonstrated a greater magnitude of change with lower baseline scores.

Figure 1.
Figure 1.:
Left: Mean improvement in QWB-SA 1.04 scores and 95% confidence intervals (P<.01). Right: Mean improvement in VF-14 scores and 95% confidence intervals (P<.01).
Figure 2.
Figure 2.:
Top: Mean improvement in QWB-SA 1.04 scores in second-eye surgery cases (P<.026). Bottom: Mean improvement in VF-14 scores in second-eye surgery cases (P<.0001).

There were significant changes in the QWB-SA and VF-14 scores between baseline and 4 months in all cases except in QWB scores in 3 groups (Table 5). The first group was patients with a preoperative visual acuity of 20/40 or better in the operated eye; it is not clear whether this is a reflection of the small sample size, the large standard deviation of the difference between the means, or a “ceiling effect” due to the relatively good vision in both eyes in this group. The other 2 groups were patients with a preoperative acuity of 20/50 or worse in the unoperated eye and those having first-eye cataract surgery. This may be due to the lack of QWB-SA sensitivity to change when vision in the unoperated eye is poor.

Table 5
Table 5:
Change in QWB-SA and VF-14 scores from baseline to 4 months postoperatively.

The change in scores in patients with poor acuity (20/50 or worse) in the operated eye and good acuity (20/40 or better) in the unoperated eye was significant, demonstrating greater sensitivity of the QWB when change resulted in good visual acuity in both eyes. The significant change in QWB scores in patients having second-eye surgery confirms these findings and the added benefit of second-eye surgery (Figure 2, top).

There were significant changes in VF-14 scores in patients with good or poor preoperative visual acuity in either eye. The VF-14 was most sensitive in patients with an acuity of 20/50 or worse in the unoperated eye. However, the results were highly significant when acuity was good in the operated eye and in patients having first-eye cataract surgery, demonstrating that vision-specific measures capture clinically important change even when improvement occurs in 1 eye only. The benefit of second-eye surgery was also demonstrated by the VF-14 (Figure 2, bottom).

Correlation Between Variables After Cataract Surgery

The QWB-SA and VF-14 were significantly correlated with satisfaction and trouble with vision, self-rating of vision, visual symptoms, and visual acuity in the operated eye (Table 6A and Figure 3). Satisfaction with the surgical results was also correlated with the QWB-SA and VF-14 but not with visual acuity in the operated eye (Table 6B and Figure 3).

Table 6A
Table 6A:
Postoperative correlations between QWB-SA and VF-14.
Figure 3.
Figure 3.:
Correlation between variables after cataract surgery (P<.01) (GHP = general health perception; QWB = Quality of Well-Being Scale, VF-14 = Visual Function Index; VHP = visual health perception).
Table 6B
Table 6B:
Postoperative correlations between patient satisfaction and surgical results.

Discussion

Our finding of improved visual acuity in the operated eye is similar to the finding reported by Steinberg et al.9 Improvement by 2.0, 3.0, or 4.5 lines of Snellen acuity occurred in 92.7%, 85.4%, and 68.1% of patients, respectively. Beyond improvements in acuity, our study offers evidence of the validity and responsiveness of the self-administered QWB-SA in patients having cataract surgery. Previous studies used vision-specific and general health-related quality-of-life measures to assess the benefits of cataract surgery.6,8,9,21–24 General measures are less sensitive to change and, therefore, are thought to be less useful for individual clinical decision making. However, vision-specific measures cannot be used to compare vision-related conditions and conditions not related to vision or to evaluate the benefits of surgery in terms of the overall health-related quality of life. Increasingly, these kinds of evaluations are needed to resolve policy issues related to benefits coverage, resource allocation, and quality of care in different practice settings.13,25,26 Our results are also consistent with previous reports that showed a significant correlation between patient satisfaction with vision and health-related quality of life but not between visual acuity and functional measures.9 These findings suggest that visual acuity is not a good predictor of patient satisfaction or functioning after cataract surgery.27

Previous findings of the responsiveness of the VF-14 were replicated in this study and support the concept of its use in clinical trials and clinical care. Like Steinberg et al.9 and Cassard et al.,12 we found the VF-14 was responsive to several validated indicators of clinical changes (ophthalmologist measurement of visual acuity; patient-reported satisfaction and trouble with vision). The QWB-SA was responsive to the same indicators of clinical change, although to a lesser degree than the VF-14.

Our study also considered which patients benefit most from cataract surgery. The QWB-SA and VF-14 were most responsive in cases with greater preoperative impairment and greater postoperative improvement when impairment was stratified by trouble or satisfaction with vision rather than by visual acuity. At small and moderate levels of visual acuity impairment (20/30 to 20/70), responsiveness was similar for each level of satisfaction and trouble with vision. Responsiveness increased as impairment increased beyond 20/80, indicating that low and moderate visual acuity impairment is a poor predictor of functional improvement after cataract surgery and that a greater decline in visual acuity is a better predictor.

About one third of the study population had previous cataract surgery, 84% of which had 20/30 or better visual acuity at the time of second-eye surgery. In this group, improvements between baseline and 4 months were significant for the QWB and VF-14. These results confirmed the significant benefit of second-eye surgery found by others2,28–30 and extend this work by demonstrating improvement in general health status and vision-specific activities.

Preoperatively, only visual acuity in the unoperated eye was significantly correlated with the QWB-SA and VF-14, while visual acuity in the operated eye was not. Postoperatively, however, visual acuity was only correlated with the QWB-SA or VF-14 scores in the operated eye. These findings suggest that visual acuity underestimates limitations of functioning before surgery and improvements after surgery in first-eye and second-eye surgery.

Limitations of this study include the use of a nonrandomized sample, traditional Snellen rather than logMAR visual acuity, and small sample sizes. Furthermore, all patient-reported measures in this study use ordinal scales. Dividing continuous scales into categories may cause difficulties in scaling, scoring, and analysis.31 It is not clear, for example, whether increments between categories are equal, too broad or coarse, or truly represent the range of clinically useful information. Last, there was no control group (ie, patients who did not have surgery). We hesitate to draw conclusions about the effect of surgery in the absence of a true randomized trial. However, a recent study32 reports that patients who elected to have cataract surgery had significant improvements in functional outcomes while those who declined surgery stayed the same or became worse. Future studies should evaluate the effects of new approaches to the management of cataract using standardized health outcome measures, continuous scales when possible, and randomized clinical trial designs.

In conclusion, the QWB-SA and the VF-14 are reproducible, responsive, and discriminating measures of health-related quality of life in patients having cataract surgery and can be used for clinical trials, technology assessment, and policy analysis. Unlike the VF-14, the QWB-SA can be used across different diseases and conditions and for cost-effectiveness and cost-utility analyses. Furthermore, using clinical measures—vision related and general health status—together may allow direct mapping of proximal to distal improvements in health outcomes. It would be important to directly link, for example, improvements in vision to the impact on other comorbidities, utilization of health services, safety, mobility, and independent living.

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