Two quality of life assessments for AMD patients differ, study finds

More than half of patients were unwilling to ‘trade’ any of their expected remaining years of life for improved vision, authors say.

ByErin L. Boyle

In attempting to assess the relative priorities in quality of life in patents with age-related macular degeneration, researchers found that two methodologies told two stories.

The group of investigators, led by Prof. Peter A. Aspinall, employed two methods of assessment on a group of 122 AMD patients, classified according to macular morphology. They published their results in the online version of the British Journal of Ophthalmology.

The researchers found that the two methodologies, a time trade-off (TTO) method and conjoint analysis (CA), did not correlate in assessing the quality of life or priorities of these patients. Therefore, while each methodology has its own merits, those attempting to gauge these variables should use caution when interpreting data obtained via TTO or CA.

“The [United Kingdom] National Institute for Clinical Excellence has suggested that studies about the value or utility of health care interventions should use only three different methodologies, either standard gamble, TTO or discrete choice methods,” the study authors said.

They chose to compare the latter two methods, opting not to consider the standard gamble approach, because they felt that most people “do not use probabilities rationally,” the authors said.

The mean age of the patients was 77.8 years. Researchers categorized patients’ AMD severity into four grades for monocular and three categories for binocular. Visual function was measured, and patients took a functional quality of life questionnaire, the NEI VFQ-25, to be used as a standard of comparison against the TTO and CA methods.

In tests of visual function, patients’ mean logMAR distance visual acuity was 0.49, and mean logMAR near visual acuity was 0.72. Mean Pelli-Robson contrast sensitivity was 1.10.

Two methodologies

The TTO method involved asking patients to assume they had 10, 20 or 30 years to live and to state how many of these years of life expectancy they would “trade” for improved or perfect vision.

Responses to the TTO question showed that patients were no more willing to “trade” years, or months, in exchange for better vision, Prof. Aspinall and colleagues said.

CA involved comparing the utilities derived for five life-quality attributes: difficulty reading or seeing fine detail; difficulty pouring liquids and performing household chores; difficulty with glare from bright lights; difficulty with outdoor mobility; and difficulty recognizing faces.

Utilities were measured on a scale of 0 (equivalent to death) to 1 (perfect health), the authors noted. They also rated AMD severity (mild, moderate, severe and wet vs. dry) and visual function.

The researchers administered a questionnaire in which the patients were asked to rate how profiles of two fictional people coped with daily life based on the five attributes. The question was: “If you were in the shoes of one of these people, which person, in your opinion, is the worse off?”

Answers from patients

Slightly more than half of the patients were unwilling to “trade” any expected remaining years for a hypothetical cure for their AMD- related visual impairment, the authors noted.

The mean ages of patients expecting to live another 10, 20 and 30 years were 81.5, 76.8 and 68.5 years, respectively.

The three life expectancy groups showed no significant difference in binocular best corrected visual acuity, near visual acuity or binocular AMD severity. However, the group expecting to live the longest had significantly better contrast sensitivity than the other two groups, the authors said.

“For these people, the status quo is preferred to the gamble of gaining an improved state of vision,” the authors said. The oldest patients in the group were more willing than the youngest patients to trade more of their remaining years for perfect vision. The mean age of patients trading less than 50% of their expected remaining years was 76.7 years. The mean age of those trading more than 50% of their remaining years was 80.4 years.

The researchers determined there was no significant effect of AMD type on respondents’ expected remaining years or on the percentage of years that patients would trade for perfect vision.

The mean utility of all patients, including those unprepared to trade, was 0.805. The mean utility of those willing to trade their expected remaining years for improved vision was 0.575. Utility was significantly reduced as visual acuity decreased from logMAR 0.0 to logMAR 1.30 (P < .001), the authors said.

An analysis of individual utilities showed two “relatively independent” patient clusters: one with outdoor mobility as its highest preference and one with reading as its top priority.

Patients considered moving around outside to be twice as important as recognizing faces.

Statistical analysis showed that utilities derived by CA were not influenced by a patient’s level of visual impairment or AMD severity, the authors said.

“Results show that the two methods for assessing utility are poorly related,” the authors said. “TTO relates moderately to visual function and disease severity but CA does not. … Further work is needed and caution required interpreting data obtained using these methodologies for determining relative importance in vision-related quality-of-life studies.”

For more information:

Prof. Peter A. Aspinall can be reached at Heriot-Watt University, Riccarton, Edinburgh EH14 3AZ, Scotland; +131-451-8160; fax: +131-451-3161; e-mail: p.a.aspinall@sbe.hw.ac.uk.

This work was supported by an unrestricted research grant from Allergan Europe to the Visual Impairment Research Group, Heriot-Watt University, Edinburgh, UK.

Reference:

Aspinall P, Hill A, et al. Quality of life and relative importance: A comparison of time trade-off and conjoint analysis methods in patients with age-related macular degeneration. Br J Ophthalmol. Jan. 17, 2007; [Epub ahead of print].

Matt Hasson is an OSN Staff Writer who covers all aspects of ophthalmology. He focuses on regulatory, legislative and practice management topics.