Utility values indicate the perceived quality of life of patients with specific health states, and the uncertainty of therapeutic modalities is quantified. The entirety of the degree of disability of the disease (economic, social, functional, and psychological) is reflected in the measures of utility as it is experienced and weighted by the patient.14
As such it will be influenced by social factors such as religious belief, attitudes to risk and an individual’s expectations about their future life. In summary, the time trade-off (mean 0.93) and standard gamble for blindness (mean 0.85) utility values of Singapore teenagers with myopia are relatively high. The time trade-off utility value was lower for myopic students with worse presenting visual acuity of the better eye, after controlling for race and sex (visual acuity >0.3). In multivariate analysis, both utility methods were higher for students with more “academic” schooling stream and standard gamble utility method was higher for students with higher total family income. Our study achieved a high participation rate (96.6%) and included information on several factors including total family income and presenting visual acuity.
Although myopia is a readily treatable disorder, it may significantly affect visual function and quality of life.9
There may be practical difficulties associated with the wearing and maintenance of optical corrective devices, and limitations imposed on sport and career opportunities. The extent of disability may be greater if myopia is not optimally corrected with appropriate spectacles or contact lenses. The mean time trade-off was 0.93, indicating that the students were willing on average to sacrifice 7% of expected life years for perfect health associated with emmetropia. The mean standard gamble for blindness was 0.85; the teenagers were willing to accept a 15% risk of blindness associated with a treatment that cures myopia. We did not compare the utility value for standard gamble across studies as the risk of “blindness” was evaluated in our study, rather than the risk of “death.” It has been purported that the standard gamble for death overestimates risk aversion as the idea of death evokes an emotional response. As myopia is an ocular disorder which is not associated with considerable morbidity or significant mortality, the risk of “blindness” was chosen as a more relevant complication of a hypothetical treatment for myopia. As expected, the time trade-off utility value (for blindness) for myopia (mean 0.93) was higher (denoting a better quality of life), compared with diabetic retinopathy (time trade-off utility value (for death), mean 0.77) and age related macular degeneration (time trade-off utility value (for death), mean 0.72).10,11
Attempts at comparing utility values across studies may be limited by differences in the selection of the study population and interview methods used to assess utility values.
We note that teenagers, in contrast with adults, may place different values on the impact of eye disease and life expectancy because of their youth and good health. Teenagers may be less willing to take risks in return for perfect vision than adults. As cycloplegia was not used in our study, it is possible that excessive accommodation may lead to “pseudo-myopia” in otherwise normal teenagers. Thus, both true myopes and emmetropes with pseudo-myopes may be included in our study sample and the utility values may be higher than expected. However, a validation study of cycloplegic and non-cycloplegic refraction in 670 male Singapore military conscripts (mean age 19.5 years) showed an intraclass correlation coefficient of 0.99 for refractive error.3
The time trade-off utility value for myopia decreased (mean 0.92) for teenagers with presenting logMAR visual acuity worse than 0.3, compared with teenagers whose better eye presenting logMAR visual acuity was better than 0.3 (mean = 0.94), after controlling for race and sex (p=0.005). This difference in time trade-off utility value (0.02) appears small, but may be of clinical significance. For example, if a teenager reports that he or she expects to live to 80 years and the number of years willing to sacrifice for a new technology to restore emmetropia is 6.5 years, then the reported time trade-off utility value is 0.92; while another teenager who expects to live to 80 years but will sacrifice only 5 years of life will have a time trade-off utility value of 0.94. Non-optimal or no correction of myopia with spectacles or contact lenses may impair vision and diminish quality of life of myopic teenagers. Ophthalmologists, optometrists, and the general public should be educated about the need for regular annual eye checkups for all myopic individuals.
In previous studies of other eye diseases, the utility values were lower for patients with worse best corrected visual acuity (Table 1). In the United States, the time trade-off utility values of 80 white patients with age related macular degeneration and 100 patients with diabetic retinopathy were lower concomitantly as the corresponding best corrected visual acuity in the better eye decreased.10,11
In our present study, the utility values do not vary with the degree of myopia, suggesting that poor presenting visual acuity, rather than visual disability associated with the disease itself (myopia), is the main determinant affecting quality of life and patient’s perception of the value of vision.
Higher utility values using both
the time trade-off and standard gamble for blindness methods were found in students in “better” schooling streams; whereas the standard gamble utility values were higher for students with higher total family income. Students from families with lower socioeconomic status or who were in less “academic” streams tended to associate myopia with a larger detrimental effect on perceived quality of life, and may have a greater prejudice against myopia. This cannot be explained simply by a greater willingness to forego years of life, (perhaps because of different perceptions of their future quality of life), because the standard gamble is also lower. The reporting of information such as total family income among teenagers may be inaccurate or biased. However, it is likely that this misclassification bias is non-differential and the results tend towards the null. Similarly, the time trade-off utility values for age related macular degeneration patients were lower in adults with high school education or less (mean 0.70), than in adults with greater than high school education (mean 0.74).11
In contrast, in a study of diabetic retinopathy patients, the standard gamble utility value of adults with 12 years of education or less was higher (mean 0.91), than in adults with more than 12 years of education (mean 0.82)10
; which could perhaps reflect differing attitudes and perceptions of risks in these populations.
We explored the differences in utility values associated with the same eye condition across different ethnic or religious groups. Previous studies on the utility values of patients with diabetic retinopathy, age related macular degeneration, and blindness were conducted in primarily white populations.10–12
Patients’ perceptions towards the degree of disability associated with myopia may be influenced by social or cultural beliefs of the subject. In our multiethnic Asian study, Muslim students reported lower utility values.
In summary, the mean time trade-off and standard gamble for blindness utility values of Singapore myopic teenage students were 0.93 and 0.85, respectively. The utility values were higher in students with better presenting visual acuity, students who wore appropriate optical corrective devices, students with higher total family income, more “academic” schooling streams, and those who were non-Muslims.