Introduction

84 E.L. Lamoureux and H.-B. Wong

essential to determine the effectiveness of controlled clinical trials, clinical audit, or outcomes research.

Since the measurement of patient-reported health outcomes aims at understanding the effect of ocular diseases or impairment taken from the patient’s perspective, there has been a plethora of instruments developed to measure these concepts. Confusingly however, many authors refer to instruments that simply measure disability or functioning as quality of life (QoL). Disability is the limitation of a person’s ability to perform activities caused by a medical condition. Visual disability or restricted visual functioning would be more appropriately called vision-related activity limitation as advocated by the World Health Organization (WHO) International Classification of Functioning, Disability and Health (ICF).4 Compared to disability and functioning, health-related quality of life (HRQoL) is a broader concept, which encompasses many issues that impact a person’s life. HRQoL usually refers to the effect of a disease on the way a person enjoys life, including the way the illness affects a person’s ability to live free of pain, to work productively, and to interact with loved ones. These issues are usually grouped into domains such as well-being, symptoms, work/economic concerns, cognition, independence, and social interaction.

There have been two common methods of assessing HRQoL. The first involves generic instruments that measure broad aspects of health. Generic HRQoL instruments provide a general sense of the effects of an illness but not a particular medical condition. The Medical Outcomes Study ShortForm Health Survey (SF-36) is one most used generic HRQoL instruments.5 The major limitation of generic HRQoL instruments is that they do not assess potential condition-specific domains of HRQoL. Because of this, they may not be sensitive enough to detect subtle treatment effects. The second approach to measure HRQoL involves the use of instruments that are specific to a disease. Measures geared toward specific diseases or populations are likely to be more sensitive, and therefore, to have greater relevance to practicing clinicians. Vision-specific HRQoL therefore investigates the impact of vision impairment on QoL, examining both the impact and importance of each domain on QoL and allowing for variability in the relevance of specific domains to individual respondents.

The measurement of the impact of myopia from a patient’s point of view has been advocated in recent years. In this chapter, we provide a critical assessment of the research associated with the impact of myopia on generic HRQoL, vision-specific functioning, and vision-specific HRQoL.

85 Quality of Life and Myopia

Impact of Myopia in Children, Adolescents and

Young Adults

In spite of the high prevalence rates of myopia in children, adolescents, and young adults, particularly in Asian countries, there is a paucity of research that has investigated myopia’s impact on functioning or HRQoL in these younger populations (Table 1). The Pediatric Quality of Life Inventory Version 4.0A (PedsQL 4.0) was recently utilized to assess the impact of myopia in 1249 Singaporean adolescents aged 11 to 18 years.6 The 23-item PedsQL 4.0 measures the core physical, mental, and social health dimensions as delineated by the World Health Organization, as well as role (school) functioning.7 The scale comprises parallel child self-report and parent-proxy report formats for age ranges of 5 to 7, 8 to 12, and 13 to 18 years. Respondents are asked about the difficulty of performing each item over the past month (e.g. “It is hard for me to run”).8 Responses are made on a five-point Likert scale and scores are transformed to a 0 to 100 scale. Total and two subscale scores, i.e. physical and psychosocial health summary scores, can then be derived, with higher scores indicating better HRQoL. The total scores reported by high and low myopic adolescents were not significantly different when compared to adolescents without myopia (p > 0.05). This study, however, showed that presenting visual impairment (VA [visual acuity] < 6/12) was associated with diminished total HRQoL, psychosocial, and school functioning scores in healthy

Table 1. Details of Studies that have Investigated the Impact of Myopia on Generic Health and Vision-specific Functioning in Children, Adolescents, and Young Adults

86 E.L. Lamoureux and H.-B. Wong

adolescents without any medical problems. Since the best-corrected VA was not assessed, visual impairment attributable to uncorrected refractive error could not be determined in these adolescents.

Other generic HRQoL methods have also been used to determine the impact of myopia. Utility values are measures that assess the QoL associated with a health state.9–11 Utility values traditionally range from 1.0, associated with perfect health, to 0.0, associated with death. Scores approximating a value of 1.0 indicate a better QoL associated with a health state. Conversely, those closer to 0.0 suggest poorer levels of QoL.9 Time-Trade-Off (TTO) is also another technique used to help determine the QoL of a patient or group. Similarly, the Standard Gamble (SG) technique is a traditional technique of measuring preferences under uncertainty. It is used to measure utility functions over life-years and health states, as well as the preference weights to be used in the Quality Adjusted Life Years (QALY) calculations.12 Two studies in Singapore have been conducted to examine the utility values in myopic students. The first involved 699 myopic students aged 15 to 18 years who reported that the mean time trade-off (years of life willing to be sacrificed) and standard gamble (risk of blindness from therapy willing to be sacrificed), utility values for treatment of myopia were not related to the severity of myopia.13 They reported that myopic teenagers with better presenting visual acuity (LogMAR [Logarithm of the Minimum Angle of Resolution] <0.3), for those who wore glasses or contact lenses, had a higher total family income, had more “academic”schooling, and were non-Muslim, reported higher utility values.

Another Singaporean study of 120 university myopic medical students aged 18 to 22 years examined time trade-off and standard gamble utility values for treatment of myopia. No relationship between utility values and severity of myopia was found. The utility values reported was higher (time trade-off 0.97 and standard gamble for death 0.99)14 than those obtained from other ophthalmic conditions, such as diabetic retinopathy and age-related macular degeneration, suggesting myopia may have less impact compared to other ocular conditions. Also, as the medical students included in this study differed in age, education level, religion, and race from the general adult population in Singapore, these results may not be generalizable to the population.

Data on the impact of myopia on vision-specific functioning (VSF) is also very scarce. A visual functioning questionnaire was used to assess the impact of myopia in rural Chinese secondary school children.15 In this cohort of middle school children, myopia was significantly and