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limited available evidence, more work is needed to gain a better understanding of the impact of myopia on vision-specific functioning and HRQoL in children and younger adults not only in Asia but also other countries. In adults, unilateral visual impairment associated with refractive error (including myopia) appears to have a limited impact general health. However, bilateral correctable visual impairment and severe stage myopia negatively impact general and vision-specific HRQoL. Correction of myopia does not impact on vision-specific functioning24 although more information is needed to establish its impact on emotional well-being and social inclusion.25
Future Studies
Future work to improve the understanding of the impact of myopia should focus on myopia-specific QoL scales, which include a number of life domains such as well-being, economic concerns, cognition, independence, and social interaction. Our understanding of the impact of myopia in these areas is limited. There is also a need for future investigators to use modern psychometric methods to analyze questionnaire data. With the exception of one study, most studies have used Classical Test Theory methods such as a mean or summary score.24 Summary scoring, termed Likert scoring, allocates an ordinal assignment of a numerical value to a participant’s response and assumes a score based on an interval scale. The validity of such summary scores has been questioned by the Item Response Theory (IRT) methods, namely Rasch analysis.2,33–36 Rasch analysis states that the probability of an individual choosing a response on a particular item depends on both the person’s ability and item difficulty. Thus, Rasch analysis is taken as a criterion for the structure of the responses, which should be satisfied rather than a simple statistical description of the responses commonly evidenced in studies that have investigated the impact of myopia. Once the data fits the Rasch model, estimates of measures on an interval scaling are provided, which can improve the accuracy of scoring and remove measurement noise.35,37–39 The transformed score can then be used in analysis of variance and regression more readily than the raw score, which has floor and ceiling effects. The utilization of some form of IRT in future studies will ensure an improved measurement of the impact of myopia on HRQoL.
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Finally, reports have suggested that there is an “epidemic” of myopia in Asia. Population-based studies in urban Asian cities indicate a high prevalence of myopia compared to European-derived populations.40–42 Paradoxically, there has been very little work undertaken in these countries to better understand the impact of myopia, particularly in adults. Valid vision-specific QoL questionnaires are needed to determine the impact of myopia and refractive error on all aspects of daily living in Asian countries. Several scales have been developed in Western countries, such as the Refractive Status and Vision Profile,17 the National Eye Institute Refractive Quality of Life,43 and the Quality of Life Impact of Refractive Correction.39 These scales either should be validated in Asian cultures or new scales specific to Asian countries need to be developed and validated, preferably using IRT methods.
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