71 The Economics of Myopia

ii. Proportion of myopes paying for correction

Uncorrected and undercorrected refractive error, spectacle coverage rate and reasons for spectacles nonwear

Because myopes who do not wear glasses are not included in our calculation, an estimate of the percentage of myopes who do not wear or no longer wearing glasses is needed to complete the calculations. Studies show that there is a large range of uncorrected or undercorrected refractive error in various populations (Table 5). Uncorrected refractive error refers to individuals with refractive errors who do not use any form of refractive correction, while undercorrected refractive error includes individuals with uncorrected refractive errors and individuals with refractive errors that are undercorrected by their prescriptions. Undercorrected refractive error is also usually defined as improvement of at least 2 lines of visual acuity in the better eye with the best possible refractive correction.

From these studies we can estimate the number of myopes who are paying, or not paying for vision correction. It has been estimated that there are 153 million people aged 5-years and above worldwide with uncorrected refractive error.38

Uncorrected refractive error can also be measured using a spectacle coverage rate. This is the proportion of people with refractive error who have glasses and can be expressed as the fraction “met need/(met need + unmet

Table 5. Uncorrected or Undercorrected Visual Acuity Globally