72 M.C.C. Lim and K.D. Frick

need).” This is 66% in Tehran using a 20/40 visual acuity cutoff,39 and 25.2% or 40.5% in Bangladesh, using 20/40 and 20/60 visual acuity cutoffs respectively.3

Even if subjects have glasses, there is evidence from other countries that not all want to wear them. In Mexico, 493 school children received free spectacles through a local program and underwent unannounced examination within 18 months.2 Only 13.4% of them were found to be wearing spectacles. The reasons they gave included appearance of the glasses or fear of being teased. A study of Tanzanian school children showed that at 3 months, only 47% were wearing the free spectacles they had been given.40 Of 580 Chinese children owning spectacles, 17.9% did not wear them at school and a common reason for nonwear was the belief that spectacles weaken the eyes.41 In African school children, barriers to spectacles use included peer pressure, parental concern about the safety of spectacles use and their costs.42 In Southern India, a population-based study found that the prevalence of current spectacles use in those with spherical equivalent +/−3.00 Diopters or worse was 34.2%, and among those who had used spectacles previously, 43.8% discontinued because they felt either the prescription was incorrect or the spectacles were uncomfortable.37 However, there might be differences in cultural attitudes between countries as a study of Australian children found unnecessary or overuse of spectacles.43,44 The proportion of myopes with correction for each region shown in Table 7.

iii. Amount paid for myopic correction

USA

In the USA, burden-of-disease studies have been carried out on myopia. It has been estimated that US$2 billion per year in 198345 and US$4.6 billion per year in 199446 were spent in the USA on correcting myopic refractive errors. The figure in 1990 for vision products (eyeglass frames, lenses and contact lenses) for all refractive errors is higher, at $US8.1 billion.47 After adjustment for inflation (U.S. Department of Labor), this equates to $13.4 billion.

A cross-sectional study in the USA showed that 110 million Americans could and do achieve normal vision with refractive correction and the estimated cost of this was US$3.8 billion48 or approximately US$4.9 billion

73 The Economics of Myopia

today. From these studies we can estimate that the cost of optical correction of myopia lies in the range of US$2–5 billion. Since data are available, we can use them to calculate the cost per myope in order to help us calculate the cost of myopia in other countries with less data. Table 4 shows the calculation for how the number of myopes in the USA is estimated to be approximately 80 million. If we use a conservative estimate of the cost of myopia correction to be $4 billion, then the annual amount spent per myope is US$4 billion divided by 80 million which is US$50. Note that this is the average amount spent annually for all myopes, whether they wear glasses or change them regularly or not. The “true” cost is higher than this as we estimate that 95% of myopes in this population buy optical correction aids.30 The estimate may also be low because some myopes may not change glasses annually.

Singapore

The cost data for a study of Singaporean school children aged 12–17 were collected using questionnaires; the resulting estimate was that they spent an average of S$222 (US$148) per year or a median of S$125 (US$83) on glasses or contact lenses from opticians.49 Unfortunately no data are available indicating how much is spent by other demographic groups on glasses, laser refractive surgery and other complications resulting from myopia as well as days lost from work. Thus we have to use the data from the single age group to derive a bottom-up estimate for the direct costs of myopia. This bottom-up approach entails estimating the costs of single elements and then extrapolating upwards to the entire population, whereas a topdown approach might look at the global cost of myopia and then working downwards to an estimate for Singapore. Often both approaches are used to determine if the estimates are in the correct magnitude.

The result is an annual figure of S$373m, or US$250m. Table 6 summarizes the estimated total annual direct cost of myopia in Singapore. Sensitivity analyses can also be carried out to calculate the upper and lower bounds of our estimate. If we use the median annual cost of S$125 instead, the annual cost is S$180m.

It can be argued that myopia correction in older adults (the average age of the LASIK patient in a Singapore tertiary hospital is 33 years of age — unpublished data) may be more costly especially with the advent of laser refractive surgery. However, this does not necessarily result in a substantial

change in the economic cost of myopia as the cost of laser surgery may be offset by future savings in spectacles and contact lenses. Contact lenses have been shown to be more costly than LASIK, which is itself more costly than eyeglasses.50 If we take an average cost of LASIK to be US$2000 for both eyes, then this is approximately the cost of 15 years of spectacles and contact lenses, based on a mean annual cost of US$148. Javitt et al. found that PRK was equivalent to wearing daily-wear soft contact lenses for 10 years.46 The average age of the LASIK patient in Singapore is 33-years, as mentioned earlier. This patient, whom we still classify as “myopic,” has spent US$3000 on LASIK, but does not have to pay for refractive correction for the next 10–15 years, until she becomes presbyopic 10 years later, when she will start spending approximately as much as a myope annually. This is because myopes who have been rendered emmetropic by LASIK will have to purchase reading glasses when they become presbyopic in their mid 40s.