Editorials

Correcting refractive error in low income countries

BMJ 2011; 343 doi: http://dx.doi.org/10.1136/bmj.d4793 (Published 09 August 2011) Cite this as: BMJ 2011;343:d4793
  1. Lisa Keay, senior research fellow1,
  2. David S Friedman, professor of ophthalmology and international health2
  1. 1Dana Center for Preventive Ophthalmology, Wilmer Eye Institute and Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD, USA
  2. 2George Institute for Global Health, University of Sydney, Sydney, NSW 2000, Australia
  1. david.friedman{at}jhu.edu

Self refraction has limitations, but is a viable approach to measuring refractive error

Refractive error affects millions of people worldwide. Although spectacles are an effective way of correcting refractive error, about 153 million people globally are visually impaired (vision <6/18) simply because they do not have spectacles to correct their vision.1 Myopia, the most common form of refractive error, has a prevalence of about 10-30% in most Western countries, but this figure is as high as 80% in parts of Asia.2 Poor vision in children as a result of uncorrected refractive errors is a pressing public health concern in countries like China, where about six million children have such errors.1

This problem could be eliminated with proper service delivery. “Spectacle coverage” is a valuable metric that takes into account the prevalence of refractive error and the proportion of those affected who have spectacles to correct their vision. In the linked study in rural China by Zhang and colleagues (doi:10.1136/bmj.d4767),3 spectacle coverage was estimated at 45% for children aged 5-15 years, far lower than that in urban parts of China (85%).1 Furthermore, myopic refractive error is likely to progress during school years, and maintaining appropriate spectacle correction requires regular services for children in these age groups.

In high income countries, the cost of spectacles varies widely. In the United States, the median price for a pair of spectacles (including the cost of refraction) is more than $200 (£122; €138), and annually billions of dollars are spent on refractive correction.4 Such spectacles are typically custom made, with lenses cut to fit a frame of choice. Off the shelf spectacles or “ready-made spectacles” are being used in several low income countries to provide a low cost alternative to custom made ones.5 6 7

Ready-made spectacles can cost as little as $0.50 a pair,8 and the acceptance of these spectacles is high.9 Zhang and colleagues evaluated a new approach to refraction that could simplify the entire process and reduce costs. Using a cross sectional design, the authors compared corrected vision in adolescents aged between 12 and 18 who had all of the following: self refraction without cycloplegia (paralysis of near focusing ability accomplished with topical eye drops), automated refraction without cycloplegia, and subjective refraction by an ophthalmologist with cycloplegia. The authors found that vision corrected with the self refraction was within one line of 6/6 visual acuity in 97% of students, indicating that excellent acuity can be attained in most students with this technique.

Self refraction, as described in the paper, can measure only spherical refractive error, so some people with astigmatism will not be fully served by this approach. However, this measurement is appropriate for using an inventory of ready-made spectacles, which are spherical lenses that correct only long or short sightedness and do not correct for astigmatism. These low cost spectacles could be provided easily and efficiently to underserved regions. The process of self refraction described by Zhang and colleagues, which was supervised by a teacher trained in the technique, was highly successful in rural China, where most students with refractive error have myopia. Studies performed in other populations need to confirm this finding, and if they do, a new standard could be set for using them in low income countries. Adjustable spectacles have fluid filled lenses and increasing the volume within the fluid filled lenses can change the power of these lenses. As the authors note, adjustable spectacles are currently too expensive to be used as both the method of refraction and to correct the refractive error identified because they cost nearly $20, which is more than many annual per capita health budgets in developing countries. In addition, the cosmetic acceptability and durability of these spectacles remains to be explored. The immediate application of self refraction is therefore to measure spherical refractive error (which ignores astigmatism). Spectacles can then be supplied from a supply of ready-made spectacles.

The most important results presented by Zhang and colleagues are the comparisons of self refraction with gold standard refraction.3 The authors report that the median difference was zero and 97% of participants were within one diopter of the gold standard refraction. It is reassuring that the new refraction technique does not systematically overcorrect myopia in schoolchildren (as might be expected given the tendency of children to accommodate when being refracted without cycloplegia). Because of the high prevalence of myopia in the Asian region, there is concern about increasing reliance on spectacles. Although the association between using spectacles and increasing myopia has not been proved, spectacle programmes should be mindful of not prescribing glasses that are stronger than needed. Zhang and colleagues’ results suggest that self refraction does not lead to overcorrection, a problem associated with autorefractors.

The World Health Organization’s 2009-13 action plan for the prevention of avoidable blindness calls for development of “sustainable, affordable, equitable, and comprehensive eye care services.”10 Although self refraction is aligned with the goal of providing adequate primary eye care, the implementation of self refraction programmes will need to be mindful of the limitations. The most pressing concern is that ophthalmic eye disease (which was present in about 4% of the children in Zhang and colleagues’ study) could be missed. However, in the age range studied, little could have been done to improve the vision of those with pre-existing conditions. Programmes should endeavour to incorporate a process for examining those with poor vision even after self refraction.

Although less sinister, uncorrected astigmatism or hyperopia in children can cause eye strain, blurred vision, or avoidance of reading and other tasks with close viewing distances. Screening based on visual acuity does not reliably detect hyperopia or astigmatism.11 A “fogging” test can be used to screen for hyperopia. This test involves looking to see if vision is blurred, as would be expected, with plus powered (convex) lenses; people with hyperopia would see clearly through plus lenses.12

Even with these limitations, because of the shortage of personal eye care, the number of children and adults who could see well if only they had a pair of glasses argues for consideration of simplified service delivery models. The evaluation presented by Zhang and colleagues shows promise for the use of self refraction as part of refractive service delivery.

Notes

Cite this as: BMJ 2011;343:d4793

Footnotes

  • Research, doi:10.1136/bmj.d4767
  • Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Provenance and peer review: Commissioned; not externally peer reviewed.

References