For over one billion people in the developing world, glasses are a distant dream. Access to eyecare is almost non-existent in sub-Saharan Africa, and highly restricted in other parts of the developing world. It is beyond the reach of hundreds of millions of the world's growing urban poor.
A lack of proper eyesight has direct effects for those affected by it; a reduction in productivity at work, a closing-off of new opportunities, a reduction in quality of life, a possible deterioration in general health and possibly preventable blindness.
The scale of the problem is massive - the World Health Organization has pinpointed refractive error (the technical term for improperly corrected vision) as the number one cause of low vision in the world today, and the second greatest cause of preventable blindness after cataracts. Estimates place the number of people who need vision correction (or will need it in the future) and lack it at well over one billion.
The problem is set to get worse, as epidemiological studies have determined that refractive error is on the rise as the populations of developing nations become more urban. Increasing life expectancy will also cause an increase in the number of people who will suffer from presbyopia - the inability to focus on close objects, requiring reading glasses.
Using the World Health Organization's recommended measure of a health issue's effect (the Disability Adjusted Life Year), refractive error will rise into the top ten global health issues affecting productivity and opportunities by 2030, passing HIV/AIDS in its global burden.
The greatest barrier to effective treatment is a lack of trained optometrists. Many developing nations have as few as one optometrist for every million of the population. (For comparison, the figure in the UK is around 1 per 8,000.) A lack of dedicated facilities and equipment also limits access to eyecare. Compounding this issue, the cost of traditional eyewear is prohibitive for the many people surviving on less than one dollar per day.
J. D. Silver, The Optician (2013)
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M. He, N. Congdon, G.E. MacKenzie, Y. Zeng, J.D. Silver, L. Ellwein, Ophthalmology, Vol 118 (2011)
M. G. Douali and J. D. Silver, Ophthalmic and Physiological Optics, Vol 24 (2004)
J.D. Silver, M.G. Douali, A.S. Carlson and L. Jenkin, South African Optometrist, Vol 63 (2003)
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J.D. Silver, D.N. Crosby, G.E. MacKenzie, M.D. Plimmer
D.N. Crosby, M.G. Douali, G.E. Mackenzie, M.D. Plimmer, R. Taylor, J.D. Silver
J.D. Silver, D.N. Crosby, M.G. Douali, G.E. Mackenzie, M.D. Plimmer
G.E. Mackenzie, J.D. Silver, D.N. Crosby, M.J.A. Newbery, A.K. Robertson
This page contains information on various adjustable (or adaptive) lens technologies that are suitable for application to spectacles for the developing world.
Our eyes incorporate a flexible lens (the crystalline lens) - it allows us to change our focus to far or near objects (accommodation). The lens is surrounded by a ring muscle (the ciliary muscle), which relaxes to allow the lens to flatten or contracts to cause the lens to bulge, changing its refractive power.
Unfortunately, there are a number of conditions that the eye can suffer from. Most people will suffer as their lives go on from presbyopia - a loss of ability to change the power of the lens due to hardening of the lens tissues, leading to a lack of ability to focus on close objects, such as when reading.
Other common conditions that affect large numbers of people are:
The developing world has a number of different requirements for refraction methods compared to the developed world, for reasons including primarily the lack of trained optometrists, but also transportation difficulties, the scale of the issue, requirements imposed by a low level of education in many places and a lack of facilities and money.
Subjective refraction is the traditional refraction technique used by optometrists around the world. The process works by adjusting a corrective lens placed on the patient and querying the patient on how the changes affect their vision, using a variety of observation charts. From determining where a patient can read to on a visual acuity chart (either a 'letters' chart, or a split C or rotated E chart), this method is also used to determine a patient's visual acuity (e.g. 20/20 vision).
The process has been used and refined over many years, and achieves a high degree of accuracy statistically. The Centre has conducted work into examining the reproducibility of the refractions obtained through this method at UK optometrists, which can be found on our Research Publications page.
Subjective refraction has the advantage of being able to determine both sphere and cylinder (astigmatism) corrections, as well as being able to determine (with appropriate training) common eye diseases as part of the examination.
In many parts of the developing world there are difficulties with this approach; suitably trained professionals are needed to measure the prescription required and optical laboratories are expensive to set up and run. Neither of these are available in anything like the number available to meet the current need. Facilities that do exist are usually located in major cities meaning that the cost of access for many individuals, given the time and travel required, can also be prohibitive. As such although this approach can be effective, it is often beyond the reach of all but the wealthiest.
The challenge is to find an appropriate solution that will scale and perform well for the vast numbers of people lacking vision correction worldwide.