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The Two Minute Intro

The Two Minute Introduction

The Centre for Vision in the Developing World believes everyone, no matter where they are in the world, should be able to see. Over a billion people, according to the World Health Organization, would benefit from glasses but do not have access to them. But this is not an unsolvable problem. In this short series of slides, we'll introduce the problem, a solution, and ourselves.


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Self-adjustable glasses

CVDW's position statement

The Centre for Vision in the Developing World has a special research interest in the use of self-adjustable glasses in the developing world. Read below our position statement on their use.


The Centre for Vision in the Developing World (CVDW) recognises that uncorrected refractive error is a major problem and supports the aims of the global community in tackling it. CVDW recognises the efforts that the WHO and other bodies are making in their drive to provide effective, sustainable solutions to this problem around the world.

However, these efforts should be seen in the context of the unfortunate reality of current and likely future provision of eye care in many developing world nations: quite simply, the number and distribution of trained eye care professionals in these countries is far too limited to meet the needs of the people. Despite efforts to the contrary, hundreds of millions of persons around the world who require only a simple pair of eyeglasses do not yet receive even this modest provision of eye care. If we are forced to rely only on the conventional model of dispensing eyeglasses, this unfortunate situation will not change in the foreseeable future without an unprecedented and unlikely transfer of resources from rich to poor: one estimate for refractive error alone is $26bn per year, or $120 per person1 assuming a pair of eyeglasses lasts the desired three years.

CVDW believes that two mutually-related approaches, self-refraction and the deployment of self-adjustable eyeglasses, can help in meeting this simple need using relatively few resources.

Among its aims, CVDW:

  1. supports research into the efficacy of self-refraction in all populations and suitable age groups;
  2. supports research into the effective deployment of appropriate vision correction methods, including and not exclusively self-adjustable eyeglasses, in areas of the world that need refractive vision correction.
This statement is intended to set out CVDW's position with respect to self-refraction and self-adjustable eyeglasses.


Self-refraction: A method whereby a person seeks to achieve best-corrected vision following an appropriate protocol under the supervision of a trained individual and using suitable apparatus under his or her own control.

Self-adjustable eyeglasses: eyeglasses with a variable spherical power whose design allows for sphere power adjustment by the user whilst wearing the eyeglasses, typically as part of a self-refraction procedure.

Two different concepts

Self-refraction and self-adjustable eyeglasses are two distinct but related concepts. As such it is important to consider them to be separate tools with their own aspects.

Self-refraction promises two main benefits:

  1. A relatively quick method of determining refractive error that reduces the training requirements for personnel conducting refractions. This lowers one of the main barriers to deploying refractive eye care across many developing countries;
  2. The freeing up of clinical time to concentrate other areas.
Self-adjustable eyeglasses offer:
  1. A tool for use with self-refraction;
  2. A ready-made pair of eyeglasses that can be dispensed immediately after refraction (whether by self-refraction or conventional methods such as subjective refraction);
  3. Elimination of the delays and extra expense incurred when refractions and dispensing are conducted at separate locations;
  4. A very significant reduction in the logistical challenges and costs involved in supplying the many possible different powers of prescription lenses.

The research and application of self-refraction

Self-refraction, using self-adjustable eyeglasses, has been compared with conventional refraction methods in adults in a number2,3 of published trials. Research4 has also been conducted on the ability of teenage children to self-refract using self-adjustable eyeglasses. CVDW believes that the outcomes of the existing research justify the development and clinical trialling of improved such products, and the further development of efficient and effective distribution programmes for clinically proven products, including by way of larger-scale field trials.

Self-refraction has been used successfully around the world in a number of supervised deployments where tens of thousands of self-adjustable eyeglasses and reading glasses have been distributed to adults. Other deployments are planned for the near future as part of government-approved national programmes5.

CVDW does not condone or advocate the use of self-refraction methods in adults without appropriate oversight, or in children below the age of 13, at the present time.

The future of self-adjustable eyeglasses

Self-adjustable eyeglasses are still in their infancy compared with conventional glasses. Aside from their obvious potential benefits as a tool in the effort to tackle uncorrected refractive error, there may be for some people a number of further questions to be answered:


  • A legitimate concern for those running vision correction initiatives is the cost of self-adjustable eyeglasses in comparison with the relative proportion of programme funding available for eyeglasses. Appropriate design approaches and manufacturing methods can reduce the prices of such products towards the headline price of inexpensive off-the-shelf reading glasses.
  • Self-adjustable glasses offer indirect savings compared with conventional eyeglasses: they neither require dispensing facilities nor incur the delivery, travel or lost working time costs involved in getting a prescription for eyeglasses turned into a pair of eyeglasses in a patient's hands. Their deployment requires minimal training in comparison with that of a conventionally-trained eye care professional. These indirect costs may not be counted in the headline cost of a pair of eyeglasses but can be significant (see Smith et al1 for one estimate).
Aesthetic appeal or comesis
  • Early designs of self-adjustable eyeglasses are not generally recognised for their aesthetic beauty or styling despite efforts in nearly all cases to make the design as pleasing as possible. Their aesthetic design suffers from compromises caused by the infancy of the technologies used. This will be overcome as the technology matures.
Durability and standards
  • There is understandable concern about the robustness of designs which may feature fluids or apparently intricate adjustment devices. However, there are similar concerns about the durability of more conventional eyeglasses in harsh environments and extreme conditions. The solution in both situations involves appropriate design and evaluation of proposed products.
  • There is no reason why self-adjustable eyeglasses cannot be compatible with international manufacturing or safety standards.
Fixed interpupillary distance (IPD)
  • The human visual system has a good tolerance to mismatches in IPD (i.e. an IPD that does not exactly match that of a given patient) at moderate refractive powers. The precedents in this area are off-the-shelf reading eyeglasses and the deployment of ready-made eyeglasses (but not recycled eyeglasses) which may be supplied in standard frames. IPD differences are therefore likely to be only a minor concern in most cases.
Neglect of other medical conditions
  • Patients should have appropriate referral and follow up as part of any refractive error programme unless there is no possibility of this. Self-adjustable eyeglasses should be used in a way that is compatible with this aim. Indeed CVDW proposes that initiatives that include self-adjustable eyeglasses can help educate populations about eye care services and free up limited medical human resources for other conditions.
Unsuitability for inclusion in refractive error programmes
  • CVDW recognises that refractive error programmes should be designed to meet the needs of a particular situation or population as opposed to the constraints of a given product or procedure. Consequently, CVDW proposes that products such as self-adjustable eyeglasses should be designed to meet the needs of the programmes or initiatives in which they are to be deployed. Any design team would naturally seek to meet any relevant requirements such as cost and method of deployment. The aim would be one or more products whose use and deployment is flexible enough for programme managers to fit such products easily into their deployments. This could potentially be done in conjunction with a self-refraction element.
  • Self-adjustable eyeglasses offer a way to help bridge the gap between current levels of provision and more complete eye care services, to seed demand for prescription eyewear and, in time, to help to sustain these traditional eye care approaches.
CVDW believes that concerns about cost, durability and aesthetics as well as clinical and organisational concerns can be addressed by careful design, engineering and development of deployment and distribution methods, and clinicial trials of all new products. There are no known fundamental technical or organisational obstacles to the inclusion of self-adjustable eyeglasses in refractive error programmes.


  1. Smith, TST; Frick, KD; Holden, BA; Fricke, TR; Naidoo, KS, 2009, Potential lost productivity resulting from the global burden of uncorrected refractive error, Bulletin of the World Health Organisation, 87
  2. Douali, MG; Silver, JD, 2004, Self-optimised vision correction with adaptive spectacle lenses in developing countries, Ophthalmic Visual Optics, 24
  3. Smith, K; Weissberg, E; Travison, TG, 2010, Alternative methods of refraction: a comparison of three techniques, Optometry and Vision Science, 87:3
  4. He, M; Congdon, N; MacKenzie, G; Zeng, Y; Silver, JD; Ellwein, L, 2010, The child self-refraction study: Results from urban Chinese children in Guangzhou, Ophthalmology, in press
  5. Vision for a Nation, Rwanda
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The Problem

Global Facts

  • Refractive error is the greatest cause of low vision globally, and the second largest cause of preventable blindness after cataracts.
  • In the UK there is approximately one optometrist for every 5,000 people.
  • In Sierra Leone the ratio is 1 per 6 million - there is only one optometrist serving the entire country.

Quantification Research

CVDW has an active research interest in quantifying the number of people in need of vision correction worldwide and has a large refractive error database which we can use to study the need worldwide.

Millions of people all over the world wear corrective spectacles. Chances are that you do, or will have to in the future for reading and close work. But what if you did not have access to them, due to the cost or the lack of trained opticians who can determine the level of correction you need?

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.

We want to end this.

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.

Current methods of solving this issue have proven ineffective; a new approach must be found.

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Research Publications

The Centre maintains an active research programme and has had several studies that it has been involved with published in peer-reviewed journals. These journal articles are available to download on this page.

We also occasionally attend academic conferences to present recent findings, and these posters and presentations can be found lower down the page.

Published Papers


Global cost of poor vision

J. D. Silver, The Optician (2013)

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Read abstract...

British Medical Journal

Self correction of refractive error among young people in rural China: results of cross sectional investigation

M. Zhang, R. Zhang, M. He, W. Liang, X. Li, L. She, Y. Yang, G.E. MacKenzie, J. D. Silver, L. Ellwein, B. Moore, N. Congdon, BMJ (2011)

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Read abstract...


The Child Self-Refraction Study - Results from Urban Chinese Children in Guangzhou

M. He, N. Congdon, G.E. MacKenzie, Y. Zeng, J.D. Silver, L. Ellwein, Ophthalmology, Vol 118 (2011)

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Read abstract...

Ophthalmic and Physiological Optics

Self-optimised vision correction with adaptive spectacle lenses in developing countries

M. G. Douali and J. D. Silver, Ophthalmic and Physiological Optics, Vol 24 (2004)

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Read abstract...

South African Optometrist

How to use an adaptive optical approach to correct vision globally

J.D. Silver, M.G. Douali, A.S. Carlson and L. Jenkin, South African Optometrist, Vol 63 (2003)

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Read abstract...

International Agency for the Prevention of Blindness

Vision correction with adaptive spectacles

G. D. Afenyo and J. D. Silver, in World Blindness and its Prevention, vol. 6, ed. Pararajasegaram and G. N. Rao, p. 201-208 (International Agency for the Prevention of Blindness, 2001)

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Read abstract...

Posters and Presentations

Second Oxford Conference on Vision for Children in the Developing World

An Introduction to Self-Refraction

J.D. Silver

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American Academy of Optometry, October 2011, Boston

The Boston Child Self-Refraction Study

B., OD, C., OD, S. Lyons, OD, N. Quinn, OD, P. Tattersall, DipPharm, MSc, J.D. Silver, Dphil, D.N. Crosby, DPhil, M. He, MD, L. Elwein, PhD, G. MacKenzie, Dphil, N. Congdon, MD

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Vision UK 2009, London

Estimating the Global Need for Refractive Correction

J.D. Silver, D.N. Crosby, G.E. MacKenzie, M.D. Plimmer

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Adaptive Optics 2008, London

Vision Correction in the Developing World: Perhaps the largest application of Adaptive Optics?

D.N. Crosby, M.G. Douali, G.E. Mackenzie, M.D. Plimmer, R. Taylor, J.D. Silver

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IAPB 8th General Assembly, Buenos Aires

The Global Need for Refractive Correction

J.D. Silver, D.N. Crosby, M.G. Douali, G.E. Mackenzie, M.D. Plimmer

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ICEE World Conference on Refractive Error and Service Development, Durban

Repeatability and reproducibility of self-refraction using continuously adjustable fluid-filled spectacle lenses in pre-presbyopes

G.E. Mackenzie, J.D. Silver, D.N. Crosby, M.J.A. Newbery, A.K. Robertson

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The Centre hosts occasional conferences to discuss matters surrounding vision correction, inviting and hosting many of the world's leading experts in refractive error, developing world vision correction and global development.

Past conferences have been organised in conjunction with the World Bank and the Partnership for Child Development.

March 2011 - BMJ Innovation Expo

Panel discussion:
An expert guest panel comprising NHS medical director, Bruce Keogh; founder of Medical Futures, Andy Goldberg; and science journalist Vivienne Parry debated four medical innovations selected by BMJ clinical adviser, Ashley McKimm.

The panel identified Josh Silver's self-adjustable glasses as the idea most likely to make the biggest impact on healthcare by 2020.

View the BMJ video on self-adjustable eyeglasses →

April 2011 - Second Oxford Conference on Vision for Children in the Developing World

Conference Aims:
The Second Oxford enabled expert discussion on the implications of the CSRS by development specialists, academics, child vision experts, non-governmental organisations and representatives of the private sector. The Conference presented the results of the CSRS to and facilitated discussion on their implications.

The Conference then explored the potential for the wider application of self-refraction using adjustable spectacles and other appropriate vision technologies to children in the developing world and agreed next steps for further development.

View the conference declaration →

July 2007 - Vision for Children in the Developing World

Conference Aims:
Combating child visual impairment is an essential step towards the global movement of achieving Education for All by 2015 within the framework of the Millennium Development Goals. In recognition of the importance of child vision, a three day expert meeting of national and international collaborators is being held. The meeting will establish international collaboration between vision specialists towards providing vision correction to school-age children in the developing world.

Representatives from the scientific community, donors, NGOs and the private sector will review the need for the provision of affordable vision correction to children across the developing world, review sustainable protocols for the collection, analysis and dissemination of refractive data and propose an action plan to implement key recommendations.

View the conference materials →

August 2004 - Affordable Vision Correction Conference

Conference Aims:
Approximately 1/5 of the world population needs vision correction, still not one national plan includes affordable vision correction. This problem can not be tackled unless we find affordable vision correction methods.

This conference aims to gather representatives from governments, NGOs, faith-based organizations and the private sector to discuss different approaches for the provision of vision correction across the world as well as to identify and review the options available.

View the conference materials →
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Lens Technology

One of the key components for self-refraction are adjustable lenses (also known as adaptive optics, adaptive eyewear or adaptive eyeglasses): lenses the refractive power of which can be changed. Traditionally this is accomplished by moving sets of lenses relative to one another along an axis (such as in camera lenses). However, this is not practical for applications such as eyeglasses.

This page contains information on various adjustable (or adaptive) lens technologies that are suitable for application to spectacles for the developing world.

Click through the tabs below to discover more about adjustable lens technologies.

The Eye - the original adjustable lens

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:

  • Myopia: (short-sightedness) Rays of light from a distant object are focussed in front of the retina. Myopia occurs either because the eye is too long or the refractive elements (the cornea and crystalline lens) too powerful to produce a clear image at the retina.
  • Hyperopia: (long-sightedness) Rays of light from a distant object are focussed behind the retina, either because the eye is too short or because the refractive elements of the eye are not powerful enough to bring an image into focus at the retina.
  • Astigmatism: Astigmatism occurs when the curvature of any given refractive element of the eye differs across its surface (i.e. the lens in the eye is shaped more like a rugby ball than a football). This lack in uniformity across the surfaces of the eye's refracting elements prevents it from producing a sharply focused image at the retina. Astigmatism usually produces an image that is more defocused in one direction than another.
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Frequently Asked Questions

What does CVDW do?

The Centre for Vision in the Developing World studies the clinical and practical issues in providing vision correction to people who currently lack access to it. We research and develop effective, sustainable and clinically-validated approaches to the correction of refractive error in developing world populations.

What is CVDW's position on self-adjustable glasses?

We have a strong research interest in self-refraction and self-adjustable glasses, and we believe they are an effective way to tackle the lack of access to vision correction in the developing world. Read our full position statement by selecting it from the Research main menu.
Read position statement →

Does CVDW distribute adjustable glasses?

As part of our research studies and clinical trials, we undertake small-scale distribution in the developing world.

Am I able to buy a pair of adjustable glasses?

At present, CVDW supplies adjustable glasses only to its research and distribution partners for the purposes of clinical and field trials.

Am I able to donate to CVDW and receive a pair of adjustable glasses?

At present, as adjustable glasses are not available individually, we are unable to provide glasses in exchange for donations.

What conditions do the adjustable glasses treat?

Adjustable eyeglasses are designed only to work for the same conditions that normal eyeglasses work for. They do not prevent or reverse macular degeneration or any ophthalmic condition other than spherical refractive error (myopia and hyperopia; also presbyopia).
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Refraction Methods

A vital part of correcting vision is the process of refraction - determining the level of correction that a patient requires (refractive error) and diagnosing their condition (e.g. hyperopia, myopia, presbyopia etc.) For more information on the different refractive conditions of the human eye, click here.

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.

Click through the tabs below to discover more about refraction techniques.

Subjective Refraction

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.

Applicability to the developing world

Subjective refraction, although the ideal solution for nearly everyone requiring corrective aids to vision, is currently difficult to practice in the developing world and would be unable to correct the one billion people who need vision correction. The technique is unsuitable for a number of reasons:
  • It requires trained optometrists undertaking one-on-one screenings: there are currently far too few optometrists in the developing world, and healthcare costs put them out of reach of most of the population.
  • The capital costs of training and equipping an optometrist are very high, prohibitive for many.
  • Dedicated facilities are often required in the form of vision clinics and practices.
  • Language and communication difficulties can often arise in the process, especially if the optometrists are not from the local area or nation.
Ultimately, although subjective refraction in the developing world is a long-term ideal, at present it is unsuitable due to its lack of scalability and need for resources that are lacking in the developing world.
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Correction Methods

Once the patient's refractive error has been determined, there are various methods of correcting vision to give 20/20 or better visual acuity. This page discusses their relative merits and attributes when applied to the problem of vision correction for the developing world.

Click through the tabs below to discover more about correction methods.

Traditional Eyeglasses

In the developed world, eyeglasses are usually obtained through optometrists' practices, and the correction prescription they determine through subjective refraction is sent to an optical laboratory, where lenses are ground to the correct refractive power and cut to the correct shape to fit into frames.

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.