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

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.

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.

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.

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.

Problems

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.

Fluid-Filled Lens Technology

Fluid-filled lenses use the incompressibility of liquids to change the physical shape of the lens. The lens is constructed with two flexible membranes on the optical surfaces, held in place by a solid surround.

The power of the lens is changed by pumping fluid into or out of the central lens reservoir - less fluid causes the flexible membranes to bow inwards due to the reduced internal pressure, and more fluid causes the membranes to expand outwards, as shown in the diagram. This causes the lens to change refractive power, which makes it suitable for adjustable eyeglasses.

Advantages

• Simple actuation mechanism - pumping fluid from external reservoirs (e.g. a syringe)
• Suitable for fitting into spectacle frames
• Can be made to different sizes relatively easily
• Tough and durable if the membranes are hard coated or placed behind plastic covers
• The original Adspecs using fluid-filled lenses have been shown in clinical trials to give wearers clear vision

• Current lenses have a round shape; however, technology now in development will allow other lens shapes in future
• Astigmatism of the eye cannot presently be corrected

Electrowetting Lens Technology

Electrowetting lenses rely on the surface tension of liquids to produce their curvature. The walls of the electrodes in the diagram repel the conducting fluid - when the electric field is switched on the interfacial tension between the conducting fluid and the electrodes is changed, leading to a change in surface contact angle where they meet and thus a change in curvature of the overall lens system.

Advantages

• Very large range of lens powers available - often in the range of +/- 50-100 dioptres
• High speed alteration of lens power

• Difficult to manufacture in large sizes - limited to the range over which surface tension provides curvature and are thus unsuitable for glasses

Applications

Electroactive Lens Technology

Electroactive lenses rely on the principle that certain liquid crystals change their refractive index (and thus its refractive power) when an electric field is applied across them. By applying different types of electric field, different electroactive lens technologies can be used.

The top half of the above diagram illustrates one type of electroactive lens - in this case an internal element with (when deactivated) an identical refractive index to the surrounding material. When switched on, a fixed refraction is added to the overall lens, changing the overall power of the lens.

The bottom half of the diagram illustrates an alternative and more complex method - a varying electric field is applied across a liquid crystal element, causing the refractive index to vary across the surface. This is a 'graded index' lens, which bends light differentially depending on the refractive index that the light interacts with, focusing incoming beams to a point.

Advantages

• Very high speed power change - almost instantaneous
• Could be made thin and large enough to place into glasses
• No external reservoirs of liquid needed

• Currently difficult and expensive to manufacture

Alvarez Lens Technology

Alvarez lens systems are two lenses with special surface shapes - a cubic polynomial function. When moved relative to one another as shown in the diagram, the overall thickness of the combined lenses changes to produce different amounts of refraction and lens power.

Advantages

• Can be made cheaply and relatively easily
• Simple actuation mechanism
• Any shape possible - there are no restrictions on lenses being round

• Limited power range possible whilst keeping the lens thin - less than that of fluid-filled lenses
• A narrow central area of the lens has the correct power but the surrounding area gives distorted vision
• Alvarez lenses have not yet been clinically tested for use in glasses

Applications

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

• 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.

Auto Refraction

There are numerous automated methods of determining the required correction of a patient, which are grouped together under the term 'auto-refraction'.

Auto-refractors (devices that perform auto-refraction) come in two physical forms: handheld or static. Static auto-refractors are commonly seen in optometrists all over the world, mainly used as a screening aid or secondary check to subjective refraction procedures.

Numerous technical methods exist to determine the refractive condition of the eye: many auto-refractors use a variant of retinoscopy (see retinoscopy tab above). The accuracy of the technique, although not quite as good as subjective refraction, gives good agreement generally, with static auto-refractors giving better results than handheld auto-refractors, at the expense of a lack of portability or flexibility.

Applicability to the developing world

Handheld auto-refractors are currently being used in a number of developing world vision projects, with a high degree of success. Their advantages include:

• Relatively high accuracy refraction measurements, enough to perform screening and determine prescriptions within +/-0.5D
• Determination of both sphere and cylinder refractive errors
• No cultural barriers or educational difficulties to overcome
• Can be transported from location to location if hand-held

• Expensive capital costs are often difficult for small organisations and clinics to bear, leading to auto-refraction being based around 'vision-in-a-van' solutions
• Handheld instruments are the most practical for small vision projects, but are limited in accuracy, especially with children
• Training is still required in their usage, and screening must be done on a one-to-one basis

Self Refraction

One of the most promising solutions for the problems the developing world faces in vision correction is the process of self-refraction - in simple terms, the patient sets their own spectacles prescription.

The self-refraction process

The process of self-refraction is extremely simple and is applicable to any eyeglasses product the power of the lenses of which can be adjusted. It can be administered by people with basic training in the protocol for fitting and can be deployed with minimal equipment.

Advantages

Self-refraction is ideal for the developing world for several reasons:

• It greatly reduces the requirement for optometrically qualified personnel in nations that have limited access to them.
• There is very little specialised equipment needed for fitting; this translates into low capital costs for new clinics and the potential for mobile clinics in remote areas.
• The mass manufacture of a single 'universal' product enables enormous economies of scale, potentially allowing assembly in the nation it is to be deployed in.

Further Research

As a new technique, self-refraction is currently undergoing continual research to determine its clinical accuracy and applicability to different demographics. The Centre has led the way in research into this field.

Studies & Field Trials

Please see Research Publications for details on previous studies into self-refraction.

Self-adjustable glasses using the self-refraction technique have previously been deployed in field trials to over 30,000 people through both NFED (an adult literacy program of the Ministry of Education in Ghana) and the US military's Humanitarian and Civic Assistance (HCA) programmes since 2000.

Retinoscopy

The procedure can be undertaken with the eye both accommodated (focused on a close object) and focused on a distant object. It is mainly used in situations where a subjective refraction is not possible, for example with mentally handicapped people or in cases where the patient is unable to communicate with the optometrist.

Retinoscopy is limited by the same problems as subjective refraction if performed by an optometrist: it requires training and one-to-one screening, although as a principle it is increasingly being applied in auto-refractors (see auto-refraction tab above).

Traditional Eyeglasses

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.

Snap Together Eyeglass Kits

An alternative approach to the provision of traditional-style eyeglasses in the developing world is snap-together lens/frame kits or even complete, ready-made glasses in a range of powers. A selection of lenses in a range of powers is provided which can be fitted on-the-spot into frames which are also provided. Careful selection of the lens powers allows a large .

Advantages of this approach in the developing world include a much lower capital cost than the cost incurred by traditional lens grinding and optical labs, and that glasses can be built in the field. It enables low-cost local optometrists to set up, obtaining kit refill supplies when necessary. Vision correction can be provided by local non-governmental organisations (NGOs) as part of a local project at relative ease.

However, kits or ready-made glasses only solve one part of the challenge. There still remains the need to determine what prescription an individual requires. As such kits that rely on subjective refraction techniques are still limited by access to trained eyecare professionals, although by enabling on-the-spot correction they may still bring significant improvements in efficiency compared to having to use an optical laboratory. A lack of trained professionals is one of the major bottlenecks. If instead a kit is used with an alternative means of determining what correction is necessary, such as self-refraction, then it might be possible to develop an approach which can be scaled to the numbers required.

Donated/Second-hand Eyeglasses

Large programmes of donated glasses already run in the developing world, primarily through the Lions Club International. Although they have been quite successful at getting many eyeglasses onto people's faces, they are ultimately limited to the donation supply and the prevalence of donated prescriptions - for example it will be very difficult to match both sphere and cylinder measurements on one pair of glasses.

Donated eyeglasses are also tied to trained optometrists and often emergency aid efforts; they are not an easily scalable or sustainable solution for the developing world.

Adjustable Eyeglasses

Adjustable glasses can be used with all refraction techniques, and are particularly versatile when used with the process of self-refraction, enabling the patient to set his or her own best correction and then to keep and use that same pair of glasses with the adjusters either removed or locked. Alternatively, subjective or auto-refraction can be used, with the glasses set to the determined power by an optometrist in the field.

There are a number of different lens technologies available that can be used to make adjustable eyeglasses. CVDW takes a keen interest in this field, and has led the way in research into self-refraction and adjustable glasses generally.

Previous work has determined the suitability of adjustable glasses and the process of self-refraction for vision correction in the developing world, and research is ongoing in new self-refraction studies, and its applicability to children.

Advantages of adjustable glasses/adaptive eyewear for the developing world include a massive reduction in the need and level of trained optometric personnel, simplification and reduction in cost (due to large scale manufacturing) of products held by local vision clinics and other vision projects, and the ability to have large-scale distribution by people who do not have high-level optometric training.

There are a number of difficulties that need to be overcome however; with current technologies astigmatism cannot be corrected, and indeed it is unclear whether a self-refraction approach would be able to provide this level of correction. Extreme cases of myopia or hyperopia may fall outside the range provided by a 'universal' pair of eyeglasses, and a lack of education may provide difficulties in fitting and explanation of the concept for those unfamiliar with vision correction.

Contact Lenses

Sadly, however, there are a number of drawbacks to the application of contact lenses for use in the developing world:

• Many people do not like or feel comfortable wearing contact lenses
• There are much higher long-term care requirements that include consumable cleaning fluids and regular replacements
• Much greater ophthalmological care is required over the course of use
• High costs and lack of access to facilities for low-cost manufacture
• Contact lenses are not suitable for correcting presbyopia - users will still require reading glasses

Laser Eye Surgery

• LASIK surgery involves creating a thin flap on the eye's cornea, then folding it to enable remodelling of the tissue beneath it with a laser. The flap is repositioned and the eye then left to heal.
• PRK also involves reshaping the cornea, but the corneal flap created is removed and discarded, allowing the cells to regenerate after the surgery.