Centre for Vision in the Developing World

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, such as a lack of trained optometric personnel, 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 & money are other key issues to overcome.

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.

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

However, auto-refraction and auto-refractors have a number of disadvantages for the developing world:

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 eyeglass device that 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 identical 'universal' device enables enormous economies of scale, potentially allowing assembly in the nation it is to be deployed in.
There are some limitations to the technology - chief amongst these is that with currently available technology and devices astigmatism (where the amount of defocus varies depending on the rotational axis) cannot be corrected. Research is also underway to determine if the process is suitable for children.
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, with some of our publications available here.
We are currently investigating the applicability of self-refraction to children through the Child Self Refraction Study, and will soon be applying for funding to undertake studies into the accuracy and repeatability of self-refraction amongst adult populations.

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 Humanitarian and Civic Assistance (HCA) Program since 2000.

Retinoscopy

Retinoscopy is a method for determining refractive error that is often employed in the process of auto-refraction. A retinoscope shines light into a patient's eye and the optometrist (or in some cases auto-refractor) observes the reflection from the back of the eye (the retina). While moving the streak or spot of light across the eye's pupil the examiner observes the relative movement of the reflection then attempts to "neutralise" the reflection through placing lenses in front of the eye.

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).