Global Blindness course: Understanding refractive error


Welcome to this presentation
on managing refractive error. By the end of it, you should be
able to define refractive error and describe its epidemiology,
explore considerations for service delivery
at the community level, and to appraise school
health programmes and their management. Refractive error in the
public health context is defined as a
presenting visual acuity of less than 6/18,
which can be corrected by refraction or by pinhole. Correctable myopia is defined
as worse than minus 1 dioptre. Correctable hyperopia is defined
as plus 3 dioptres or more. And it is essential to correct
an astigmatism of 1.5 dioptres or more. The patient’s
presenting visual acuity is categorised using the
World Health Organisation’s International
Classification of Disease. Uncorrected refractive error
is the second major cause of blindness and low vision
in the world after cataract. Estimates from 2004 indicate
that over 8 million people are blind and 145 million are
visually impaired because they lack refractive correction. Who is most affected
by refractive error? In children aged under 15, the
prevalence of refractive error has been found to be
higher in urban areas than in rural settings. This is possibly due to
a direct cause and effect relationship between access
to education and myopia. Refractive error amongst 94
million people aged over 50 includes cataract-related
index myopia or even uncorrected aphakia. The largest burden of refractive
error is in India and China. And more research is
needed about how and where to identify and treat people
with uncorrected refractive error. Some estimates for
service coverage shows that urban settings have
better services, particularly for children. Why is there so much
uncorrected refractive error? Many settings lack vision
testing for children to insure early
detection and management. There is a lack of
refractive services and limited affordability
of spectacle correction, particularly in
rural communities. Sometimes spectacles
are not regarded as an essential
medical intervention. And lastly, there may be
cultural disincentives, which means that people
choose not to wear or accept correction, especially girls. Visual impairment
from refractive error impacts both
individuals and society leading to limited educational
performance and success amongst children, social
isolation and fewer opportunities for
work and education, more exposure to morbidities
and higher mortality rates, and generally a lower
quality of life and poverty. There are two strategies
for improving access to comprehensive
community-based eye care. Static and outreach. Ideally, services are planned
for a population of 50,000. And they focus on increasing
demand and supply. At a primary level, ophthalmic
assistants or nurses can be trained to perform eye
examinations and refraction. To minimise referrals, they
can also be trained to dispense spectacles directly. Due to the lack of
evidence, we have to use estimates to guide
development of refractive error services. Estimating the
demand for spectacles can be calculated from
prevalence data for the target population or from
similar settings. Where no data is available,
20% of the total population is a reasonable estimate. Understanding the demand
allows planners and managers to appropriately allocate
refraction and dispensing equipment and
spectacles, as well as numbers of trained personnel. Social marketing of
refraction services has been a successful model
in creating demand and raising awareness. And this has been particularly
successful in India through vision centres. School health programmes aimed
particularly at the early teenage group have also
been shown to be effective. Targeting younger,
economically active groups in the workplace or
colleges is another option. In the over 50 age group,
health promotion and access to services will
also improve uptake. Refraction equipment and
spectacle dispensing equipment are both necessary to deliver
comprehensive services. A range of lenses and frames
suitable for local preferences must also be
stocked, particularly for children and girls. Equipment and
consumables are managed using an inventory and
a reliable supply chain. The priority age group
that needs vision testing at least once is children
aged 12 to 14 years. This is to detect
myopia of puberty. Younger age groups are tested
if resources are available. Each eye is tested and vision
less than 6/12 in either eye is defined as a case for
referral and further testing. Lower cutoff of less
than 1 dioptre correction often results in poor
adherence to spectacle wearing amongst children. In some settings,
schoolteachers can be trained to do an
initial visual assessment within the school. Teachers are provided with a
vision kit, referral protocol, and support from local
optometry services. In school vision
testing programmes, recruiting science teachers
who can explain the benefits to parents are an ideal choice,
as are teachers who wear spectacles as they will have
an understanding and empathy for a refractive error. The teachers must have the
support of school authorities. The process of vision testing
is made as simple as possible. Key points to remember
are the teachers must all be trained
and supported. Test each eye. Children that fail the
6/12 visual acuity cutoff must be referred using
an agreed method. Train teachers to refer
each case they identify. All the testing and referral
information should be recorded for monitoring and
evaluation of the programme. Children who are
prescribed spectacles should also be followed
up between 3 to 6 months. And lastly, support
and counselling must be provided to
parents and children. Management collect data to
monitor school vision testing programmes in order
to know the coverage. This is the number of
children whose vision has been tested by the teachers. Know the uptake of referral. This is how many of the
referred children actually present to optometrists. Establish how effective
the teacher’s testing is. If there are too
many false referrals, retraining may be necessary. And understand the acceptance
of refractive correction. This is achieved by revisiting
the school 3 to 6 months later and identifying which
children are still using their spectacles. Let’s look at monitoring in
more detail using an example. There are 5,000 children in the
district schools age 12 to 14, and 3,000 of them
undergo vision testing. To calculate the
coverage of services, we divide 3,000 by 5,000
and multiply by 100 to get a percentage. This gives us a 60% coverage. 110 children are referred
for refraction and 75 of them present to the optometrist. To calculate the uptake
of vision testing, we divide 75 by 110
and multiply by 100. This gives us a 68%
uptake of the service. 55 children out of
the 75 that presented are referred on to be
prescribed spectacles. The percentage of correct
referrals by teachers is calculated by dividing 55
by 75 and multiplying by 100. This gives a 73%
correct referral rate. This is good, but we
should also establish why all the children did not come. 40 children are still
wearing their spectacles three months later. To work out the acceptance
rate, we divide 40 by 55 and multiply by 100. And this gives us a
73% acceptance rate. This data can be monitored
on a monthly basis and used by management to adjust
the intervention appropriately. Vision testing in schools
is simple to conduct and can have a huge impact on
children and their education. Services need to be planned
with adequate resources, good monitoring and
management, and supported by effective communication
between schools and optometry services. In conclusion, refractive error
is the second most important cause of visual impairment
and blindness globally. Correction is relatively
simple and the challenges are in access,
affordability, and acceptance of spectacle correction. To meet the need,
comprehensive service delivery at the community
level is essential. And school vision testing
is an important strategy to address refractive
error needs in children, and it can be done by
trained and willing teachers.

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