Low Vision and Refractive Errors
Refractive errors (myopia, hypermetropia, astigmatism, and presbyopia) result in an unfocussed image falling on the retina. Uncorrected refractive errors, which affect persons of all ages and ethnic groups, are the main cause of visual impairment. They may result in lost education and employment opportunities, lower productivity and impaired quality of life. Services should focus on children, the poor and adults over the age of 50 years, and the correction provided must be affordable, of good quality and culturally acceptable. Services for refractive errors should be integrated at all levels of eye-care provision, including outreach. Assessment of individuals who have refractive errors, particularly those aged 50 years or above, provides an opportunity for identifying other potentially blinding conditions before they cause visual loss (such as glaucoma and diabetic retinopathy).
There are estimated 153 million people with visual impairment due to uncorrected refractive errors (2006), i.e. presenting visual acuity <6/18 in the better eye, excluding presbyopia. Globally, uncorrected refractive errors are the main cause of visual impairment in children aged 5–15 years. The prevalence of myopia (short-sightedness) is increasing dramatically among children, particularly in urban areas of South-East Asia. It has been found in almost 20% of school going children of higher socioeconomic status in Kathmandu, Nepal. The most frequently used options for correcting refractive errors are: spectacles, the simplest, cheapest and most widely used method; contact lenses, which are not suitable for every patient in Nepal considering the local condition; and corneal refractive surgery, which entails reshaping the cornea by laser.
The steps in the provision of refraction services are:
- Case detection: identification of individuals with poor vision that can be improved by correction;
- Eye examination: to identify coexisting eye conditions needing care;
- Refraction: evaluation of the patient to determine the correction required;
- Dispensing: provision of the correction, ensuring a good fit of the correct prescription; and follow-up: ensuring compliance with prescription and good care of the correction, repair or replacement of spectacles if needed.
The Vision 2020 global initiative intensively promotes awareness of the extent of uncorrected refractive errors and the means for correcting them. Uncorrected refractive errors are increasingly being addressed in national plans for the prevention of blindness, and low-cost, good-quality spectacles are becoming available. In 2003, a WHO working group reviewed the current classification of visual impairment and blindness and made recommendations for the revised version of the International Classification of Diseases (ICD). It recommended that the definitions of ‘blindness’ and ‘low vision’ be amended and that the term ‘presenting visual acuity’ be substituted for ‘best-corrected visual acuity’, as the latter does not allow an estimate of the contribution of under corrected refractive error to the visual impairment.
Eye screening programme of school going children is one of the regular activities conducted in the eye hospitals of Nepal NetraJyotiSangh. Usually, visual acuity test is performed at schools and those with poor vision are advised to go for refraction checkup in hospitals. Study shows that only 28% of those children detected with visual impairment due to refractive error and advised for glasses obtained the glass in a year follow up. The main reasons for not obtaining glasses were due to unavailability and the cost of glasses. Since there is no systematic approach in this school health programme it is difficult to assess the coverage and impact. At present the NNJS programme offers service to more than 200,000 school going children for visual acuity test and approximately 10,000 specs are distributed in these children every year.
- insufficient data on the prevalence and types of refractive errors in different populations and age groups;
- Lack of qualitative research on the impact of refractive errors on quality of life, visual function and economic productivity;
- Insufficient evidence about the most cost-effective ways of delivering refraction services in different settings; and
- Under estimation by health-care providers and policy-makers of the extent and potential socioeconomic impact of uncorrected refractive errors in the community.
- To eliminate avoidable visual impairment due to uncorrected refractive errors and reduce the magnitude of uncorrected Presbyopia
- To provide refraction and optical dispensing services that have a high success rate in terms of visual acuity and improved quality of life and are affordable, of good quality and culturally acceptable, to rural as well as urban populations.
- Establish comprehensive eye-care services, so that refraction services with provision of suitable correction tools are available at all levels, including during outreach activities.
- Train human resources to ensure that high-quality refraction and optical dispensing service are available where needed.
- Improve public awareness and generate demand for services through community-based initiatives, primary eye care and school eye-health programmes.
- Specifically in low-income settings, provide spectacles that are new, of good quality, accessible and affordable.
- Preschool vision screening programme are to be promoted to reduce the amblyopia due to refractive error.
- Vision screening and identification of refractive error are to be provisioned at community, health post and sub health post level.
- Refraction and optical dispensing service needs to be provisioned at constituency level.
- In order to smoothing the supply of affordable and quality optical material glass manufacturing unit will be developed at central and regional level.
- Assess the prevalence of refractive errors where data are lacking, and explore the optimal means of delivering services that are acceptable and cost effective.
Globally, it is assumed that approximately 18% of population are vision impaired which can be improved to normal with correction. This figure also includes the Presbyopia. In Nepal Mechi survey (1997) found that the prevalence of refractive error among the children of 5 to 15 years age group was 3% among the rural children. The survey conducted in 2008 among the same age group of higher SES community at Kathmandu shows the prevalence of 20%. The prevalence of Presbyopia was found to be 58.8% among the age group 35 years and over. In the basis of these findings it has been assumed for Nepal that approximately 15% of the population would require glasses to have normal distance and/ or near vision.
- Achieve a ratio of one trained functional refractionist per 75,000 population by 2015 and 1:40,000 by 2020.
- Comprehensive eye care services should ensure that refraction services with provision of suitable correction tools are available at all levels of service delivery, including community outreach activities.
- Particular attention should be paid to children of primary and secondary school age, the working poor and adults over the age of 50 years.
- The correction provided should be affordable, of good quality and culturally acceptable.
- Epidemiological research should be conducted on the prevalence of uncorrected refractive errors and its trends.
- Proportion of people with uncorrected refractive errors that cause visual impairment (i.e. presenting with visual acuity < 6/18 in the better eye)
Low vision services are aimed at people who have residual vision that can be used and enhanced by specific aids. Low vision is currently defined as ‘visual acuity of <6/18 down to and including 3/60 in the better eye’, from all causes. Many such persons require cataract extraction or refraction services.
In 1993, at WHO meeting in Bangkok, Thailand, the following definition was agreed on to identify persons who could benefit from low vision services: “A person with low vision is someone who, after medical, surgical and/or optical intervention, has a corrected visual acuity in the better eye of <6/18 down to and including light perception or a central visual field of < 20 degrees, but who uses or has the potential to use vision for the planning and/or execution of a task.” To prevent confusion in this document, when this second meaning of the term ‘low vision’ is intended it will be referred to as ‘functional low vision’ or it will be used in the context of low vision services. The definition of ‘functional low vision’ can be used in population-based surveys to determine prevalence and causes, although some persons with a corrected visual acuity of 6/18 or above in the better eye might benefit from low vision care.
Currently, there are no global estimates of the number of people with functional low vision. It is likely, however, to be 40–65 million. The number of people with low vision will increase as a result of the ageing of the world’s population, and age-related macular degeneration, glaucoma and diabetic retinopathy are increasingly important causes of low vision. Low vision services are not available in many countries, particularly developing countries, or are located only in major cities. It is estimated that less than 5% of people needing low vision care have access to it, but there is considerable variation between different geographical regions.
Vision 2020 intensively advocates for increased awareness of the need for low vision services, and courses to train national focal persons in low vision programme management have been conducted in four regions. These persons are then responsible for working with national Vision 2020 committees to ensure low vision services. A low vision resource centre is operating from Hong Kong, Special Administrative Region, China, to distribute high-quality, affordable low vision devices and equipment to all regions. Low vision services have been set up in some tertiary paediatric eye centres and often serve as national models; however, they can provide services only up to their capacity.
Low vision programme is already initiated in Nepal in 2005 at national level. The programme focused in capacity building of existing eye hospitals and primary eye care centres by providing training and LV devices. A national level device bank has also been established. Coordination between different stake holders such as eye care, educational sector and CBR has been initiated.
- Provision of low vision services is generally less prioritized by eye-care providers because of the low economic gain.
- The need for low vision services is often not fully recognized, owing to inadequate epidemiological data on the prevalence and causes of functional low vision. This information is needed for planning services.
- There is little evidence for the cost-effectiveness of low vision care interventions.
- Persons with low vision are often unaware that they can be helped.
- Communication and referral between eye-care, special education, rehabilitation and low vision services are often inadequate.
- in national Vision 2020 plans, planning for low vision services is inadequate.
- To enhance vision-related quality of life for people with functional low vision.
- To increase awareness about low-vision care among eye-care professionals and persons with functional low vision
- To provide evidence on the prevalence and causes of functional low vision
- To establish comprehensive low vision care for children and adults
- To provide evidence for the impact of low vision services on quality of life and barriers to access to low vision services and
- To increase proper coordination among different stakeholders involved in low vision care
- Advocate for the inclusion of low vision care as part of eye-care, education and rehabilitation services, and for awareness about low vision and low vision services in the community and among health, education and rehabilitation professionals.
- Include low vision in the curriculum of ophthalmologists, and other cadre of ophthalmic personnel and special school teachers of integrated schools.
- Mentor the activities of national focal person.
- Disseminate the existing curriculum and materials for training primary and secondary level personnel.
- Establish or promote low vision services in tertiary and secondary level eye care centres.
- Establish networks with other global campaigns, such as those of the International Council for Education of People with Visual Impairment and the World Blind Union.
- Summarize existing evidence and conduct research on the best practice for the provision of low vision services, their impact on life and limitations to their provision and uptake.
- Document existing effective models of comprehensive low vision care at primary, secondary and tertiary levels of eye care in both developed and developing countries.
- Arrange for transfer of knowledge to countries to encourage the establishment of new programmes.
- Establish regional low vision resource centres, as required.
- Promote use of good-quality low vision aids, such as those provided by the low vision resource centre in Hong Kong.
- Promote the development of high-quality, low-cost low vision devices to increase access.
In RAAB survey conducted in different zones of Nepal, it has been revealed that 0.4% of adult population are having low vision (based on functional definition). The low vision programme of Nepal reported that the numbers of children are 50% of total low vision clients who received service under the programme in last five years. So it seems that the problem is equally distributed in both adult and children population. The programme has also reported that 75% of total LV clients could be helped with LV devices or with microscopic glasses. Based on these assumptions, the targeted output for low vision services has been calculated and listed in Annexure (Table 32) and other targets to be met by 2020 are as follows:
- National Vision 2020 plan has been incorporated low vision services.
- Establish at least one low vision resource centre by 2015 and expand the provision with a target of one tertiary low vision service at least one per development region, by the year 2020.
- Examine all children in schools and in services for vision-impaired children for the need for low vision devices, and assess whether referral will be required for rehabilitation or educational services.
- Have functioning low vision clinics in all tertiary child eye-care centres with trained eye-care professionals.
- Provision of basic low vision clinical assessment facility and availability of devices in all primary eye care centres.
- Complete national focal person training courses, with refresher training and mentoring.
- Equip tertiary, secondary and primary low vision services according to the Vision 2020 standard list.
- Have at least five (one in each development region) low vision resource centres in operation by 2015.
- Number and percentage of low vision services at tertiary level that have equipment that meets or exceeds the Vision 2020 standard list requirements;
- Number of primary, secondary and tertiary eye care services providing comprehensive low vision services.
- Number of LV resource centres established and number of clients benefitted with it.
- Number of persons with functional low vision who have access to low vision services.