Three quarters of blindness in sub-Saharan Africa is due to five treatable or preventable conditions as Justin Sherwin explains
There is a disproportionate amount of blindness in Africa, which is home to 19.8% of the world’s blind but only 11.5% of the population. (1) In 2001, it was estimated that approximately 1% of the continent was blind, defined as bilateral visual acuity <3/60 in the better eye. (2) Precise estimates of the prevalence of blindness are difficult to generate, because such research requires large sample sizes, in order to achieve sufficient statistical power, and are expensive. A novel method, the rapid assessment of avoidable blindness (RAAB), is simple to administer, cost-effective, and has been successfully used in Kenya. (3)
There are many reasons for the importance in treating avoidable blindness. Firstly, the ability to see is a human right, and no one deserves to be needlessly blind. Most of Sub-Saharan Africa is afflicted with poverty, which is an independent risk factor for blindness and is also associated with reduced access to treatment. (4) In the absence of treatment, the cycle of poverty is perpetuated, and acts as a further barrier to socio-economic development. The World Health Organization (WHO) considers the alleviation of avoidable blindness as one of the most cost-effective health interventions. Globally, it is estimated that the VISION 2020 strategy can ultimately save more than $200 US billion.(5)
Through the collaboration of the WHO and the International Association for the Prevention of Blindness (IAPB), the VISION 2020: The Right to Sight Initiative recognised that more than 75% of the blindness in Africa is due to one of 5 treatable and/or preventable conditions. (5) These five conditions comprised cataract, glaucoma, trachoma, onchocerciasis and childhood blindness. Ocular leprosy no longer constitutes a major problem in Africa, but the HIV infection has changed the ophthalmic landscape in some endemic areas, with the emergence of ocular associated manifestations of HIV/AIDS. Other target disease areas for VISION 2020 are low vision, diabetic retinopathy, refractive error and age-related macular degeneration, but a discussion on these is beyond the scope of the article. VISION 2020 is the global initiative for the elimination of avoidable blindness by the year 2020, and has an international membership of non-government organizations (NGO’s), professional organizations, eye care institutions and corporations. The overall objectives of VISION 2020 are to identify and educate individuals and organizations about the causes of preventable blindness within a particular country and to provide sufficient resources to prevention, treat and provide rehabilition to those in need. (5)
Cataract is any opacity of the lens in the eye, and is the leading cause of blindness in the developing and developed world. (1) In Sub-Saharan Africa, the prevalence of bilateral blinding cataract is estimated at 0.5%. (2) Unfortunately, the incidence of cataract in the developing world far outweighs the numbers who are being treated surgically. (6) In Sub-Saharan Africa, the cataract surgical coverage (CSC), a measure of the distribution of cataract surgery to those awaiting surgery in a given time period, is poor. (7) In order to monitor the surgical output in a given community each year, the cataract surgical rate (CSR) is calculated. This is usually quoted in the number of operations performed per year, per million persons. In 1999, it was estimated that Africa had the lowest CSR in the world at 300 operations/ million/ year, with the highest CSR’s estimated to be in developed regions. (7)
At present, nearly all surgery performed uses the insertion of an artificial plastic lens following the lens removal, using either an intracapsular or extracapsular approach. Surgery using phaecoemulsion technology is now the gold standard for most cases of cataract surgery in the developed world, however, is rarely seen in Africa due to high cost and complexity required to use it. Access to the low-cost plastic intraocular lens device has improved dramatically due to the installation of lens factories in developing settings, including India and Eritrea. Treatment of cataract blindness is a priority of many eye care NGO’s because it is cheap, quick, effective and relatively simple. Before the widespread implementation of the intraocular lens, cataract surgery consisted of removing the cataract lens and wearing thick, plus powered glasses in order to deal with the resultant high hypermetropia (long-sightedness). Uncorrected or undercorrected aphakia (state when no lens is present within eye) continues to be a problem in some communities. ‘Couching,’ the unorthodox process of manually pushing the cataract lens into the posterior chamber of the eye, is common in some African communities, and can often result in serious ocular complications.
Barriers to ensuring that persons with vision-impairing cataract receive surgical care, include economic reasons, access to healthcare services, lack of knowledge about the surgery and psychological issues. Further efforts at reducing the surgical backlog should focus on training suitable personnel, improving existing healthcare services and creating new healthcare services, and increasing the availability of surgical equipment to areas in need.
The most common aetiology avoidable childhood blindness in Malawi has been shown to be corneal pathology due to Measles/ Vitamin A deficiency. (8) Some countries in Sub-Saharan Africa do not have such a problem with Vitamin A deficiency because of diets high in Vitamin A foodstuffs such as red bean oil. Other common causes of childhood blindness in Sub-Saharan Africa include ophthalmia neonatorum (due to chlyamydia or gonorrhoea infection), trauma, uncorrected refractive error, (congential or juvenile) glaucoma, trachoma, corneal scarring, cataract, trauma and genetic eye diseases. (7)
There are several mechanisms by which the burden of childhood blindness in Africa can be reduced. These include distribution of Vitamin A capsules at health clinics, measles vaccination, avoidance of harmful traditional medicine practices to prevent corneal disease, ocular prophylaxis to prevent neonatal conjunctivitis and the ‘SAFE’ strategy for trachoma eradication (see below), in addition to providing health education to parents.
Glaucoma is a heterogeneous group of conditions characterised by a ‘cupped’ appearance of the optic nerve and a corresponding visual field deficit that is typically, but not always, associated with elevated intra-ocular pressure. It is the second most common cause of bilateral blindness worldwide of whom more than 10% of which are considered to be blind.(1) Genetic factors play an important role in the aetiology of the disease, and the prevalence of glaucoma worldwide is highest in those of African descent. (9)
Detection of disease is hampered by lack of sensitive visual field machines in poor and rural settings, and other necessary diagnostic equipment such as slit lamp biomicroscopes with tonometers to measure the intraocular prssure. Patients are often asymptomatic before significant visual loss has occurred, which constitutes a considerable problem in resource poor settings. It may be advantageous to provide opportunistic screening for glaucoma, such as during refractive testing or at the time of ocular surgery for cataract. It is preferable to diagnose glaucoma as early as possible, because early diagnosis is associated with better visual outcomes. Even so, not all persons respond to treatment. Treatment for glaucoma includes medical treatment with ocular hypotensive therapy, surgical treatment that is typically a drainage operation (trabeculectomy) or laser therapy. In Sub-Saharan Africa, the use of ocular hypotensive therapy is restricted due to economic reasons and difficulties with compliance. Surgery is restricted due to cost and lack of trained staff, and laser therapy is restricted due to lack of available facilities.
Trachoma is the world’s leading cause of infectious blindness and is caused by repeated conjunctival infection with Chlamydia trachomatis, and is still prevalent in many countries in Sub-Saharan Africa. Trachoma affects about 84 million people worldwide of whom about 8 million are visually impaired. (10) It is more common in women and children, and typically associated with poor sanitation and hygiene. The present classification of trachoma outlined by the WHO comprises five categories. These are Follicular Trachoma (TF), Intense inflammatory trachoma (TI), Trachomatous scarring (TS), Trachomatous Trichiasis (TT) and Corneal Opacity (CO). Active trachoma is defined as either TF and/or TI.
WHO and the IAPB launched the “SAFE” strategy for Trachoma elimination. This strategy involves Surgery for trichiasis (bilamellar tarsal rotation procedure), Antibiotics (single oral dose azithromycin and tetracycline eye ointment), Facial cleanliness and Environmental improvements (increasing availability/quality of water, decreasing overcrowding, reducing density of flies and improving latrine access). Environmental improvements and antibiotic coverage also assist in the reduction of other infectious diseases, such as Guinea worm. In a critical review on SAFE, the highest support for its use was found in the ‘S’ and ‘A’ components. (11)
However, only limited supplies of tetracycline ointment and azithromycin are available for trachoma eradication in some countries in Sub-Saharan Africa, and the backlog of trachoma surgery is high in some areas. Yet, even when mass antibiotic treatment is not available, environmental and sanitary improvements have led to a reduction in trachoma prevalence in Malawi. (12) Surgery for trichiasis is widely performed by auxiliary ophthalmic personnel. The success of the SAFE strategy relies on donations of Zithromax (azithromycin) from Pfizer, as well as support from government and NGO’s.
Onchocerciasis, commonly known as ‘river blindness’ is disease caused by infection with the microfilariae Onchocerca volvulus that is transmitted via the vector Simulium yahense, a black fly. Globally, there are 37 million people affected, with majority in West, Central or East Africa, and approximately 300000 are blind from disease. (13) Apart from ocular pathology, infection with the microfilariae may also cause skin conditions and other systemic illnesses. Successful treatment of onchocerciasis lies with the administration of a once-a-year dose of the drug ivermectin, which is currently being provided at no cost to all those with this infection from Merck. However, there is emerging evidence that there may be some resistance to the side-effects of this potent drug. (14) Thus, the search for a second-line drug should be key to future management strategies. Also, efforts are underway to reduce the number of blackfly breeding sites through the spraying of larvae with chemicals. Unfortunately, a significant barrier to progress in the fight against onchocerciasis in West Africa has been political and civil unrest that has led to delayed access to treatment.
Tackling the problem
Important principles inherent to VISION 2020 include cost-effective disease prevention, management and rehabilitation interventions, infrastructure (human resources, healhcare facilities, technology, equipment) and funding. (5) These principles should be integrated into existing national healthcare systems and sustainable, equitable and of a high standard. World Sight Day, occuring annually on the second Thursday in October, ensures that members of VISION 2020 raise the profile of blindness as an important international public health issue. Expatriat British ophthalmologist Nick Metcalfe, performed an African continental record of 111 cataract surgeries on World Sight Day in 2006. Such feats give a glimmer of hope for the future of blindness eradication in Sub-Saharan Africa.
Sub-Saharan Africa has a decreased ratio of specialist ophthalmic staff compared to other developing settings, and of course, the developed world. (6) Furthermore, ophthalmologists undertake many different roles including program managers, research scientists and teacher. (2) In order to deal with the gross inadequacy of specialist ophthalmologists, auxiliary ophthalmic staff are crucial team members. For example, Kenya has cataract surgeons who are trained primarily in the treatment of cataract, and who do not have formal medical school training. Ophthalmic nurses, most of whom are able to perform surgery for trachoma, are numerous in Ghana and other countries. Furthermore, in Malawi, the presence of ophthalmic medical assistants has reduced the workload of specialist ophthalmologists, by assisting with cataract surgery. Refractionists are trained specifically in reducing the burden of refractive error associated visual impairment, a role that is partly supplied by optometrists in developed settings.
More than 10 years remains before the year 2020. Whilst the framework for successful blindness eradication of avoidable blindness in Sub-Saharan Africa has been paved, the widespread successful implementation of VISION 2020: The Right to Sight is far from complete. Considerable progress needs to be made before we can live in a world in which no one is needlessly blind.
Justin C Sherwin
Faculty of Medicine, Nursing and Health Sciences
Monash University VIC 3800
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