WHO priority eye diseases
WHO
Childhood blindness
Childhood blindness refers to a group of diseases and conditions occurring in childhood or early adolescence, which, if left untreated, result in blindness or severe visual impairment that are likely to be untreatable later in life. The major causes of blindness in children vary widely from region to region, being largely determined by socioeconomic development, and the availability of primary health care and eye care services.
In high-income countries, lesions of the optic nerve and higher visual pathways predominate as the cause of blindness, while corneal scarring from measles, vitamin A deficiency, the use of harmful traditional eye remedies, ophthalmia neonatorum, and rubella cataract are the major causes in low-income countries.
Retinopathy of prematurity is an important cause in middle-income countries. Other significant causes in all countries are congenital abnormalities, such as cataract, glaucoma, and hereditary retinal dystrophies.
Magnitude
According to Gilbert and Foster, the prevalence of blindness in children varies according to socioeconomic development and under-5 mortality rates. In low-income countries with high under-5 mortality rates, the prevalence may be as high as 1.5 per 1000 children, while in high-income countries with low under-5 mortality rates, the prevalence is around 0.3 per 1000 children. Using this correlation to estimate the prevalence of blindness in children, the number of blind children in the world is approximately 1.4 million. Approximately three-quarters of the worlds blind children live in the poorest regions of Africa and Asia.
Prevention and treatment
Prevention and treatment of childhood blindness is disease specific. For Vitamin A deficiency, at a cost of only 5 US cents a dose, vitamin A supplements reduce child mortality by up to 34% in areas where Vitamin A deficiency is a public health problem. As vitamin A deficiency manifests often during an outbreak of measles, properly planned and implemented national vaccination programmes against measles has reduced the prevalence of eye complications.
In middle-income countries, retinopathy of prematurity (ROP) is among the leading causes of blindness, the incidence of which can be reduced through availability and affordability of screening and curative services. Early treatment of cataract and glaucoma can be beneficial, while low vision devices are helpful in children with residual vision.
The global childhood blindness programme
The Lions Clubs International Foundation, through their SightFirst Initiative is one of the major partners with WHO in addressing the causes of childhood blindness. Because of its extensive social and emotional burdens, prevention of childhood blindness is generally high on the agenda. The causes of childhood blindness, amenable to prevention and treatment, receive attention, not only because there are interventions available to handle these conditions, but also devastating consequences if not addressed.
Refractive errors and low vision
Refractive errors include myopia (short-sightedness), and hyperopia (long-sightedness) with or without astigmatism (when the eye can sharply image a straight line lying only in one meridian).
For low vision, the following two definitions are in use:
(WHO) Low vision is visual acuity less than 6/18 and equal to or better than 3/60 in the better eye with best correction.
(Low Vision Services or Care) a person with low vision is one who has impairment of visual functioning even after treatment and/or standard refractive correction, and has a visual acuity of less than 6/18 to light perception, or a visual field less than 10 degrees from the point of fixation, but who uses, or is potentially able to use, vision for the planning and/or execution of a task for which vision is essential.
Magnitude
Recent studies have confirmed the existence of a large burden of uncorrected refractive errors, although the interventions required are significantly cost effective, and have an important impact on economic development and quality of life. Severe refractive errors have been estimated to account for about 5 million blind people. According to the most recent data available to WHO, there are an estimated 124 million people in the world with low vision. About a fourth of these would benefit from low vision services.
Prevention and treatment
Refractive errors can be rectified with appropriate optical correction while people with low vision may be helped with low vision devices.
Diabetic retinopathy
Diabetic retinopathy is composed of a characteristic group of lesions found in the retina of individuals having had diabetes mellitus for several years. The abnormalities that characterise diabetic retinopathy occur in predictable progression with minor variations in the order of their appearance.
Diabetic retinopathy is considered to be the result of vascular changes in the retinal circulation. In the early stages vascular occlusion and dilations occur. It progresses into a proliferative retinopathy with the growth of new blood vessels. Macular oedema (the thickening of the central part of the retina) can significantly decrease visual acuity.
Magnitude
There are important differences over the past few decades in diagnosis, medical care, socioeconomic factors and other risk factors that influence the prevalence and geographic distribution of diabetes and retinopathy as well. It is estimated that in 2002 diabetic retinopathy accounted for about 5% of world blindness, representing almost 5 million blind. As the incidence of diabetes gradually increases, there is the possibility that more individuals will suffer from eye complications which, if not properly managed, may lead to permanent eye damage.
Prevention and treatment
Risk factors for diabetic retinopathy include duration of diabetes, level of glycemia, presence of high blood pressure, dependence on insulin, pregnancy, levels of selected serum lipids, nutritional and genetic factors. Medical interventions can decrease some of the risk to vision caused by diabetic retinopathy. The control of glycemia decreases the risk of the incidence and the progression of the retinopathy. If sight-threatening retinopathy is present, timely laser photocoagulation of the retina decreases the risk of a subsequent severe visual lesion.
VISION 2020 role
Diabetic retinopathy is on the priority list of eye conditions which can be partly prevented and treated. It is recommended that eye care services for diabetic patients be incorporated into strategic VISION 2020 national plans. In diabetic patients, regular examination of the fundus is essential, followed by appropriate laser treatment if required. Well tested international guidelines for management of diabetic retinopathy should be followed.
Glaucoma
Glaucoma can be regarded as a group of diseases that have as a common end-point a characteristic optic neuropathy which is determined by both structural change and functional deficit. The medical understanding of the nature of glaucoma has changed profoundly in the past few years and a precise comprehensive definition and diagnostic criteria are yet to be finalised. There are several types of glaucoma, however, the two most common are primary open angle glaucoma (POAG), having a slow and insidious onset, and angle closure glaucoma (ACG), which is less common and tends to be more acute.
Magnitude
The number of persons estimated to be blind as a result of primary glaucoma is 4.5 million, accounting for slightly more than twelve per cent of all global blindness. Risk factors are those limited to the onset of disease and those associated with progressive worsening in already established disease. The primary risk factors that are linked to the individual and the onset of the disease are age and genetic predisposition. The incidence of POAG rises with age and its progression is more frequent in people of African origin. ACG is the common form of glaucoma in people of Asian origin.
Prevention and treatment
There is little known about primary prevention of glaucoma; however, there are effective methods of medical and surgical treatment if the disease is diagnosed in its early stage. Through appropriate treatment, sight may be maintained; otherwise the progression of the condition leads eventually to severe restriction of the visual field and irreversible blindness.
VISION 2020 role
As the majority of cases of glaucoma can be effectively managed, it is desirable to include this condition in VISION 2020 national plans. This is particularly appropriate in countries and regions where some of the 5 principally targeted eye conditions are not a public health problem, and more resources and attention can be dedicated to this eye disease.
Age-related macular degeneration
Age-related macular degeneration (AMD) is a condition affecting older people, and involves the loss of the persons central field of vision. It occurs when the macular (or central) retina develops degenerative lesions. It is thought that circulatory insufficiency, with reduction in the blood flow to the macular area, also plays a part. Several forms of AMD exist.
Magnitude
Globally, AMD ranks third as a cause of blindness after cataract and glaucoma. It is the primary cause in industrialized countries. The main risk factor is ageing. Other risk factors may include the use of tobacco, genetic tendencies, the degree of pigmentation (with light coloured eyes being at higher risk), arterial hypertension, the ultraviolet rays, and consumption of a non-balanced diet.
Prevention and treatment
At present, the available evidence points to the relevence of smoking prevention and cessation as inducive to preventing incidence of AMD. As for the cure of the disease, there is at present no definitive treatment. Palliative treatments which are able to retard the progress of the disease include the use of intravitreous drugs, lasers, dynamic phototherapy and sometimes surgery.
The early beginning of rehabilitation for those with the disease includes psycological support, mobility and life skills to continue conducting a full life experience and face no limitations, as well as adaptation of the living and work places, and the use of special aids for reading and computer use.
WHO Role
WHO is working with an international expert panel to develop the most appropriate approach to the management of AMD in a Public Health framework, together with the other main chronic eye diseases.
Corneal opacities
Corneal visual impairment encompasses a wide variety of infectious and inflammatory eye diseases that cause scarring of the cornea, the clear membrane that covers the outside of the eye. Significant scarring ultimately leads to functional vision loss.
Magnitude
The 4th cause of blindness globally (5.1%), corneal blindness is one of the major causes of visual deficiency after cataract, glaucoma and age-related macular degeneration (AMD). Trachoma is responsible for nearly 4.9 million blind, mainly as a result of corneal scarring and vascularization. Ocular trauma and corneal ulcerations are significant causes of corneal blindness.
They are often underreported but they are estimated at 1.5 to 2.0 million new cases of unilateral blindness every year. Among the causes of childhood blindness (approximately 1.5 million cases in the world and 5 million children with visual impairment) appear xerophthalmia (350,000 cases per year), new-born conjunctivitis, and rarer ocular infections like herpes and keratoconjunctivitis.
Even though the control of onchocerciasis and leprosy are public health success stories, these diseases are still significant causes of blindness, affecting approximately 250,000 individuals each. Traditional eye medicines have also been implicated as a major risk factor in the current epidemic of corneal ulceration in developing countries.
Corneal visual impairment encompasses a wide variety of infectious and inflammatory eye diseases that cause corneal scarring, witch ultimately leads to functional vision loss.
Prevention and treatment
Public health prevention programmes are the most cost-effective means of decreasing the global burden of corneal blindness Indeed, the only currently available curative treatment is the surgery, by graft of cornea. But the access to this surgery is very difficult, even in the developed countries, for lack of donors.
Genetic eye diseases
Genetic eye diseases include a large number of ocular pathologies which have in common the transmission from parents to children by their genetic inheritance. All do not cause visual impairment.
Magnitude
Knowledge about genetic eye diseases has increased dramatically during the last twenty years. Although there are no global statistics which let us know the extent of the burden of visual impairment from genetic causes, it does seem that genetic eye pathology represents a significant percentage of the causes of blindness in industrialized countries.
Prevention and treatment
The only current means of prevention of genetic eye pathology is genetic counselling. Treatment of genetic eye disorders is largely experimental, with the exception of surgeries on the cornea, lens and vitreous, which are well-documented in certain cases. The best hopes for treatment, however, lie in the use of gene therapy, growth promotion therapies for degenerative diseases, and possibly the grafting of retinal cells.
