Cataract

According to WHO definition: "Cataract is clouding of the lens of the eye which impedes the passage of light. Although most cases of cataract are related to the aging process, occasionally children can be born with the condition, or a cataract may develop after eye injuries, inflammation, and some other eye diseases."

Globally, cataract (opacification of the lens) is the single most important cause of blindness, and cataract surgery has been shown to be one of the most cost-effective health-care interventions. Most cataract is related to aging and cannot be prevented, but cataract surgery and insertion of an intraocular lens are highly effective, resulting in almost immediate visual rehabilitation. In well-managed eye units, high-quality, high-volume surgery is possible, one ophthalmologist being able to undertake 1000–2000 or more operations a year, as long as there are adequate support staff, infrastructure and patients who are able and willing to access the facilities.

Current situation
There are estimated to be almost 18 million people who are bilaterally blind from cataract, representing almost half of all causes of blindness due to eye diseases globally. The proportion of blindness due to cataract among all eye diseases ranges from 5% in western Europe, North America and the more affluent countries in the Western Pacific Region to 50% or more in poorer regions. The main non-modifiable risk factor is ageing. Other frequently associated risk factors are injury, certain eye diseases (e.g. uveitis), diabetes, ultraviolet irradiation and smoking. Cataract in children is due mainly to genetic disorders. Visually disabling cataract occurs far more frequently in developing countries than in industrialized countries, and women are at greater risk than men and are less likely to have access to services.

The cataract surgical rate—the number of cataract operations per million population per year—is a quantifiable measure of the delivery of cataract surgical services (Annex V). It is meaningful, however,only when it includes all cataract operations performed in a country, including those in the private sector and during outreach, and when the population size and age structure can be defined. Cataract surgical coverage indicates the number of individuals with bilateral cataract causing visual impairment, who have received cataract surgery on one or both eyes, in other words, the proportion who were eligible for surgery and who received it. This indicator is used to assess the degree to which cataract surgical services meet the need. The data are obtained from population-based surveys or rapid assessments. Software for monitoring and assessing the quality of cataract surgery is available, and VISION 2020 encourages the monitoring of quality so that performance continues to improve.

There are two main surgical techniques for removing a cataract: extracapsular cataract extraction and phacoemulsification. In extracapsular cataract extraction, the lens capsule is opened and the nucleus of the lens and the cortex are removed, leaving the posterior capsule in place. This can be done through a small incision, which does not usually require sutures, or through a standard incision closed by removable sutures. In phacoemulsification, an ultrasound probe is used to fragment the lens, which is aspirated through a small incision.

There are three ways of correcting aphakia, an eye with a surgically removed lens: spectacles, contact lenses or an intraocular lens. Thick spectacles are required for patients who have undergone intracapsular extraction, and this technique was widespread in the past. Contact lenses are not appropriate in most settings. An intraocular lens, implanted after the cataract has been removed, is the optimal method, as it makes the use of thick spectacles unnecessary. Nevertheless, light spectacles are often necessary to compensate the loss of accommodation.

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