Lens abnormalities may be divided into two categories - abnormalities of lens size and shape, which are largely developmental, and abnormalities of lens clarity, or cataract.

A cataract is essentially an abnormality in lens clarity, which can lead to impaired vision or even absolute blindness. It is one of the most common ailments affecting people (particularly aged people) worldwide. There are several factors contributing to the cause apart from age such as exposure to ultraviolet light, smoking and alcohol, genetic composition, and diabetes. Studies on the biochemistry and normal physiology of the lens and the changes that induce cataract formation continue.

An effective method, which could restrain the formation of a cataractous lens, has yet to be developed. However, normal visual function can be restored by cataract surgery which involves applying an artificial intraocular lens.

Developed countries throughout the world allot a significant portion of their health care budgets for cataract surgery. The United States makes a huge annual expenditure on cataract-related services. The scenario in the developing world is quite miserable – the numbers of new cataract cases significantly outnumber the rate of surgical removal. In Africa, not even half of the cases of cataracts each year have their sight restored surgically.

Definition

Cataracts can be defined as an eye disease in which the crystalline lens or its capsule becomes opaque (cloudy). Its effect on the vision may be incontrovertible or convertible. It eventually results in loss of vision.

There are various causes of cataract development, which include metabolic disorders, developmental abnormalities, trauma and drug-induced changes. The major cause of visually evidential cataracts is ageing. As we grow old the lenses in our eyes deteriorate. For some, cataract development occurs.

Classification of Cataracts

The cause of age related changes in the lens due to cataracts has not been explored fully but it is expected to be multifactorial. There are three main classifications of age-related cataracts defined according to their clinical appearance: cortical, nuclear, and posterior subcapsular.

Cortical

With cortical cataracts new lens fibers are formed on the cortex of the lens. These fibers are not wasted with ageing and new fibers continue to grow forming a layer on outer portion of the lens, under the outer coating or capsule of the lens. Ageing causes discrete opacities (cortical spokes) within the cortex of the lens. There are no visual problems until they affect the visual axis or the entire cortex, as the lens becomes white and matures.

Nuclear

The nucleus of a lens is compressed with aging and becomes harder (nuclear sclerosis cataract). This type of cataract is associated with yellowing of the lens. This progresses gradually over the years. It certain cases the affected person experiences a change in refraction (myopic shift) which is often referred as second sight, as he/she does not usually require glasses for reading. However, with further progression there can be a loss of vision, especially for near vision.

Posterior subcapsular

Occurrence of granular opacities primarily in the central posterior cortex causes this type of cataract. It is generally more common in younger patients. Affected patients suffer symptoms such as complaint of glare when driving at night and reduction of near vision acuity more than distant vision.

Factors responsible for cataracts

The epidemiological studies suggest a number of risk factors are associated with cataracts:

• One of the major factors is increasing age, which is often responsible for nuclear and cortical opacities.
• Ethnic variation can be associated with different types of cataracts and variable rates of prevalence.
• Genetic factors are held responsible for nearly half of the severity of nuclear cataracts and are considered important in development of cortical cataracts. The studies show that recessive genes are potential inciters of cortical and nuclear cataract development.
• According to the evidence, women have a greater chance of developing cataracts than men.
• External factors responsible for Cataractogenesis (development of cataracts) are sunlight, cigarette smoking, alcohol consumption, lack of nutritional supplements, and lower education. Further, the studies reveal that artificial light sources such as ultraviolet B (UV-B) rays produce lens opacities in the human eye leading to cortical cataract development. These factors are also related with certain health problems.
• Common medical factors such as diarrhea, dehydration, diabetes, obesity, hypertension, use of steroids, and use of certain systemic medications, increases the risk of cataracts. Diabetes appears to be largely associated with development of cortical and posterior subcapsular cataracts, subjecte to the duration of the disease and degree of successful diabetes control. The studies have found that diabetics suffer a greater chance of cortical lens opacities or require cataract surgery than nondiabetics. Moreover, diabetes seems to be associated with early-age cataract development.
• Poor nutrition is also an indicator of higher cataract risk, especially deficiency of antioxidant vitamins A, C, and E are significant.

Diagnosis

The diagnosis of cataracts is done through estimation of visual function, which requires the measurement of visual acuity with the help of a vision chart. The vision chart consists of black letters on a white background, which the patient has to read in a darkened room from a distance and with lights on for near vision.

For proper detection of ocular diseases, like dry eyes or abnormal cornea, it is necessary to have an ophthalmic eye examination, as these could impede a successful cataract surgery. It would also help to avoid other causes diabetic retinopathy, macular degeneration, or glaucoma. The examinations include measurement of vision using a slit-lamp, testing intraocular pressure, and dilation of pupils for thorough examination of the lens, fundus, and vitreous inside the eye.

Treatment

Sophisticated surgical techniques have made removal of cataracts easier than ever. The use of viscoelastics, phacoemulsifcation and the development of intraocular lenses, have made treatment quite effective and ensures steady visual recovery in most cases.

Cataract surgery essentially depends on the visual needs. There are a few cases of ocular disease, such as diabetic retinopathy, that might not justify cataract surgery. The patient needs to be informed on other options such as use of low-vision aids, and of the effect of surgical intervention before a decision on whether or not to have surgery can be made.

TMethods of delaying or preventing cataract development have still to be discovered. Currently there are no proven ways to stop cataracts from developing other than maintaining a healthy lifestyle and cutting out the apparent risk factors such as smoking and nutrient deficient diets.

Cataract surgeries have a high rate of success, but no procedure is without risk. So, before deciding on cataract surgery, the risks, benefits, and patient’s expectations should be evaluated by the doctor. The patient too must decide whether the benefits of surgery outweigh the risks.