According to WHO, eye care is one of the greatest public health challenges for the 21st century. About 285 million people are visually impaired worldwide: 39 million are blind and 246 million have low vision. Cataract causes nearly third cases of visual impairment and more than half cases of blindness. The number of people blind from cataract in the world is increasing by approximately 1 million per year. Most of these people live in the developing world, where poor nutrition and limited access to eye care can mean a life limited by needless blindness.

Incidence rates of cataracts is expected to continue rising predominantly in developing countries where population growth is the greatest, with increasing in the people age 65 or over. Even the disease is more prevalent in older adults, Cataract is also the most important cause of treatable childhood blindness, as per International Centre for Eye Health, UK. Women bear approximately two-thirds of the global burden of blindness, with cataract being the major cause of it.

A cataract is a cloudy area in the normally clear lens of the eye which can interfere with normal vision. Usually, cataracts develop in both eyes, but one may be worse than the other. As cataract progresses, the person starts facing visual problems, such as blurred vision and sensitivity to glare. Symptoms worsen with time to affect daily tasks.

Most cases of cataract are age-related. They appear first in 40s or 50s, but may not affect vision until after age 60. In other cases, cataracts may be related to eye trauma, diabetes, smoking, corticosteroid medications or ultraviolet radiation. Sometimes it may be congenital.

The symptoms of early cataract may be improved with new eyeglasses, brighter lighting, anti-glare sunglasses, or magnifying lenses. If these measures do not help, surgery is the only effective treatment. Cataract surgery is very helpful to correct vision impairment. It aims at replacing diseased lens with another synthetic, healthy one.

Cataract is the leading cause of blindness globally. As the world's population ages, visual impairment due to cataract is on the increase. Low vision is another common complication of cataract that makes everyday tasks difficult. These problems can be efficiently treated to omit an unnecessary suffering.

Several ways are available to reduce the chance of having cataracts. Protecting eye from ultra-violent waves and give up smoking are in this context. People with diabetes benefit from controlling their blood sugar. Taking missed Rubella vaccine before pregnancy and following up throw it will help prevent infection-related congenital cataracts.

Cataract is a clouding of the eye's lens. The lens is a transparent part located inside the eye behind the iris, the colored part of the eye. Normally, the lens focuses light rays on the retina to create an image and send it through the optic nerve to the brain. The lens also adjusts the eye’s focus, letting us see things. Changes in the lens of the eye cause it to become less clearly, so the light is scattered hence the lens can no longer focus it properly, causing misty vision. A cataract can occur in either or both eyes. It cannot spread from one eye to the other.

The lens is composed of 3 layers. A cataract may develop in any of them and is named for its location in the lens:

• A nuclear cataract: Located in the center of the lens, which limit vision more severely than cataracts in other sites. The nucleus tends to darken, changing from clear to yellow and sometimes brown;
• A cortical cataract: Affects the layer of the lens surrounding the nucleus that is called the cortex. The cataract looks like a wedge or a spoke;
• A posterior capsular cataract: found in the back outer layer that enclose the lens. This type often develops more rapidly and more frequent in people with diabetes and overweight.

Cataracts are the result of changes in the structure of the lens, mainly with aging. The lens is made of mostly water and protein. The protein is arranged in a precise way that keeps the lens clear and lets light pass through it. But as we age, some of the protein may clump together and start to cloud a small area of the lens. Over time, the problem may grow larger and cloud more of the lens, making it harder to see. Cataracts can also be caused by other eye conditions, past eye surgery, or medical conditions, such as diabetes.

• Aging. Most cataracts are related to aging, thus cataract is very common in older people. It is after age 60 that age-related cataracts are most likely to affect vision, though the condition starts usually in 40s or 50s;
• Exposure to ultraviolet (UV) sunlight. UV light can damage lens proteins by triggering harmful oxidative reactions in the lens;
• Smoking. Smoking a pack a day of cigarettes doubles the risk of developing cataracts, particularly nuclear cataract. The risk continues to increase with more smoking;
• Prolonged use of certain drugs. These include: Corticosteroids, Glaucoma medications, Psoralens (for psoriasis), and antipsychotic drugs, such as Chlorpromazine;
• Nutritional deficiency. Low levels of antioxidants, such as vitamin C, vitamin E and carotenoids, may deprive eyes from their protective role;
• Prenatal factors. Congenial cataract may occur as a result of an infection that happened during pregnancy, especially toxoplasmosis, cytomegalovirus, syphilis, rubella or herpes simplex;
• Certain diseases. People with diabetes are much more likely to develop cataract at a younger age. Hypertension may also increase cataract risk of cataract;
• Previous eye injury. Cataracts can develop after an eye trauma, such as a hard blow, cut, or puncture. Sometimes the problem can appear years later;
• History of eye surgery. Cataracts can form after surgery for other eye problems, like glaucoma;
• Other Eye Conditions, such as glaucoma, Myopia (nearsightedness), Uveitis (chronic eye inflammation);
• Hereditary factors. Cataracts may be associated with a subgroup of genes encoding proteins important to maintain the lens transparency and homeostasis;
• Gender. Women face a higher risk than men to have cataract. They are also more prone to have blindness as cataract complications;
• Race. African-Americans have nearly twice the risk of developing cataracts as Caucasians. Hispanics are also at increased risk;
• Excess weight. Obesity has been proposed to be a risk factor for cataract development, though the exact underlying mechanisms are unclear;
• Excessive alcohol Drinking. Chronic heavy drinkers are at high risk for a number of eye disorders, including cataracts;
• Environmental Factors. Long-term lead exposure may increase the risk of developing cataracts. This is also True for gold and copper;
• Exposure to radiation. Prolonged exposure to ionizing radiation (such as x-rays, gamma rays) can increase cataract risk.

The pathogenesis of cataract is multifactorial involving complex interactions between various physiologic processes modulated by environmental, genetic, nutritional, and systemic factors. As the lens ages, its composition changes while its accommodative power decreases. The main mechanisms of cataract are:

• Progressive oxidative damage to the lens that takes place with aging. an increase in products of oxidation, and a decrease in antioxidant vitamins and the enzyme superoxide dismutase;
• Changes of lens protein solubility and molecular weight cause abrupt fluctuations in the refractive index of the lens, scatter light rays, and reduce transparency;
• A decrease in lens epithelial cell density and an aberrant differentiation of lens fiber cells. The accumulation of small scale epithelial losses progresses and ultimately leads to loss of lens transparency;
• A reduction in the rate at which water can enter the cells of the lens nucleus via the epithelium and cortex occurs with a subsequent decrease in the rate of transport of water, nutrients, and antioxidants in the eye.

• Cloudy, blurry, or foggy vision;
• Reduced intensity of colors to seem faded;
• Increased sensitivity to glare from light sources like car and sun lights;
• Poor night vision;
• Double vision, or multiple images in one eye;
• Frequent prescription changes in eyeglasses or contact lenses;
• Progressive nearsightedness in older people;
• Difficulty in reading due to reduced black-white contrast.

To check for cataract, the doctor will review medical history and symptoms, then he will perform a comprehensive eye examination. The doctor may conduct several tests, including:

• Visual acuity test. The doctor uses an eye chart to measure how well the person can see a series of letters. The eyes are tested one at a time, while the other is covered. The doctor can determine if the person has 20/20 vision or if there are signs of impairment;
• Slit-lamp examination. A microscope uses an intense line of light called a slit to illuminate the cornea, iris, lens, and the space between iris and cornea. The slit allows the doctor to view these structures in small sections, which makes it easier to detect any tiny abnormalities;
• Dilated eye exam. Drops are placed in the eyes to widen, or dilate, the pupils. After that the eye care professional uses a special magnifying lens to examine the retina and optic nerve for signs of damage and other eye problems;
• Tonometry. An instrument measures the pressure inside the eye and mainly used to screen for glaucoma. For this test, an orange dye is applied to the eye, then a Blue light is used closely to it in order to investigate eye pressure by detecting changing of the dye color.

Cataract treatment is based on the level of visual impairment they cause. If a cataract minimally affects vision, or not at all, no treatment may be needed. Patients may be advised to monitor for increased visual symptoms and follow a regular check-up schedule.

• Coping mechanisms: In some cases, changing the eyeglass prescription may provide temporary vision improvement. In addition, anti-glare coatings on eyeglass lenses can help reduce glare for night driving, and increasing the amount of light used when reading may be beneficial. When a cataract progresses to the point that it affects a person's ability to do normal everyday tasks, surgery may be needed and considered the only working treatment for cataract.
• Cataract surgery: Cataract removal is one of the safest, most common and effective operations performed. In this procedure, the cloudy natural lens is removed and replaced with a clear artificial lens implant (called an intraocular lens, or IOL). Cataract surgery is generally done on an outpatient basis and lasts for a while. During the surgery, the doctor uses local anesthetic to numb the area around the eye, but the patient usually stays awake during the procedure. As with any surgery, cataract surgery poses risks, such as infection, bleeding and inflammation (pain, redness, and swelling). It slightly increases the risk of retinal detachment. After the procedure, the patient will have some discomfort for a few days. Healing generally occurs within eight weeks. If both eyes are affected, the second eye operation will be scheduled after the healing of the first one. After surgery, the eye must be kept clean, and hands should be washed before touching it. Some medications may be prescribed. Sometimes the eye tissue that encloses the implanted lens becomes cloudy and may blur vision. This condition is called an after-cataract and can develop months or years after cataract surgery. An after-cataract is treated with a laser. The doctor uses a laser to make a tiny hole in the eye tissue behind the lens to let light pass through. This outpatient procedure is called a YAG laser capsulotomy.

• Low vision. Cataract is the second principal cause of visual impairment in the world, forming nearly 33% of total cases (World health organization). Cataract is an important cause of low vision in both developed and developing countries. It can harden the ability to do regular activities and put the patient under the risk of falling down or having an accident;
• Blindness. Cataract can progress to cause in ability to see in the affected eye/eyes. World health organization (WHO) says that Cataract is responsible for 51% of world blindness. Lost vision may have a huge impact on the ability to work, interact and on the quality of life.

In general, there is currently no way to prevent age-related cataract; however, people can decrease their risk of developing cataracts by:

• Staying out of the sun, as the simplest and most effective way to protect against ultraviolet (UV) rays, with caring about vitamin D that needs sun exposure to be produced internally;
• Wearing sunglasses and a hat with a brim when get outside in sunny day to block ultraviolet sunlight from reaching the eye;
• Consuming eye healthy nutrients, such as lutein, zeaxanthin, vitamin C, vitamin E and zinc. They are found on green leafy vegetables, carrot, sweet potatoes, fruits, and eggs;
• Having a comprehensive dilated eye exam at least once every two years from age 60 and older;
• Managing other health problems that may cause cataract such as diabetes. This can be achieved by following a complete treatment plan;
• Quitting smoking and limiting alcohol. The person can favor from counseling and certain prescribed drugs that can help.

Cataract usually develops slowly over several years and are related to aging. In some cases, loss of vision progresses rapidly. Depending on how dense they are and where they are located, cataracts can block the passage of light through the lens and interfere with the formation of images on the retina, causing vision to become cloudy. Cataract progresses with time until the person becomes blind.

Although some measures may help to deal with the symptoms of low vision, cataract Surgery is the only type of treatment that's proven to be effective for cataracts. According to, National health institutes, USA, about 90 percent of people who have cataract surgery, have better vision afterward. In most cases, delaying cataract surgery will not cause long-term damage to the eye or make the surgery more difficult.

According to WHO, eye care is one of the greatest public health challenges for the 21st century. About 285 million people are visually impaired worldwide: 39 million are blind and 246 million have low vision. Cataract causes nearly third cases of visual impairment and more than half cases of blindness. The number of people blind from cataract in the world is increasing by approximately 1 million per year. Most of these people live in the developing world, where poor nutrition and limited access to eye care can mean a life limited by needless blindness.

Incidence rates of cataracts is expected to continue rising predominantly in developing countries where population growth is the greatest, with increasing in the people age 65 or over. Even the disease is more prevalent in older adults, Cataract is also the most important cause of treatable childhood blindness, as per International Centre for Eye Health, UK. Women bear approximately two-thirds of the global burden of blindness, with cataract being the major cause of it.