1. Definition
Cataract is defined as a clouding of the normally clear lenses in the eye. In healthy people, the lenses focus light onto the retina, allowing them to see clearly. For people with cataracts, as less light can travel through the lenses, their vision is affected and it will be similar to looking through a foggy glass. Clouded vision can affect all aspect of daily lives such as driving, reading or simply holding a conversation.
Most cataracts develop slowly and don’t disturb your eyesight early on. But with time, cataracts will eventually interfere with your vision. At first, stronger lighting and eyeglasses can help you deal with cataracts. However, if quality of life is continued to be impacted, a surgery should be considered.
Cataracts can be categorized bases on the location in which it occurs, or by its causes.
Base on the anatomic of the eyes:
– Nuclear cataracts: clouding happens only in the nucleus. As the cataract slowly progresses, the lens may even turn brown. Advanced yellowing or browning of the lens can lead to difficulty distinguishing between shades of color.
– Cortical cataracts: clouding occurs in the lens cortex only. As it slowly progresses, the streaks extend to the center and interfere with light passing through the center of the lens. People with cortical cataracts often experience problems with glare.
– Subscapsular cataracts: clouding occurs primarily in the capsule of the lenses. A subcapsular cataract often interferes with your reading vision, reduces your vision in bright light, and causes glare or halos around lights at night.
By causes:
– Senile cataracts: cataracts caused by aging.
– Secondary cataract. Cataracts can form after surgery for other eye problems, such as glaucoma. Cataracts also can develop in people who have other health problems, such as diabetes. Cataracts are sometimes linked to steroid use.
– Traumatic cataract. Cataracts can develop after an eye injury, sometimes years later.
– Congenital cataract. Some babies are born with cataracts or develop them in childhood, often in both eyes. These cataracts may be so small that they do not affect vision. If they do, the lenses may need to be removed.
– Radiation cataract. Cataracts can develop after exposure to some types of radiation.
2. Epidemiology
Cataract is the leading cause of blindness in the world. It is estimated that there are 30 million blind people in the world, 50 of whom are caused by cataracts. Cataracts show an increasing likelihood of developing with increased age. Approximately 85% of cases are classified as senile or mature cataracts.
In the UK alone, age-related cataracts are thought to affect around half of those aged over 65 years to some degree, with this figure rising to 70% in those aged over 85. In France, about 20% of individuals aged more than 65 years are affected, with this figure rising to 60% in those older than 85. Australian studies have shown that the prevalence of cataract doubles with each decade of age after 40 years and that nearly everyone aged 90 years or older is affected by cataracts. Other developed countries show similar incidence and prevalence of cataract.
3. Causes and risk factors
The main cause of cataracts is due to old age. Other causes of cataracts could include:
– Injury
– Radiotherapy treatment
– Smoking
– Diabetes
– UV light
– Steroid uses
Sources:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2396082/
http://www.mayoclinic.org/diseases-conditions/cataracts/basics/causes/con-20015113