Cataracts are cloudy or misty patches that occur in the lens of the eye and blur vision. Cataracts are the most common cause of poor vision and can even cause blindness in severe cases. The most common form of the condition is age-related. Sometimes, cataracts are secondary symptoms that manifest as a result of other conditions.
Cataracts can be categorized according to where they form, as follows:
- Anterior cortical cataract
- Posterior cortical cataract
- Anterior polar cataract
- Posterior polar cataract
- Anterior subcapsular cataract
- Posterior subcapsular cataract
Cataracts can also be described according the their cause and examples include:
Age-related cataracts – Age-related cataracts are further classified as cortical senile cataract, immature senile cataract (lens is partially opaque), mature senile cataract (completely opaque lens) and hypermature senile cataract (with liquefied lens).
Secondary cataracts – These are caused by other eye conditions such as uveitis or glaucoma or by illnesses such as diabetes.
Drug-induced cataract – The long-term intake of corticosteroid medication or the cholesterol-lowering agent ezetimibe can cause cataracts.
Traumatic cataract – These cataracts develops after physical trauma or injury to the eye. They may develop years after the injury.
Congenital cataract – Some congenital diseases cause cataracts to develop and examples include Alport's syndrome, Cri-du-chat syndrome, Patau's syndrome, Trisomy 18 (Edward's syndrome), Turner's syndrome and galactosemia.
Radiation cataract – Overexposure to infrared radiation (e.g. glass blowers), ionizing radiation (X-rays) or ultraviolet radiation (sun exposure) can cause cataracts to develop.