Sign and symptoms:

Signs and symptoms vary depending on the type of cataract, though considerable overlap occurs. People with nuclear sclerotic or brunescent cataracts often notice a reduction of vision. Nuclear cataracts typically cause greater impairment of distance vision than of near vision. Those with posterior subcapsular cataracts usually complain of glare as their major symptom.

The severity of cataract formation, assuming no other eye disease is present, is judged primarily by a visual acuity test. Other symptoms include frequent changes of glasses and colored halos due to hydration of lens.

Causes

Age
Radiation 
Trauma
Genetics
Skin disease 
Smoking and alcohol
Medications

Post-operative

Nearly every person who undergoes a vitrectomy—without ever having had cataract surgery—will experience progression of nuclear sclerosis after the operation.This may be because the native vitreous humor is different from the solutions used to replace the vitreous (vitreous substitutes), such as BSS Plus.This may also be because the native vitreous humour contains ascorbic acid which helps neutralize oxidative damage to the lens and because conventional vitreous substitutes do not contain ascorbic acid.Accordingly, for phakic patients requiring a vitrectomy it is becoming increasingly common for ophthalmologists to offer the vitrectomy combined with prophylactic cataract surgery to prevent cataract formation

The appropriateness of surgery depends on a person's particular functional and visual needs and other risk factors.Cataract removal can be performed at any stage and no longer requires ripening of the lens.[clarification needed] Surgery is usually "outpatient" and usually performed using local anesthesia. About 9 of 10 patients can achieve a corrected vision of 20/40 or better after surgery.

Several recent evaluations found that cataract surgery can meet expectations only when significant functional impairment due to cataracts exists before surgery. Visual function estimates such as VF-14 have been found to give more realistic estimates than visual acuity testing alone.In some developed countries, a trend to overuse cataract surgery has been noted, which may lead to disappointing results.

Phacoemulsification is the most widely used cataract surgery in the developed world.This procedure uses ultrasonic energy to emulsify the cataract lens. Phacoemulsification typically comprises six steps:

Anaesthetic – The eye is numbed with either a subtenon injection around the eye (see: retrobulbar block) or topical anesthetic eye drops. The former also provides paralysis of the eye muscles.
Corneal incision – Two cuts are made at the margin of the clear cornea to allow insertion of instruments into the eye.
Capsulorhexis – A needle or small pair of forceps is used to create a circular hole in the capsule in which the lens sits.
Phacoemulsification – A handheld ultrasonic probe is used to break up and emulsify the lens into liquid using the energy of ultrasound waves. The resulting 'emulsion' is sucked away.
Irrigation and aspiration – The cortex, which is the soft outer layer of the cataract, is aspirated or sucked away. Fluid removed is continually replaced with a saline solution to prevent collapse of the structure of the anterior chamber (the front part of the eye).
Lens insertion – A plastic, foldable lens is inserted into the capsular bag that formerly contained the natural lens. Some surgeons also inject an antibiotic into the eye to reduce the risk of infection. The final step is to inject salt water into the corneal wounds to cause the area to swell and seal the incision.
A Cochrane review found little to no difference in visual acuity as a function of the size of incisions made for phacoemulsification in the range from ≤ 1.5 mm to 3.0 mm.Extracapsular cataract extraction (ECCE) consists of removing the lens manually, but leaving the majority of the capsule intact.] The lens is expressed through a 10- to 12-mm incision which is closed with sutures at the end of surgery. ECCE is less frequently performed than phacoemulsification, but can be useful when dealing with very hard cataracts or other situations where emulsification is problematic. Manual small incision cataract surgery (MSICS) has evolved from ECCE. In MSICS, the lens is removed through a self-sealing scleral tunnel wound in the sclera which, ideally, is watertight and does not require suturing. Although "small", the incision is still markedly larger than the portal in phacoemulsification. This surgery is increasingly popular in the developing world where access to phacoemulsification is still limited.

Intracapsular cataract extraction (ICCE) is rarely performed The lens and surrounding capsule are removed in one piece through a large incision while pressure is applied to the vitreous membrane.The surgery has a high rate of complications.