There is a common misconception that cataracts represent opaque membranes growing in the eye when in reality they are the eye's natural lenses that become cloudy as we age. Cataract surgery is usually performed when this clouding effects our quality of life. The procedure involves using ultrasound or a combination of laser and ultrasound to dissolve the cataract. A lens implant is then inserted into the eye to replace the cloudy natural lens that was removed. 

The link below offers a great overview of the cataracts and modern cataract surgery.