Lasers are high powered lights that can be used to either cut or burn tissue.They have been used for more than thirty years in ophthalmology mostly for diabetes retina therapy, glaucoma, and after cataract membrane discission. Because they use light, they do not require an incision (hole) to cut or burn tissue inside the eye. This means there is less risk of infection or bleeding. Lasers also can be finely controlled by computers and thus allow more precision.
Modern cataract surgery is done by ultrsound and not laser. Cataract surgery involves not only removing an opaque cataract but also replacing it with an implant lens. Hence, the eyes must be opened to allow the placement of this lens. Laser devices are being developed to improve cataract surgery currently (2011) but they are not used by most ophthalmologists. Look for this in the near future.