The word cataract comes from the Greek for waterfall. Until the mid 1700s, it was thought that a cataract was formed by opaque material flowing, like a waterfall, into the eye. People with cataracts have blurred vision, making everyday activities such as driving and reading difficult.
Successful cataract surgery restores the ability to perform these activities.
The earliest written reference to cataract surgery is found in Sanskrit manuscripts dating from the 5th century BC. They are said to be written by the Hindu surgeon Susruta. He practiced a type of cataract surgery known as couching, in which the cataractous lens was displaced away from the pupil to lie in the vitreous cavity in the back of the eye.
This displacement of the lens enabled the patient to see much better. Vision, however, was still blurred because of the unavailability of corrective lenses. As recently as the middle of this century, couching was still practiced in Egypt, India, and Tibet.
In the Western world, recent excavations in Babylonia (Iraq), Greece, and Egypt have uncovered bronze instruments that would have been appropriate for cataract surgery.
The first written description of the cataract and its treatment in the West appears in 29 AD in De Medicinae, the work of the Latin encyclopedist Celsus. He describes in this work the practice of needling of cataracts, a technique in which the cataract is broken up into smaller particles, thereby facilitating their absorption.
Interestingly, Hippocrates does not refer to cataract surgery in his writings. Galen, the pivotal medical figure of antiquity whose theories went unchallenged for more than 1,500 years, erroneously believed that the lens rather than the retina was the seat of vision, and that its removal would cause blindness.
For the relevant passage(s) from Celsus, see David Noy's materials for his Ancient Medicine course (not quite half way down)