Cataract surgery

Cataract surgery did not emerge from a desire to improve vision. It emerged from the recognition that a specific anatomical structure—the crystalline lens—could be physically displaced to restore sight, and that this displacement, if performed correctly, would not kill the patient.

The procedure known as couching is the earliest documented form of cataract surgery. The technique involves inserting a sharp instrument into the eye and pushing the clouded lens downward and backward, out of the visual axis. The lens, no longer blocking light, allows images to form on the retina. The patient becomes severely farsighted—unable to focus without thick corrective lenses—but can see shapes, colors, and movement where before there was only progressive darkness.

The most detailed ancient description appears in the Sushruta Samhita, an Indian medical text attributed to the physician Sushruta, who practiced at the University of Benares (Varanasi) on the banks of the Ganges, likely between 800 and 600 BCE. The Uttaratantra section of this work devotes eighteen chapters to ocular diseases, describing seventy-six different conditions of which fifty-one require surgical intervention. For cataracts, Sushruta prescribed a curved needle to push the opaque 'phlegmatic matter' out of the visual pathway, followed by irrigation with warm clarified butter and bandaging.

The adjacent possible for cataract surgery required extraordinary courage and anatomical knowledge. The surgeon needed to understand that the eye contained a discrete structure—the lens—that could be displaced without destroying the organ entirely. They needed instruments sharp and fine enough to penetrate the tough outer coat of the eye without excessive trauma. They needed the nerve to push a needle into a living patient's eye, knowing that failure meant permanent blindness or death from infection.

Sushruta's text emphasizes surgical ambidexterity—the ability to operate with either hand—suggesting that precision and control were paramount. The procedure demanded practice, likely on animal eyes and cadavers before attempting human patients. The Golden Age of Surgery in ancient India rested largely on Sushruta's accomplishments and his systematization of surgical training.

The question of where cataract surgery originated remains contested among historians. While Indian sources provide the most detailed early descriptions, hints in medieval Arabic writings and ambiguous archaeological evidence suggest that cataract aspiration—a different technique extracting soft cataracts through suction—may have been practiced in Greco-Roman antiquity. The emphasis on ambidexterity in the Sushruta Samhita has led some scholars to suggest Mediterranean influences. Ophthalmic historian Julius Hirschberg concluded that whether Indians actually invented the procedure can neither be confirmed nor denied.

What is certain is that knowledge of couching spread along the Silk Road. The procedure was introduced to China from India during the late Western Han Dynasty (206 BCE to 9 CE). Arab physicians learned the technique and transmitted it to Europe during the medieval period. By the time of the Renaissance, couching was practiced throughout the Old World—a technology that had traveled from Varanasi to Venice within roughly two thousand years.

Couching remained the dominant form of cataract surgery until the eighteenth century. In 1752, Jacques Daviel of Paris presented his extraction technique—actually removing the lens from the eye rather than merely displacing it—beginning the gradual obsolescence of the ancient method. Modern phacoemulsification, which uses ultrasound to break up the lens for easier removal, descends from Daviel rather than Sushruta.

By 2026, cataract surgery is among the most commonly performed procedures worldwide, with approximately twenty million operations annually. The conditions that made it inevitable—the universal human experience of lens clouding with age, the devastating social consequences of blindness, the anatomical accessibility of the eye—persist wherever populations grow old.