Cataract Surgery
Cataracts have always been a problem for those who are getting older or face problems with their eyes. The 5th century BC is the first documented appearance of a type of cataract surgery. When the cataract had become so advanced that the entire lens was opaque, rigid, and heavy, the eye would be struck with a blunt object. This would cause the zonules which had been weakened due to the cataracts to break, causing the lens to dislocate. This would lead to slightly restored vision, but vision that was perpetually unfocused.
In medieval times the process somewhat improved by the standards of physicians of the time. The medieval procedure involved inserting a sharp object, such as a knife or large needle, through the cornea. Once inserted the sharp object would be used to force the lens out of its capsule. Once the lens was out of its capsule it would be pushed down to the bottom of the eye.
While this was sometimes successful in getting some very limited vision back to the patient it typically did little to improve the vision of the patient all while being rather uncomfortable. This process continued until Islamic medicine began to spread to medieval Europe. Then it was realized that a syringe could be used to extract cataracts by using the suction of the syringe.
From then on the process involved putting a hypodermic syringe into the white part of the eye and then removing the cataract through pulling back on the syringe and sucking it up. This process was successful at removing cataracts and more likely to actually improve the sight of the patient than the medieval methods.