It involved physically shoving the cataract-covered lens back into the eyeball in an attempt to allow a little more light to enter. (Bach would die from septicemia induced as a consequence of contaminated instruments). As this surgery was done without anesthesia, the courage and physical constitution of both men must have been amazing!
I hate when I hear about things like this. I know it was the way at the time, but what a shame. Gives me the creeps!