How long has the field of ophthalmology existed?
I would argue that the field of ophthalmology has existed for thousands of years. Successful cataract surgery has been described in many ancient medical texts (Romans, Greeks, Indians) by the use of a sharp needle or thorn to push away the clouded lens out of the field of vision. Even the code of laws by Hammurabi mentions eye surgery and its compensation/punishment for a successful/unsuccessful result.