As you describe it, NO. The voluntary part does not matter, the doctor gave them the drops anyway. As long as there is no lost time, after the day of the injury, no restricted duty you are ok. As long as the doctor gave the prescription medication at the office and did not give the employee any extra for home or a prescription, then not recordable.
Remember to investigate what got in the eye, how it got in there and what to do so it does not happen again.
Good Luck
Safety Management '82
Indiana State Univ.