How should this medicine be used? Ophthalmic gentamicin comes as a solution (liquid) to instill in the eyes and as an eye ointment to apply to the eyes. The eye drops are usually instilled every 4 to 8 hours and the eye ointment is usually applied two to four times a day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part that you do not understand.