Lifestyle can differ between the two professions. Like the above posters said, shadow them and ask the doctors questions about what their life is like, their daily routines, if they are happy doing what they are doing, what they like and don't like about it.
Optometry can be more of a 9 to 5 job whereas ophthalmology, it is harder to get that. Ophthalmology also requires a lot more schooling and it is EXTREMELY competitive to get accepted into it after Medical school. You have to be really smart! Ask yourself if you do medical school and don't get accepted into ophthalmology, will you be happy doing something else in the medical field or is that the only thing you want? You should have a backup plan if you decide to go that route.