What exactly do you want to do in the opthalmology area?
Many opthalmologists just 'treat patients'. For eg, a patient is referred to them by a GP as having an eye problem, the opthalmologist then diagnoses the problem and treats it with medication or if it just concerns minor surgery the opthalmologist might perform the minor surgery, or if it's a major problem, the opthalmologist might then refer the patient to another specialist, like an eye/nose/throat surgeon who has specified skill in that kind of surgery.
What a scientist with a background in vision/biomedical science does is he/she actively finds new medications, or new ways of treatment, new diagnostic technique etc, all of which the opthalmologists then use when they're treating patients. So vision/biomedical scientists are often the pioneers in research. Because of their medical background, opthalmologists can also do this kind of research. I don't have the statistics in front of me but I think most opthalmologists focus predominantly on the treating patients.