Unless there's need for specialized medical or surgical treatment, getting eye exams and eyeglass prescriptions from an ophthalmologist as opposed to a optometrist is like getting your teeth cleaned by an oral surgeon rather than a dentist. Astigmatism and/or myopia, refractive errors, corneal disease, amblyopia? Optometrist. Ptosis, proptosis, endophthalmitis, macular degeneration, excess tearing, detached retina or trauma? Ophthalmologist.
To be fair, I had a dentist who was technically an oral surgeon but would sometimes even bump the hygienist and do the cleanings himself; because they were easy and he was bored. Same cost to me so I didn't mind.