When it comes to ophthalmic/eye care in America, surprisingly, most people are not well informed about the difference between different types of eye specialists, or which specialist to see for their particular eye problem.
For example, I had a recent patient ask why her previous 'eye doctor' had not recommended an operation for her glaucoma. I explained that although she called her Optometrist "Doctor", they are not actually physicians, and do not perform ophthalmic surgeries.
Optometrists (with "O.D." at the end of their name) complete 2-4 years of an undergraduate education, followed by 4 years of optometry school, which allows them to prescribe glasses for people with mostly healthy eyes (i.e., people that can be corrected to near perfect vision with only a pair of glasses).
Not to be confused with an Optometrist, an Ophthalmologist, or Ophthalmic surgeon, is a medical doctor. Ophthalmologists complete 4 years of undergraduate education, 4 more years of medical school, one year of general medical or surgical residency, another 3 years of ophthalmic-specific medical residency, and then an optional fellowship (to further sub-specialize within the field of ophthalmology) that can range usually from 1-2 years.
Since Ophthalmologists are also medical physicians (with "M.D." at the end of their name), they specialize in the medical and surgical treatment of people with ocular problems or disorders (i.e., people that may need ocular surgery or other medical treatments besides glasses to correct their vision).
Ophthalmologists also treat patients with medical or neurologic conditions that might secondarily involve their vision (common examples include diabetes, high blood pressure, or patients with brain tumors).
Therefore, if you do not have any significant medical problems, it is okay to have your vision checked first with an Optometrist, who can also screen for any other ocular abnormalities. If the Optometrist finds any ocular problem, or if your vision does not improve with glasses, it is best to see an Ophthalmologist at that point.
However, if you have any medical problems or sudden/acute vision changes, you should call an Ophthalmologist's office directly to request an appointment.
Depending on your insurance, sometimes a referral from your primary care doctor (PCP) is required, but most PCP's are happy to send the referral. An ophthalmology exam is also usually covered by your medical insurance, but it doesn't hurt to check with the Ophthalmologist's office first just in case.
To read more about what Ophthalmologists do, or to research where to find an Ophthalmologist, you can also visit the American Academy of Ophthalmology website, at AAO.org for more information.