Ophthalmology (/ˌɒfθælˈmɒlədʒi/, OFF-thal-MOL-ə-jee) is the branch of medicine that deals with the diagnosis, treatment, and surgery of eye diseases and disorders.

An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a medical degree, a doctor specialising in ophthalmology must pursue additional postgraduate residency training specific to that field. In the United States, following graduation from medical school, one must complete a four-year residency in ophthalmology to become an ophthalmologist. Following residency, additional specialty training (or fellowship) may be sought in a particular aspect of eye pathology.

Ophthalmologists prescribe medications to treat ailments, such as eye diseases, implement laser therapy, and perform surgery when needed. Ophthalmologists provide both primary and specialty eye care—medical and surgical. Most ophthalmologists participate in academic research on eye diseases at some point in their training and many include research as part of their career. Ophthalmology has always been at the forefront of medical research with a long history of advancement and innovation in eye care.

A former term for this medical branch is oculism.

A brief list of some of the most common diseases treated by ophthalmologists:

The most-valued pharmaceutical companies worldwide whose leading products are in ophthalmology are Regeneron (United States) for macular degeneration treatment and Bausch Health (Canada).

The following are examples of methods performed during an eye examination that enable diagnosis:^{[citation needed]}

Optical coherence tomography (OCT) is a medical technological platform used to assess ocular structures. Physicians then use the information to assess the staging of pathological processes and confirm clinical diagnoses. Subsequent OCT scans are used to assess the efficacy of managing diabetic retinopathy, age-related macular degeneration, and glaucoma.