Also sometimes referred to as intensivists, critical care specialists are physicians with specialized training in the diagnosis and management of life-threatening conditions. Some of these conditions affect vital organs like the heart and lungs, those that make breathing difficult or impossible, and those that affect entire organ systems, like the renal system.
Critical care specialists are typically found in a hospital's intensive care unit where they monitor patients with life-threatening conditions and make determinations as to the best course of treatment.

Anesthesiologists are physicians who are trained to administer anesthetics, which are medicines used to block nerve sensation. Anesthesia can be either local to one specific part of a body, like a tooth, or regional to block feeling to a larger portion of the body, such as during an epidural for child birth. It can also be more general to block sensation to the entire body, resulting in unconsciousness.
Anesthesiologists assist in surgery by determining how much anesthesia is necessary and by monitoring the patient's level of responsiveness and vital signs throughout the procedure. The anesthesia specialist will also bring the patient out of anesthesia and then continue to monitor his or her vital signs post-operation.
Besides assisting in surgeries, anesthesiologists may also treat patients suffering from chronic pain.

An ophthalmologist has the training to do much more than just prescribe glasses. They are physicians specially trained to diagnose and treat disorders of the eyes and vision. These doctors are experts on the complicated anatomy of the eye and are trained to treat eye diseases through both medical and surgical methods.
Some common conditions that ophthalmologists treat are cataracts, glaucoma, strabismus, diabetic retinopathy, macular degeneration and amblyopia. In addition, ophthalmologists can provide prescriptions for eye glasses and contact lenses and perform LASIK surgery and other corrective surgeries for refractive errors like myopia (near-sightedness), hyperopia (far-sightedness), astigmatism and presbyopia.