By definition, specialists are doctors who have studied a specific area of expertise in their medical training, and who have completed residency in that specialty. Board-certified physicians have additional, rigorous training, and commit to continuing education to stay on the cutting edge of techniques and knowledge in their field of practice.
In general, specialists are those physicians not considered primary care practitioners. A few examples of medical specialties are: cardiology (heart), podiatry (feet), gastroenterology (digestive system), rheumatology (muscles and joints), and dermatology (skin). It must be noted, however, that there are exceptions to that definition. Some specialists-such as pediatricians, internists, and gynecologists-do provide primary care.
To muddy the waters even more, modern medicine has another level of expertise referred to as sub-specialties. Physicians in sub-specialties have additional training with more in-depth specifics of their field of knowledge. For example, a doctor in pediatrics may further specialize in neonatal cardiology, or a psychiatrist may focus on drug addictions.
When the ophthalmologist visit failed to produce answers, I was sent to a sub-specialist-a neuro-ophthalmologist. Before that visit, I never knew that such expertise existed. Because of the depth of his focused area of expertise, he was able to pinpoint the cause of my problem.