An ophthalmologist is expert in the diseases, functions and anatomy of the eye. Ophthamologists may provide routine care such as vision testing and prescribe and fit eyeglasses or contact lenses, but ophthalmologists are also surgeons. They repair traumatic injuries to the eye and perform cataract and corneal surgery. Some of the indications that an ophthalmologists expertise is needed include distorted vision, floaters or flashes of light, double vision, loss of vision or bulging of one or both eyes. Patients with chronic diseases such as diabetes and high blood pressure should see an ophthalmologist regularly to prevent eye damage from complications such as diabetic retinopathy.