Patients are often referred to medical specialists by their family doctor, a general practitioner, or clinic. This procedure is intended, in part, to screen the patient through general examinations to get an overview of his or her health and detect related or unrelated health problems that the specialist may or may not be concerned with or qualified to treat. Therefore the availability of special medical services which do not require a preliminary general health screening may represent a hazard to public health. One example is the public's recourse to opticians and ophthalmologists for correction of eye problems that may by caused by disease. Another example is dental practice which establishes no relationship to the patient's medical history, sometimes with serious consequences. The public has direct access to psychologists and some psychiatrists for personality disorders, but medical screening might show a physiological cause and offer appropriate treatment. Other therapies for which general practitioner referral is not required are physical therapy, massage, chiropracty, acupuncture, hearing aids, some prosthetic services, and nutritional and diet regimes. Holistic medical services for the public are obstructed by tradition and economic considerations, as most holistic methodologies are not covered by insurance policies.