Disorders of calcium and bone metabolism.

Calcium levels in blood are maintained within narrow limits by parathyroid hormone, acting on kidney, bone and gut. Our understanding of the mechanisms of these actions has increased greatly in recent years, for example by identification of new hormones (eg 1,25 dihydroxy vitamin D) and by the study of isolated bone cells. Though most clinical disorders of calcium metabolism are now readily diagnosed and many are effectively treated, some serious problems still remain. Foremost amongst these are the early diagnosis of osteoporosis and the treatment of osteoporosis after fractures have occurred. Most disorders of calcium metabolism have ophthalmologic manifestations, sometimes troublesome to the patient, and sometimes diagnostically helpful.