In most cases, glaucoma develops without warning. For that reason, glaucoma has been called “the silent thief of sight”. In general, glaucoma can be divided into two main groups: closed angle and open angle. Closed angle glaucoma can appear suddenly and is often painful. Vision loss can progress quickly but the discomfort often leads patients to seek medical care before significant damage occurs. The more common open angle glaucoma develops without pain or warning and tends to progress at a slower rate. Patients are therefore often unaware of losing their vision until the disease has progressed. By the time these patients seek medical care, their vision is permanently lost.