Typical open angle and angle closure glaucoma are called primary glaucoma, since they are diseases in and of themselves and not caused by any other factors. Glaucoma can also be a result of other eye conditions or general body diseases. This is referred to as secondary glaucoma because it is caused by “something else” (see section on Secondary glaucoma). In secondary glaucoma, the damage always comes from having an eye pressure higher than the normal range. The reason for the abnormally high pressure is some obstruction to outflow of aqueous humor through the trabecular meshwork.

One of the most common kinds of secondary glaucoma happens when new blood vessels grow in the eye and block aqueous outflow (neovascular glaucoma). This can happen in people who have had diabetes mellitus or another disease of the blood vessels in the body for some years. It also happens when blood flow to the eye is disturbed by obstruction of the main vein that drains the retina inside the eye (central vein occlusion) or by obstruction in the large arteries that connect the heart to the brain and eye (carotid artery occlusion). There are specific diagnostic tests for blood flow in the eye called fluorescein angiography and also there are non-invasive tests for flow in the carotid arteries, which are the great vessels that course along our neck, using ultrasound machines. In cases of neovascular glaucoma related to diabetes and central vein occlusion, specific laser treatment of the retina is performed to eliminate these new blood vessels (pan-retinal photocoagulation). In acute situations, we can also do injections of anti-blood vessel medicines (blockers of vascular endothelial growth factor) into the eye. This is done under local anesthesia in the office.

Another common form of secondary glaucoma occurs when corticosteroid drugs are taken, leading to higher than normal eye pressure. There are many different chemical names for “steroids” of this type, with the most common name being prednisone or cortisone. These agents are given as pills, nasal sprays, inhalers, and even into the eye for some conditions. With a high enough dose, steroids can cause eye pressure increase in nearly everyone. So, it is more a matter of degree of risk than an all or none response. While there is a “glaucoma caution” on the Food and Drug Administration paperwork for all such drugs, non-eye doctors who treat you need to know that you have glaucoma. Among the common disorders for which steroids are given are asthma and arthritis—but the steroid can be mixed in with other drugs in combination and the name may not be a good clue. Always check with your eye doctor if you have been suggested to use or to receive a medication containing steroid.

When eye pressure rises due to corticosteroids, it can be lowered by typical glaucoma medications or even surgery. Stopping the steroid will also help to normalize the eye pressure in many, but not all cases. Naturally, those who already have glaucoma are at more risk from such an increase in pressure than are those with no existing glaucoma. Patients who are given “eye drops” from non-eye physicians may not be aware that these are often combinations of antibiotics and corticosteroids, and that the regular use of such eye drops can over an extended period lead to vision loss.

Those who undergo eye surgery for conditions other than glaucoma can have an eye pressure that becomes and stays high; this is considered glaucoma secondary to surgery. The operation to treat cataract is generally successful and uncomplicated, but a small number of patients will have complications including high eye pressure. Or, secondary glaucoma can be a result of another major eye disease that leads to blocking of aqueous humor outflow. Since eye pressure is nearly always measured by eye doctors who are taking care of these eyes, the situation rarely goes unnoticed. Medical and surgical glaucoma treatment may need to be added to the already performed procedures.

Severe injuries to the eye can cause traumatic glaucoma, due either to damage to the trabecular meshwork by the blow or rupture of the eye wall, or by blood in the eye and other obstructive material blocking the outflow of aqueous. Many of these secondary, injury-related glaucoma situations are temporary and quiet down without need for long-term treatment. Some, however, become threats to vision and require long-term treatment.

Various conditions cause inflammation in the eye and increase eye pressure (inflammatory glaucoma). In each part of our body, defense mechanisms ward off invading bacteria and viruses or respond to injury in their own way. When we get a cold or flu, our nose runs, we cough, and the skin can get red and itchy from blood vessel reactions. These are all-natural ways our body fights off the infection and returns us to health, but they feel unpleasant while they happen. Inflammatory diseases happen when the normal defense reactions get activated incorrectly, and actually cause disease by themselves. In the eye, this happens with forms of arthritis, with cancers like lymphoma, HIV-AIDS, and sometimes for no known reason (in this case the disease is called “idiopathic”). Inflammation blocks up outflow of aqueous and so causes secondary glaucoma. Anti-inflammatory medicines include corticosteroids, which as mentioned can raise the pressure further if the inflammation isn’t stopped promptly.