What Are the Most Common Types of Glaucoma?
Glaucoma is a broad term used to describe a number of different conditions, all of which can result in optic nerve damage. Most of these conditions involve elevation of the intraocular pressure, but not always. The most common types of glaucoma-related conditions include:
Ocular Hypertension (OHT): A condition where the intraocular pressure (IOP) is elevated but without any evidence of optic nerve damage or visual field loss. Patients with OHT will need regular monitoring for glaucoma, since IOP elevation is a major risk factor for glaucoma development.
Glaucoma Suspect: A situation where significant glaucoma risk factors are present, or where the findings of the clinical exam raise the suspicion of possible glaucoma (such as elevated IOP or questionable changes in the optic nerve). These patients require glaucoma surveillance exams at regular intervals.
Primary Open Angle Glaucoma (POAG): This is the most common type of glaucoma in the United States. POAG develops when the drainage system of the eye (the TRABECULAR MESHWORK) stops working properly. There is increased resistance to aqueous fluid drainage, resulting in a buildup of aqueous within the eye, which leads to a rise in intraocular pressure (IOP). The elevated IOP causes loss of optic nerve fibers. In POAG the pressure elevation may occur slowly over a long period of time. Typically there are no symptoms such as pain or blurred vision and the patient may thus be totally unaware that they have the condition. If the disease is undetected or untreated, however, optic nerve damage can occur with irreversible loss of vision. Most often when patients notice visual loss from POAG, the disease has likely reached an advanced stage, so it is very important to get checked early if you know you may be at risk.
Primary Angle Closure Glaucoma Suspect (Narrow Angle): A situation where the drainage angle of the eye is anatomically narrow, with crowding between the peripheral iris and the trabecular meshwork. A narrow angle increases the risk of angle closure glaucoma because the crowding in the angle makes it more likely that the iris will stick to the trabecular meshwork, forming adhesions and physically obstructing the drainage system. A narrow angle tends to worsen with time, especially as cataracts develop.
Primary Angle Closure Glaucoma: An anatomic closure of the drainage system that develops when the iris blocks the trabecular meshwork, generally in eyes that have narrow angles or crowding of structures within the eye. The closure can develop gradually over time with a rise in IOP without symptoms (chronic angle closure glaucoma), or suddenly (acute angle closure glaucoma) with symptoms that include pain, headache, nausea, vomiting, a red eye, and blurred vision. Acute angle closure glaucoma is a medical emergency which poses a permanent threat to the vision; it requires immediate attention to relieve the very high pressure that can develop.
Pigmentary Glaucoma: A condition where pigment is spontaneously released from the back surface of the iris. The pigment deposits in various structures inside the eye, including the fluid drainage system. Blockage of the trabecular meshwork by this pigment leads to IOP elevation. Pigmentary glaucoma tends to affect younger individuals, especially males.
Steroid-induced Glaucoma: Steroid medications that may be used to treat other conditions can cause a rise in IOP which can lead to optic nerve damage if not detected. The greatest risk would occur from topically administered steroid eye drops that are used to treat a number of ocular inflammatory problems, but IOP elevation can also develop from other types of steroid use, such as dermatologic cortisone-type preparations, prednisone or other oral steroid pills, or even injectable cortisone shots. Patients with an underlying predisposition towards glaucoma are more likely to develop IOP elevation or steroid-induced glaucoma. Patients taking steroid medications on a chronic or long-term basis need regular glaucoma monitoring examinations.
Neovascular Glaucoma: Glaucoma that develops due to the growth of abnormal blood vessels within the eye that block the trabecular meshwork and the drainage angle. These blood vessels most often form as a result of poor blood flow to the eye in conditions such as diabetic retinopathy, clots in the retinal circulation (vein occlusions), or blockages in the carotid artery. The treatment of neovascular glaucoma requires both the management of the elevated IOP and the underlying circulatory problem.
Normal Tension Glaucoma: In this type of glaucoma, there is evidence of optic nerve damage and/or visual field loss, despite IOP readings that consistently may be normal or even low. Factors other than intraocular pressure are likely at play, like poor blood flow to the optic nerve, or perhaps an excess of oxidative stresses that damage the optic nerve even without IOP elevation. Normal tension glaucoma patients may have an increased incidence of migraine headaches, Raynaud’s phenomenon, or low blood pressure, conditions that may be associated with impaired vascular stability or blood flow regulation. The treatment of normal tension glaucoma focuses on IOP reduction and on preventing very low blood pressure that may hinder proper blood flow to the optic nerve.
How Do You Protect Your Vision from Glaucoma?
Because the visual loss from glaucoma often occurs slowly over a long period of time, the patient may be totally unaware that there is a vision-threatening problem. Typically there is no pain or blurred vision. In fact, glaucoma is known as the “sneak thief of sight.”
For this reason, early detection and treatment by an ophthalmologist is the key to prevent your vision from being robbed.