Other forms of glaucoma
Normal Tension Glaucoma
Also called low-tension or normal-pressure glaucoma, in normal-tension glaucoma the optic nerve is damaged even though the pressure in the eye is not very high. Doctors do not know why some people’s optic nerves are damaged even though they have almost normal pressure levels.
Those at higher risk for this form of glaucoma are:
- people with a family history of normal-tension glaucoma
- people of Japanese ancestry
- people with a history of systemic heart disease such as irregular heart rhythm.
How Normal-tension glaucoma is different
Glaucoma is a group of eye diseases that usually share common traits, such as high eye pressure, damage to the optic nerve and gradual sight loss. Most kinds of glaucoma involve elevated eye pressure.
Normal-tension glaucoma (NTG), also known as low tension or normal pressure glaucoma, is a form of glaucoma in which damage occurs to the optic nerve without eye pressure exceeding the normal range. In general, a "normal" pressure range is between 12-22 mm Hg.
What Causes Normal-tension Glaucoma?
The causes of NTG are still unknown. For some reason, the optic nerve is susceptible to damage from even the normal amount of eye pressure. Researchers continue to examine why some optic nerves are damaged by these relatively low eye pressure levels.
How Normal-tension Glaucoma is treated
Since so little is known about why normal eye pressure damages some eyes, most doctors treat normal tension glaucoma by reducing the eye pressure as low as possible using medications, laser treatments and conventional surgery.
Other types of glaucoma
Most other types of glaucoma are variations of open-angle or angle-closure types. These types can occur in one or both of your eyes.
Secondary glaucoma refers to any case in which another disease causes or contributes to increased eye pressure, resulting in optic nerve damage and vision loss.
Secondary glaucoma can occur as the result of an eye injury, inflammation, tumour, or in advanced cases of cataract or diabetes. It can also be caused by certain drugs such as steroids. This form of glaucoma may be mild or severe. The type of treatment will depend on whether it is open-angle or angle-closure glaucoma.
Pigmentary Glaucoma is a form of secondary open-angle glaucoma. It occurs when the pigment granules that are in the back of the iris (the coloured part of the eye) break into the clear fluid produced inside the eye. These tiny pigment granules flow toward the drainage canals in the eye and slowly clog them. This causes eye pressure to rise. Treatment usually includes medications, laser surgery, or conventional surgery.
This form of secondary open-angle glaucoma occurs when a flaky, dandruff-like material peels off the outer layer of the lens within the eye. The material collects in the angle between the cornea and iris and can clog the drainage system of the eye, causing eye pressure to rise. Pseudoexfoliative Glaucoma is common in those of Scandinavian descent. Treatment usually includes medications or surgery.
Injury to the eye may cause secondary open-angle glaucoma. Traumatic glaucoma can occur immediately after the injury or years later. It can be caused by blunt injuries that bruise the eye (called blunt trauma) or by injuries that penetrate the eye.
In addition, conditions such as severe near-sightedness, previous injury, infection, or prior surgery may make the eye more vulnerable to a serious eye injury.
The abnormal formation of new blood vessels on the iris and over the eye's drainage channels can cause a form of secondary open-angle glaucoma.
Neovascular glaucoma is always associated with other abnormalities, most often diabetes. It never occurs on its own. The new blood vessels block the eye's fluid from exiting through the trabecular meshwork (the eye's drainage canals), causing an increase in eye pressure. This type of glaucoma is very difficult to treat.
Irido Corneal Endothelial Syndrome (ICE)
This rare form of glaucoma usually appears in only one eye, rather than both. Cells on the back surface of the cornea spread over the eye's drainage tissue and across the surface of the iris, increasing eye pressure and damaging the optic nerve. These corneal cells also form adhesions that bind the iris to the cornea, further blocking the drainage channels.
Irido Corneal Endothelial Syndrome occurs more frequently in light-skinned females. Symptoms can include hazy vision upon awakening and the appearance of halos around lights. Treatment can include medications and filtering surgery. Laser therapy is not effective in these cases.
Congenital Glaucoma (Childhood Glaucoma)
Childhood Glaucoma refers to the presence of glaucoma in a child, and occurs in 1 out of every 10,000 births in the UK. Congenital glaucoma is the common term used for a glaucoma diagnosed in infancy or early childhood.
This glaucoma is caused by abnormal intraocular fluid drainage from the eye as a result of a blocked or defective trabecular meshwork (the mesh-like drainage canals in the eye). Congenital glaucoma may be due to an hereditary defect or abnormal development during pregnancy.
In other cases, an abnormal drainage system may be the result of some other disease in the eye which results in secondary glaucoma. In these cases, the glaucoma may be associated with recognizable iris (the coloured part of the eye), corneal, or other eye problems.
In an uncomplicated case of congenital glaucoma, microsurgery can often correct the structural defects. Other cases are treated with medication and surgery.