Glaucoma - Cause
Glaucoma is a
group of eye diseases that cause blindness by damaging the nerve cells located
in the back of the eye (the
optic nerve ). In many cases this damage to the optic nerve is thought to be
caused in part by increased pressure in the eye (intraocular pressure, or IOP) that results from the buildup of fluid inside the eye.
But damage often occurs without increased IOP.
eye anatomy and function.
open-angle glaucoma (OAG), the cause of damage to the
optic nerve is not well understood. Normally, the shape of the front part of
the eye (anterior chamber) is maintained by a fluid called
aqueous humor, which is produced in and removed from
the eye to maintain a constant pressure. Sometimes the aqueous humor does not
drain out of the eye normally, but the reason this occurs is not known. When
this happens, fluid builds up inside the eye, causing increased pressure within
the eye (IOP). Most people with open-angle glaucoma have higher-than-normal
IOP. The increased pressure inside the eye damages the optic nerve, resulting
in progressive loss of vision.
But not all people with open-angle
glaucoma have increased pressure inside the eye. Estimates vary, but as many as
40% to 50% of people with OAG may occur without increased IOP, and most people
with elevated pressures will never get glaucoma.1, 2 The first signs of this type of
glaucoma, referred to as normal or low-tension glaucoma, are changes within the
eye (enlarged cup-disc ratio) rather than increased pressure in the eye and
side (peripheral) vision loss.
Closed-angle glaucoma (CAG) occurs when
an already narrow
drainage angle for fluid in the eye becomes blocked.
This may occur when:
- The colored part of the eye (iris) and the lens
block the movement of fluid between the chambers of the eye. The blockage of
fluid causes pressure to build up in the eye and makes the iris press on the
eye's drainage system (trabecular meshwork). The increased pressure can cause damage to the optic nerve,
leading to vision loss and possible blindness.
- Defects in the iris
cause it to fall forward, blocking the drainage angle. Other factors, such as a
tumor, can force the iris forward, closing the drainage angle.
See a picture of
closed-angle glaucoma .
Congenital and infantile glaucoma
is present at birth (congenital glaucoma) or that develops in the first few years of life (infantile
glaucoma) is often caused by certain birth defects. A birth defect may develop
because of an infection in the mother during pregnancy, such as
rubella, or because of an inherited condition such as
Glaucoma may also develop as a
result of another condition. This is called secondary glaucoma.
- Glaucoma may develop after an eye injury, after
eye surgery, from the growth of an eye tumor, or as a complication of a medical
condition such as diabetes.
- Certain medicines (corticosteroids)
used to treat eye inflammation or other diseases may cause
- Glaucoma may develop as a result of the breakdown and
flaking off of the colored material (pigment) found in the colored part of the
eye (iris). This type of secondary glaucoma is called pigmentary glaucoma.
Another flaky material (of unknown origin) that can deposit in the anterior
part of the eye can cause a similar type of secondary glaucoma called
exfoliation syndrome (pseudoexfoliation).
cataract that causes swelling of the lens can cause
glaucoma (phacomorphic glaucoma). As the cataract develops, the eye's lens
thickens and closes the drainage angle, leading to an increase in intraocular
pressure (IOP). Medicines and possibly surgery may be used to relieve the
pressure. Removal of the cataract is usually necessary to treat phacomorphic