What is Glaucoma?
Glaucoma is a serious eye condition that can cause blindness. It damages the optic nerve, which carries information from your eyes to the visual center in your brain. This damage can result in permanent vision loss.
The most common type of glaucoma has no early warning signs and can only be detected during a comprehensive eye exam. If undetected and untreated, glaucoma first causes peripheral vision loss and eventually can lead to blindness.
By the time you notice vision loss from glaucoma, it’s too late. The lost vision cannot be restored, and it’s very likely you may experience additional vision loss, even after glaucoma treatment begins.
What Causes Glaucoma?
In most cases, glaucoma is caused by higher-than-normal pressure inside the eye — a condition called ocular hypertension.
But sometimes glaucoma can occur even when pressure inside the eye — called intraocular pressure
or “IOP” — is normal.
The space between the clear front surface of the eye (the cornea) and the lens inside the eye is filled with a clear fluid called the aqueous humor. This fluid nourishes the inside of the anterior part of the eye. It also maintains the shape of the eye by keeping the eyeball properly pressurized.
The aqueous humor is constantly being produced by a structure called the ciliary body that surrounds the lens, and it drains from the eye through a mesh-like channel called the trabecular meshwork that’s located in the angle formed inside the eye where the cornea and iris meet.
If something causes this “drainage angle” to close down or the trabecular meshwork to become clogged, the aqueous humor cannot drain from the eye fast enough, and pressure inside the eye (IOP) increases.
Glaucoma usually occurs when too much pressure inside the eye causes damage to the optic nerve at the back of the eyeball, leading to permanent vision loss.
Recent studies also have implicated low intracranial pressure (the pressure that surrounds the brain) as one of the risks for glaucoma.
Most types of glaucoma typically cause no pain and produce no symptoms until noticeable vision loss occurs.
This is one reason why routine eye exams are so important — typically, an eye exam is the only way to detect glaucoma before permanent vision loss occurs.
However, a less common type of glaucoma — called acute angle-closure glaucoma — causes sudden, often severe symptoms of blurry vision, halos around lights, eye pain, nausea and vomiting.
If you experience these symptoms, see an eye doctor near you immediately so steps can be taken to reduce your IOP, alleviate symptoms and prevent permanent vision loss.
Types of Glaucoma
The two main types of glaucoma are:
Primary Open-Angle Glaucoma : This is the most common type of glaucoma and typically is the type that eye doctors describe to their patients. In primary open-angle glaucoma (POAG), the drainage angle that leads to the trabecular meshwork looks normal, but aqueous fluid exits the eye too slowly.
Angle-Closure Glaucoma : This is a less common type of glaucoma where the drainage is too narrow or begins to close, impeding the normal outflow of aqueous humor.
Angle-closure glaucoma can be either chronic (an anatomically narrow angle or temporary episodes of angle closures over time) or acute (the angle narrows or closes suddenly).
The term narrow-angle glaucoma often is used to describe glaucoma that occurs when the drainage angle is too small or is partially closed.
Other Glaucoma Types
Other types of glaucoma include:
Low-tension or Normal-Tension Glaucoma : In these types of glaucoma, optic nerve damage and vision loss occurs even though IOP remains normal. Low blood pressure may be a risk factor.
Congenital Glaucoma : Some children are born with a defect in the drainage angle that prevents the aqueous fluid from exiting the eye normally. Usually there are obvious symptoms, such as cloudy corneas, light sensitivity and watery eyes.
Secondary Glaucoma : This type of glaucoma develops due to complications of certain medical conditions (including diabetes and high blood pressure) or because of other eye conditions (such as cataracts and uveitis), side effects of medications, or trauma to the eye.
Detecting Glaucoma : During routine eye exams, a small instrument is used to measure your intraocular pressure (IOP). During this test (called tonometry), eye drops may or may not be used to make your cornea less sensitive.
Normal IOP typically is considered to be readings below 21 mmHg (millimeters of mercury) — a unit of measurement based on how much force is exerted within a certain defined area.
Higher IOP readings indicate increased risk of glaucoma.
Other methods of detecting glaucoma involve the use of sophisticated imaging technology to create baseline images and measurements of the eye’s optic nerve and internal structures. These images and measurements are then repeated at successive eye exams to check for changes.
There are several types of glaucoma treatment, including medicated eye drops, micro-surgery, laser treatments and other eye surgery.
It’s important to realize that glaucoma treatments may prevent additional vision loss, but they will not restore vision already lost to the disease.
Depending on the type, severity and responsiveness of your glaucoma to treatment, your eye doctor may prescribe medical treatment, surgery or a combination of both.