GLAUCOMA, Open Angle
What is Glaucoma?
Glaucoma is a group of diseases that cause damage to the optic nerve. Optic nerve damage can eventually lead to visual loss, even blindness. Usually, with early detection and intervention this disease can be arrested and visual loss can be circumvented.
The Optic Nerve:
The hundreds of millions of fibers of the peripheral retina coalesce as they advance toward the optic nerve. By the time they form the optic nerve, there are roughly 1.2 million fibers that communicate between the eye and the brain.
The information flow is bidirectional - information goes from the eye to the brain and from the brain to the eye.
OPEN ANGLE GLAUCOMA:
Glaucoma represents optic nerve damage; usually this damage is due to the pressure of the eye being too high.
While OPEN ANGLE GLAUCOMA is often associated with high eye pressure (IOP) the pressure does not necessarily need to be above normal. When the optic nerve becomes damaged while the eye pressure (IOP) is normal, that type of glaucoma is termed NORMAL PRESSURE (or, NORMAL TENSION) GLAUCOMA.
The eye constantly makes a clear fluid, the AQUEOUS HUMOR, that is generated in the CILAIRY BODY behind the colored part of the eye (iris) and flows around the LENS, through the PUPIL and into the ANTERIOR CHAMBER.
The AQUEOUS HUMOR exits the ANTERIOR CHAMBER at the angle where the cornea and iris meet. (click diagram for video)
In open-angle glaucoma the fluid passes too slowly through the drainage system and the eye pressure may rise. Even if the pressure is still within the normal range, the pressure may become higher than is healthy for the particular eye's optic nerve. The optic nerve may become damaged and vision loss may result.
INCREASED EYE PRESSURE DOES NOT NECESSARILY EQUAL GLAUCOMA
Not every person with increased eye pressure will develop glaucoma. Some people can tolerate higher levels of eye pressure better than others. A comprehensive dilated eye exam is very important to help determine how well your optic nerve tolerates your eye pressure.
WHO IS AT RISK FOR OPEN ANGLE GLAUCOMA:
Who is at risk for open-angle glaucoma?
Anyone can develop glaucoma. A recent study helped to define specific risk factors that augment this likelihood:
· African Americans over age 40
· Everyone over age 60
· People with a family history of glaucoma
· People with diabetes
· People with high blood pressure
· Nearsighted individuals (myopia)
· People with thin corneas
· People with asymmetric optic nerve cups
· Steroid use
· High eye pressure (IOP)
What are the symptoms of Glaucoma?
Glaucoma does not have symptoms in the early stages.
The optic nerve has twice as many fibers as it needs to maintain a full field of vision.
Therefore, more than half of the fibers can be lost to glaucoma and the patient will not notice any changes.
Even after early changes in the peripheral vision do occur, these can be so insidious that the patient will have no clue.
Gradually, as more optic nerve fibers are lost, the VISUAL FIELD will become compromised and the glaucoma patient may observe reduced peripheral vision or incomplete vision.
Sadly, this is already an advanced state of the disease.
How is glaucoma detected?
Glaucoma is primarily detected through a comprehensive ophthalmic evaluation.
Each parameter of the eye test helps to identify and quantify a person's risk for or stage of glaucoma.
The patient's inability to sense glaucoma until the disease is far advanced makes routine eye exams invaluable.
This test measures how well you see at various distances.
This may include REFRACTION, or an examination for glasses to determine the patient's 'best-corrected' visual acuity.
Tonometry measures the pressure inside the eye. The 'contact' technique is preferred over the "puff" technique. Contact or APPLANATION TONOMETRY is far more accurate and avoids the 'puff' that people loathe.
The intraocular pressure varies throughout the day; therefore it can be revealing to monitor a person's pressure at different times of the day over sevral visits in order to detect higher pressures than might be discovered on routine visits at tyically convenient hours.
DIlated Eye Exam:
The dilated exam allows direct visualization of the optic nerve and the retina (the FUNDUS).
Evaluation of the shape, contour, color and symmetry of the optic nerves is critical to diagnosing and monitoring glaucoma.
Dilation also facilitates other measurements for glaucoma, like ultrasound, and photography.
Visual Field Testing:
Also known as PERIMETRY, this test quantifies the function of the optic nerve.
Unlike other tests, this method assesses what the patient sees and can illustrate the impact that glaucoma is having on one's visual function.
Optical Coherent Tomography (OCT):
OCT is a form of ULTRASOUND that measures the optic nerve's physical contours.
This, in turn, enables the examiner to compare an individual's optic nerve parameters to his/her cohort group.
In addition, this measurement serves as a parameter with whch to monitor an individual's own optic nerve stability.
Pachymetry is a method of measuring the thickness of a patient's cornea.
Studies have shown that the measurement of pressure of the eye may vary based on the corneal thickness.
Determining a particular patient's corneal thickness (PACHYMETRY) helps calibrate the pressure measures to the 'real' eye pressure.
Can glaucoma be cured?
No. There is no cure for glaucoma. When vision is lost from glaucoma, it cannot be restored.
Immediate treatment for early-stage, open-angle glaucoma can prevent progression of the disease.
Glaucoma treatments include medicines, laser trabeculoplasty, conventional surgery, or a combination of any of these.
While these treatments may save remaining vision, they do not improve sight already lost from glaucoma.
Medicines, in the form of eye drops or pills, are the most common early treatment for glaucoma. Glaucoma medicines need to be taken regularly as directed by your ophthalmologist.
Before you begin glaucoma treatment, tell your ophthalmologist about other medicines and supplements that you are taking. Sometimes the drops, or pills, can interfere with the way other medicines work.
Side effects may include stinging, burning, and redness in the eyes.
Many medicines are available to treat glaucoma. If you have problems with one medicine, tell your ophthalmologist. Treatment with a different dose or a new medicine may be possible.
Laser trabeculoplasty helps fluid drain out of the eye. Your ophthalmologist may suggest this step at any time.
In many cases, you will need to keep taking glaucoma medicines after this procedure.
Laser trabeculoplasty is performed in the office. A beam of light is aimed through a lens and reflected onto the meshwork inside your eye. This allows the fluid to drain better.
Laser can cause side effects such as inflammation. Drops for soreness or inflammation may be prescribed.
If you have glaucoma in both eyes, usually only one eye will be treated at a time.
Studies show that laser surgery can reduce the pressure in some patients. However, its effects can wear off over time and you may require further treatment.
Conventional 'filtering' surgery makes a new opening for the fluid to leave the eye.
Conventional surgery is usually done after medicines and laser surgery have failed to control pressure.
Trabeculectomy, is performed in an operating room. A small piece of tissue is removed to create a new channel for the fluid to drain from the eye through a "filtration bleb."
Surgery is performed on one eye at a time and is about 60 to 80 percent effective at lowering eye pressure.
What are some other forms of glaucoma and how are they treated?
Low-tension or normal-tension glaucoma:
Glaucomatous damage to the optic nerve can occur in people who do not manifest eleavted intraocular pressures.
This form of LOW TENSION GLAUCOMA is particualrly challenging because in contrast to patients with high pressure, it is difficult to achieve a meaningful reduction in pressure in patients with normal eye pressure.
A comprehensive medical history is important to identify other potential risk factors, such as low blood pressure, that contribute to low-tension glaucoma. If no risk factors are identified, the treatment options for low-tension glaucoma are the same as for open-angle glaucoma, but the approach must be more aggessive and the patient must be monitored very closely.
Symptoms may include severe pain and nausea, as well as redness of the eye and blurred vision. If you have these symptoms, you need to seek treatment immediately. This is a medical emergency. Without treatment to restore the flow of fluid, the eye can become blind.
Usually, prompt laser surgery and medicines can clear the blockage, lower eye pressure, and protect vision.
If the ophthalmologist detects a predisposition to this condition, laser iridotomy may be recommended to prevent a narrow angle glaucoma attack.
The fluid that is made behind the iris must flow around the lens and through the pupil to leave the eye via the anterior chmber.
In people with small eyes, like far-sighted patients, the anterior chamber becomes crowded as the person lives and the lens gets thicker.
As this process continues, the angle gets blocked by part of the iris. People with this type of glaucoma may have a sudden increase in eye pressure.