The Silent Vision Thief

Glaucoma, a leading cause of blindness, often goes undetected until eyesight is seriously impaired. Glaucoma is a disease of the eye in which there is increased pressure within the eyeball (intraocular pressure, or IOP).  Glaucoma occurs when the fluid (aqueous humor) in the front of the eye (between lens and cornea) cannot circulate due to obstructed drainage canals.  Fluid builds up, creating pressure on the fluid inside the eye (vitreous humor) and on the optic nerve, which results in impaired vision. Untreated, it results in gradual loss of vision because of damage to the optic nerve in the back of the eye.  This nerve consists of more than a million fibers that connect the retina-the light-sensitive layer of tissue at the back of the eye-to the brain.  

Glaucoma impairs the vision of more than 3 million Americans, half of whom are unaware that glaucoma is the source of their problem.  It is a 'silent' vision thief, because it steals your eyesight gradually without your knowing it.

A high IOP puts you at risk for glaucoma but does not necessarily mean you already have it.  Timely treatment can lower the pressure-and risk.

Another form of  glaucoma, much less common but more serious, is "acute-angle closure."  Here, the obstruction to the flow is sudden (instead of a slow buildup), resulting in the acute onset of blurred vision, pain in the eyes, headache, nausea and vomiting, rainbow halos when you look into a light-and sometimes blindness.  This is a medical emergency, because you can become totally blind within hours unless you're treated.

HOW THE PRESSURE BUILDS

The front of the eye contains a clear fluid called aqueous humor, which flows continuously in and out and prevents the interior of the eye from drying out. (This fluid has nothing to do with tears, which are made under the eyelid to keep the surface of the eye moist.)  The intraocular pressure level depends on the amount of fluid in the eye and whether it can circulate freely.  As we grow older, the drainage canals through which the fluid flows angle and constrict.  When they do so too much, fluid has trouble leaving the eye, backs up and causes increased intraocular pressure.  The result is "open-angle glaucoma," which accounts for 90% of cases.  A rising IOP does not usually cause any telltale symptoms or vision loss until a significant number of the optic nerve fibers have been damaged.

YOU SHOULD SUSPECT GLAUCOMA WHEN…

• You suddenly have no side vision.
  It's like looking through a tunnel.
   
• You have trouble adjusting from a brightly lit room to a darker one.
   
• Close-up work becomes difficult.
   
• You need to change prescriptions for glasses more frequently.
   
• You see colored rings if you look at bright lights.

WHO IS AT RISK?

• There is a history of glaucoma in your family.
   
• You are older than 60.
   
• You are African-American and over 40.
   
• You're diabetic.
   
• You've previously had some injury to your eyes.
   
• You are very nearsighted or farsighted.
   
• You've been using steroid medications, oral or inhaled, for any length of time.

HOW TO PROTECT YOURSELF

Regular eye examinations are the only way to detect increased eye pressure before vision is affected. Such an exam should include tonometry, which measures the actual pressure within the eye; gonioscopy, to evaluate the drainage angle; ophthalmoscopy, allowing the doctor to see the optic nerve; and perimetry, to test side vision.  Everyone over 40 should have these tests every two years.  They are critically important for seniors and African-Americans.

CONTROL IT WITH MEDICATIONS

Glaucoma cannot be cured, but there are medications and corrective procedures to prevent it from causing blindness.

The first goal is to lower intraocular pressure, usually done with eyedrops containing pilocarpine or carbachol. These drugs keep the drainage passages open and improve the flow of fluid out of the eye.  There is a membrane worn under the eyelid (Ocusert) that releases pilocarpine gradually over a five-day period.  Epinephrine compounds have the same effect but should be used with care if you have high blood pressure, heart trouble or any pulse irregularities.

Other kinds of eyedrops include beta-blockers, which reduce the rate at which fluid flows into the eye; alpha agonists, which reduce fluid production and increase out flow; and prostaglandin analogues, which expand a secondary drainage pathway. Carbonic anhydrase inhibitors, taken by mouth, reduce fluid flow into the eye.  Report any side effects to your doctor. If they're troublesome, you may need to reduce the dose or switch to another medication.

LASER THERAPY

If medications don't do the job, laser therapy (trabeculoplasty) enlarges the angle of the ducts in open-angle glaucoma.  It takes 10 to 20 minutes and is done in the doctor's office.  Eight out of 10 patients respond well to this treatment, and many eventually can stop taking eye medications. 

A laser treatment called (iridotomy) is used in acute-angle closure: A hole is created in the iris that permits the aqueous humor to flow more freely.  Iridotomy requires only local anesthesia and also can be done in the doctor's office.

SURGERY

The most common procedure is called a (Trabeculectomy).  Using miniature instruments, the surgeon removes a small piece of the drainage meshwork, leaving a tiny hole through which the aqueous humor can flow, thru reducing the pressure in the eye.  Unfortunately, about a third of patients develop cataracts within five years after this surgery, and 10% to 15% will need to have the operation done again.

None of these techniques restores lost vision, but they can keep matters from getting worse, and most patients are able to stop their glaucoma medications.

STAY ALERT

Glaucoma can sneak up without warning and rob you of your eyesight.  The only way to forestall blindness is to have regular comprehensive eye exams to measure the intraocular pressure.  So be smart. Get Tested.