Beware of Glaucoma

Glaucoma leads to blindness by damaging the optic nerve. Elevated pressure in the eye is a risk factor, but even people with normal pressure can lose vision to glaucoma.

What is Glaucoma?

Glaucoma is a group of eye diseases that gradually steal sight without warning. In the early stages of the disease, there may be no symptoms. Experts estimate that half of the people affected by glaucoma may not know they have it.Vision loss is caused by damage to the optic nerve. This nerve acts like an electric cable with over a million wires. It is responsible for carrying images from the eye to the brain.

There is no cure for glaucoma-yet. However, medication or surgery can slow or prevent further vision loss. The appropriate treatment depends upon the type of glaucoma among other factors. Early detection is vital to stopping the progress of the disease.It was once thought that high pressure within the eye, also known as intraocular pressure or IOP, is the main cause of this optic nerve damage. Although IOP is clearly a risk factor, we now know that other factors must also be involved because even people with “normal” levels of pressure can experience vision loss from glaucoma.

Anatomy of the Eye

A tough white covering called the sclera protects the eye. Part of the white sclera can be seen in the front of the eye. A clear, delicate membrane called the conjunctivacovers the sclera.

At the front of the eye is the cornea. The cornea is the clear part of the eye’s protective covering. It allows light to enter the eye. Theirisis the colored part of the eye that shrinks and expands so the pupil canlet just theright amount of light into the eye. The light is directed by thepupilto the lens. The lens focuses the light onto the retina (inside the lining of the nerve fibres in the retina carry images to the brain through the optic nerve.

The front part of the eye is filled with a clear fluid called intraocular fluid or aqueous humor, made by the ciliary body. The fluid flows out through the pupil. It is then absorbed into the bloodstream through the eye’s drainage system. This drainage system is a meshwork of drainage canals around the outer edge of the iris. 'Proper drainage helps keep eyepressureat a normal level'. The production, flow, and drainage of this fluid is an active continuous process that isneeded for the health of the eye.

The inner pressure of the eye (intraocular pressure or IOP) depends upon the amount of fluid in the eye. If your eye’s drainage system is working properly then fluid can drain out and prevent a buildup. Likewise, if your eye’s fluid system is working properly, then the right amount of fluid will be produced for a healthy eye. Your IOP can vary at different times of the day, but it normally stays within a range that the eye can handle.

The Eye With Glaucoma

In most types of glaucoma, the eye’s drainage system becomes cloggedso the intraocular fluid cannot drain. As the fluid builds up, it causes pressure to build within the eye. High pressure damages the sensitive optic nerve and results in vision loss.

The Optic Disc

You have millions of nerve fibers that run from your retina to the optic nerve. These fibers meet at the optic disc. As fluid pressure within your eye increases, it damages these sensitive nerve fibers and they begin to die. As they die, the disc begins to hollow and pushes the optic nerve into a cupped or curved shape. If the pressure remains too high for too long, the extra pressure can damage the optic nerve and result in vision loss.

Is There Another Cause?

It was once thought that high intraocular pressure (IOP) was the main cause of this optic nerve damage. Although IOP is clearly a risk factor, we now know that other factors must be involved because people with “normal” IOP can experience vision loss from glaucoma.

The Fluid Inside

Aqueous humor is the clear, watery fluid that is continually produced inside the eye. It is different from your tears. Tears are produced by glands outside of the eye and moisten the outer surface of the eyeball.

Early detection, through regular and complete eye exams, is the key to protecting your vision from damage caused by glaucoma.

It is important to have your eyes examined regularly. Your eyes should be tested:

• before age 40, every two to four years
• from age 40 to age 54, every one to three years
• from age 55 to 64, every one to two years
• after age 65, every six to 12 months

Anyone with high risk factors, should be tested every year or two after age 35.

Four Common Tests for Glaucoma

Regular glaucoma check-ups include two routine eye tests: tonometry and ophthalmoscopy.

Tonometry

The tonometry test measures the inner pressure of the eye. Usually drops are used to numb the eye. Then the doctor or technician will use a special device that measures the eye’s pressure.

Ophthalmoscopy

Ophthalmoscopy is used toexamine the inside of the eye, especially the optic nerve. In a darkened room, the doctor will magnify your eye by using an ophthalmoscope (an instrument with a small light on the end). This helps the doctor look at the shape and color of the optic nerve.

If the pressure in the eye is not in the normal range, or if the optic nerve looks unusual, then one or two special glaucoma tests will be done. These two tests are called perimetry and gonioscopy.

Perimetry

The perimetry test is also called a visual field test. During this test, you will be asked to look straight ahead and then indicate when a moving light passes your peripheral (or side) vision. This helps draw a “map” of your vision.

Gonioscopy

Gonioscopy is a painless eye test that checks if the angle where the iris meets the cornea is open or closed, showing if either open angle or closed angle glaucoma is present.

Optic Nerve Computer Imaging

In recent years three new techniques of optic nerve imaging have become widely available. These are scanning laser polarimetry (GDx), confocal laser ophthalmoscopy (Heidelberg Retinal Tomography or HRT), and optical coherence tomography (OCT).

The GDx machine does not actually image the optic nerve but rather it measures the thickness of the nerve fiber layer on the retinal surface just before the fibers pass over the optic nerve margin to form the optic nerve. The HRT scans the retinal surface and optic nerve with a laser. It then constructs a topographic (3-D) image of the optic nerve including a contour outline of the optic cup. The nerve fiber layer thickness is also measured. The OCT instrument utilizes a technique called optical coherence tomography which creates images by use of special beams of light. The OCT machine can create a contour map of the optic nerve, optic cup and measure the retinal nerve fiber thickness. Over time all three of these machines can detect loss of optic nerve fibers.

Your intraocular eye pressure (IOP) is important to determining your risk for glaucoma. If you have high IOP, careful management of your eye pressure with medications can help prevent vision loss. Recent discoveries about the cornea, the clear part of the eye’s protective covering, are showing that corneal thickness is an important factor in accurately diagnosing eye pressure. In response to these findings, the Glaucoma Research Foundation has put together this brief guide to help you understand how your corneal thickness affects your risk for glaucoma, and what you can do to make sure your diagnosis is accurate.

In 2002, the five-year report of the Ocular Hypertension Study (OHTS) was released. The study’s goal was to determine if early intervention with pressure lowering medications could reduce the number of ocular hypertensive (OHT) patients that develop glaucoma. During the study, a critical discovery was made regarding corneal thickness and its role in intraocular eye pressure and glaucoma development.

Why is Corneal Thickness Important?

Corneal thickness is important because it can mask an accurate reading of eye pressure, causing doctors to treat you for a condition that may not really exist or to treat you unnecessarily when are normal. Actual IOP may be underestimated in patients with thinner CCT, and overestimated in patients with thicker CCT. This may be important to your diagnosis; some people originally diagnosed with normal tension glaucoma may in fact be more accurately treated as having regular glaucoma; others diagnosed with ocular hypertension may be better treated as normal based on accurate CCT measurement. In light of this discovery, it is important to have your eyes checked regularly and to make sure your doctor takes your CCT into account for diagnosis.

A Thin Cornea—The Danger of Misreading Eye Pressure

Many times, patients with thin corneas (less than 555 µm) show artificially low IOP readings. This is dangerous because if your actual IOP is higher than your reading shows, you may be at risk for developing glaucoma and your doctor may not know it. Left untreated, high IOP can lead to glaucoma and vision loss. It is important that your doctor have an accurate IOP reading to diagnose your risk and decide upon a treatment plan.

A Thicker Cornea May Mean Less Reason to Worry About Glaucoma

Those patients with thicker CCT may show a higher reading of IOP than actually exists. This means their eye pressure is lower than thought, a lower IOP means that risk for developing glaucoma is lowered. However, it is still important to have regular eye exams to monitor eye pressure and stay aware of changes.

Pachymetry—A Simple Test to Determine Corneal Thickness

A pachymetry test is a simple, quick, painless test to measure the thickness of your cornea. With this measurement, your doctor can better understand your IOP reading, and develop a treatment plan that is right for your condition. The procedure takes only about a minute to measure both eyes.

Four Key Facts About Glaucoma

Glaucoma is a leading cause of blindness.

Glaucoma can cause blindness if it is left untreated. And unfortunately approximately 10% of people with glaucoma who receive proper treatment still experience loss of vision.

There is no cure (yet) for glaucoma

Glaucoma is not curable, and vision lost cannot be regained. With medication and/or surgery, it is possible to halt further loss of vision. Since glaucoma is a chronic condition, it must be monitored for life.

Diagnosis is the first step to preserving your vision.

Everyone is at risk for glaucoma

Everyone is at risk for glaucoma from babies to senior citizens. Yes, older people are at a higher risk for glaucoma but babies can be born with glaucoma (approximately 1 out of every 10,000 babies born in the United States).

Young adults can get glaucoma, too. African-Americans in particular are susceptible at a younger age.

There may be no symptoms to warn you

With open angle glaucoma, the most common form, there are virtually no symptoms. Usually, no pain is associated with increased eye pressure.

Vision loss begin with peripheral or side vision. You may compensate for this unconsciously by turning your head to the side, and may not notice anything until significant vision is lost. The best way to protect your sight from glaucoma is to get tested. If you have glaucoma, treatment can begin immediately.

Glaucoma is a very misunderstood disease. Often, people don’t realize the severity or who is affected. I hope the above information is helpful to you.