What is Glaucoma?
The optic nerve as Glaucoma progresses.
Glaucoma is caused by a number of different eye conditions which, in most cases, produce increased pressure within the eye. This elevated pressure is caused by a backup of fluid in the eye. Over time, it causes damage to the optic nerve. Through early detection, diagnosis and treatment, you and your optometrist can help to preserve your vision.
Think of your eye as a sink, in which the tap is always running and the drain is always open. The aqueous humor is constantly circulating fluid through the anterior chamber. It is produced by a tiny gland, called the ciliary body, situated behind the iris. It flows between the iris and the lens and, after nourishing the cornea and lens, flows out through a very tiny spongy tissue, only one-fiftieth of an inch wide (0.5mm), called the trabecular meshwork, which serves as the drain of the eye. The trabecular meshwork is situated in the angle where the iris and cornea meet. When this drain becomes clogged, aqueous can not leave the eye as fast as it is produced, causing the fluid to back up. But since the eye is a closed compartment, your `sink´ doesn´t overflow; instead the backed up fluid causes increased pressure to build up within the eye. We call this open (wide) angle glaucoma.
To understand how this increased pressure affects the eye, think of your eye as a balloon. When too much air is blown into the balloon, the pressure builds, causing it to pop. But the eye is too strong to pop. Instead, it gives at the weakest point & closes the fragile arteries supplying the optic nerve & causing these fibres to die.
As we mentioned earlier, the optic nerve is the part of the eye which carries visual information to the brain. It is made up of over one million nerve cells, and while each cell is several inches long, it is extremely thin -- about one twenty-thousandth of an inch in diameter. Their results in permanent visual loss. Early diagnosis and treatment of glaucoma can help prevent this from happening.
Types of Glaucoma.
There are a variety of different types of glaucoma. The most common forms are:
- Primary Open-Angle Glaucoma
- Normal Tension Glaucoma
- Angle-Closure Glaucoma
- Acute Glaucoma
- Pigmentary Glaucoma
- Exfoliation Syndrome
- Trauma-Related Glaucoma
Each has different causes and implications.
Glaucoma - Who is at Risk?
Everyone should be concerned about glaucoma and its effects. It is important for each of us, from infants to senior citizens, to have our eyes checked regularly, because early detection and treatment of glaucoma are the only way to prevent vision impairment and blindness. There are a few factors related to this disease which tend to put some people at greater risk:
People over the age of 45.
While glaucoma can develop in younger patients, it occurs more frequently as we get older.
People who have a family history of glaucoma.
People with abnormally high intraocular pressure (IOP). Latest evidence suggeststhese patients should be treated early.
High IOP is the most important risk factor for glaucomatous damage.
People of West African descent.
Afro-carribeans have a greater tendency for developing primary open-angle glaucoma than do people of other races.
Regular, long-term steroid/cortisone use.
A previous eye injury.
Glaucoma appears to `run´ in families. The tendency for developing glaucoma may be inherited. However, just because someone in your family has glaucoma does not mean that you will necessarily develop the disease.
Your optometrist has a variety of diagnostic tools which aid in determining whether or not you have glaucoma - even before you have any symptoms. Let us explore these tools and what they do.
OCT Optic Nerve Laser assessment: The most advanced instrument available to us for very early diagnosis. It measures the thickness of the top layer of the retina, the Nerve Fibre Layer, in microns. If this layer is different from the normative database, this indicates that there may well be Glaucoma. This is a very sensitive in strident and capable of comparing repeated measurements year after year to determine if there is progression in the disease.
The Tonometer: The Tonometer measures the pressure in the eye. If your optometrist were to use applanation tonometry, your eye would be anesthetized with drops. Then, you would sit at the slit lamp, and a plastic prism would lightly push against your eye in order to measure your IOP. In air tonometry a puff of air is sent onto the cornea to take the measurement. Since this instrument does not come in direct contact with your eye, no anesthetic eye drops are required.
Visual Field Test: Testing your visual field lets your optometrist know if and how your field of vision has been affected by glaucoma. The visual field is an important measure of the extent of damage to your optic nerve from increased IOP. There are several methods of examination available to your optometrist. In computerised visual field testing you will be asked to place your chin on a stand which appears before a computerised screen. Whenever you see a flash of light appear, you will be asked to press a button. At the end of this test, your optometrist will receive a printout of your field of vision. Another test which is similar is the Goldmann perimeter. However, in this test, no computer is used. The examiner records your answers whenever you indicate that the light is in view.
Ophthalmoscopy: Using an instrument called an ophthalmoscope, your optometrist can look directly through the pupil at the optic nerve. Its colour and appearance can indicate whether or not damage from glaucoma is present and how extensive it is. He may also use special lenses to obtain a three dimensional view.
Glaucoma can be treated with eyedrops, tablets, laser surgery, eye operations, or a combination of methods. The whole purpose of treatment is to prevent further loss of vision. This is imperative as loss of vision due to glaucoma is irreversible. Keeping the IOP under control is the key to preventing loss of vision from glaucoma. Your optometrist& ophthalmologist has several options for doing so. They include:
When medication does not achieve the desired results, or when it has intolerable side effects, your ophthalmologist may suggest eye surgery.
Routine eye exams are vital for protecting the health of your eyes. If your ophthalmologist or optometrist detects glaucoma, early treatment can help prevent the loss of your vision.