One of a leading cause of blindness among older people is known as glaucoma (G). It is a specific kind of diseases that damage the optic nerve, the big bundle of nerves that carries the images we see to the brain. As many people know, it has something to do with pressure inside the eye (intraocular pressure), and that the higher the pressure inside the eye, the greater the chance of damage to the optic nerve. It is not true, however, that high intraocular pressure (IOP) necessarily causes nerve damage, or that it is a major symptom or indicator.
What causes it?
Pressure builds up in the eye when the clear liquid called the aqueous humor, which normally flows in and out of the eye, is prevented from draining properly. This can happen in different ways, depending on the type of disease. The resulting increase in pressure within the eye can damage the optic nerve. Ophthalmologists used to think that high intraocular pressure was the main cause of optic nerve damage, however, we now know that even people with ”normal” IOP can experience vision loss – so-called ”normal tension glaucoma” (NTG). There may be other factors which affect the optic nerve, even when IOP is in the so-called ”normal” range. Elevated IOP is still considered a major risk factor, though, because studies have shown that the higher IOP is, then the more likely optic nerve damage to occur. Blindness results if the entire nerve is destroyed.
What are the Symptoms?
It is often is called the “silent thief of sight,” because most types typically cause no pain and produce no symptoms until noticeable vision loss occurs. For this reason, it often progresses undetected until the optic nerve already has been irreversibly damaged, with varying degrees of permanent vision loss. But with acute angle-closure glaucoma (ACG), symptoms that occur suddenly can include blurry vision, halos around lights, intense eye pain, nausea and vomiting. If you have these symptoms, make sure you see an eye care practitioner or visit the emergency room immediately so steps can be taken to prevent permanent vision loss.
There are several types of disease. The two main types are open-angle and angle-closure. These are marked by an increase of intraocular pressure (IOP), or pressure inside the eye.
The most common form of disease, accounting for at least 90% of all cases: is caused by the slow clogging of the drainage canals, resulting in increased eye pressure has a wide and open angle between the iris and cornea develops slowly and is a lifelong condition Has symptoms and damage that are not noticed. “Open-angle” means that the angle where the iris meets the cornea is as wide and open as it should be. Open-angle glaucoma (OAG) is also called primary or chronic. It is the most common type of disease, affecting about three million Americans.
A less common form of disease is caused by blocked drainage canals, resulting in a sudden rise in intraocular pressure has a closed or narrow angle between the iris and cornea. Develops very quickly has symptoms and damage that are usually very noticeable demands immediate medical attention. It is also called acute or narrow-angle G. Unlike open-angle, ACG is a result of the angle between the iris and cornea closing.
Also called low-tension or normal-pressure G. In it the optic nerve is damaged even though the eye pressure is not very high. We still don’t know why some people’s optic nerves are damaged even though they have almost normal pressure levels.
It occurs in babies when there is incorrect or incomplete development of the eye’s drainage canals during the prenatal period. This is a rare condition that may be inherited. When uncomplicated, microsurgery can often correct the structural defects. Other cases are treated with medication and surgery.
Variants of open-angle and angle-closure include: Secondary, Pigmentary, Pseudoexfoliative, Traumatic, Neovascular, Irido Corneal Endothelial Syndrome (ICE)
Screening and Tests for High IOP alone does not mean that you have it. Your doctor puts together many pieces of information to determine your risk for developing the disease. The most important of these risk factors include:
A family history.
Past injuries to the eye.
A history of severe anemia or shock.
Your doctor will weigh all of these factors before deciding whether you need treatment, or whether you should be monitored closely.
Methods of monitoring
Tonometer is used to measure your intraocular pressure (IOP Scanning laser polarimetry (SLP), Optical coherence tomography (OCT) Confocal scanning laser ophthalmoscopy – to create baseline images and measurements of the eye’s optic nerve and internal structures. Computer perimetry (SAP) Normally, IOP should be below 22 mmHg (millimeters of mercury) – a unit of measurement based on how much force is exerted within a certain defined area. If your IOP is higher than 30 mmHg, your risk of vision loss is 40 times greater than someone with intraocular pressure of 15 mmHg or lower. This is why the treatments such as eye drops are designed to keep IOP low.
Damage caused by G is, as a rule, not reversible, and no cure has yet been found. It can, however, be held in check with eye drops, pills, and laser or surgical operations that can be used to prevent or slow further damage from occurring. With any type of the disease, periodic exams are very important to prevent vision loss, even when treatment is successful. Because it can worsen without you being aware of it, your treatment may need to be changed over time. Treatment is focused on lowering IOP to a level the doctor thinks will not be likely to cause further damage in the optic nerve. This level (sometimes referred to as the ”target level”) varies from person to person and may even vary over time for an individual.
OAG is usually controlled with medicine that will lower the IOP and may take the form of pills, eye drops, ointments, or inserts (wafer-like strips placed in the corner of the eye). These medications reduce IOP by decreasing the production of aqueous humor or by increasing the flow through the drainage angle. The medications can have side effects, as can any medication. You should notify your doctor if you think you may be experiencing side effects including, but not limited to: a stinging sensation in the eyes, red eyes, blurred vision, headaches, changes in pulse, heartbeat or breathing, tingling of fingers and toes, drowsiness, loss of appetite, bowel irregularities, kidney stones, anemia or easy bleeding.
For many people, surgery may be the best treatment. There are several different types of surgery for G. The kind of surgery that is right for you will be determined by your doctor after considering a number of factors, including the type and severity of the disease, overall health, and other eye conditions. Depending on the type of surgery you and your doctor decide upon, it may be performed with either a laser or conventional surgical procedure.
The laser can be used in three different ways. Trabeculoplasty is used most often to treat OAG. In this procedure, a laser is used to place ”spot welds” in the drainage area of the eye, known as the trabecular meshwork, that allow the aqueous to drain more freely. Iridology is frequently used to treat ACG. In this procedure, the surgeon uses the laser to make a small hole in the iris, which allows the aqueous to flow more freely within the eye and through the trabecular meshwork. Cyclophotocoagulation is a slightly more drastic procedure which may be used to treat more advanced or aggressive cases of the disease. In this procedure, a laser beam is used to treat selected areas of the ciliary body, the part of the eye that produces aqueous humor, to reduce the production of fluid and thus lower the pressure within the eye. Laser surgery is usually performed in an outpatient surgery center or the doctor’s office and requires only light anesthesia and a generally short recovery time. Patients may experience some irritation in their eyes, but can usually resume their normal activities within one or two days.
In some cases, laser surgery is not the preferred surgical treatment. Sometimes, when vision loss is rapid, or medication and/or laser surgery fails to lower IOP sufficiently, ”conventional” incisional surgery is the best option. Filtering surgery is usually done with local anesthesia, and sometimes, sedation. The surgeon uses very delicate instruments to remove a tiny piece of the wall of the eye (the sclera), leaving a tiny hole. The aqueous can then drain through the hole and be reabsorbed into the bloodstream, thus reducing the intraocular pressure. In some cases, the surgeon may place a small tube or valve in the eye through a tiny incision in the sclera. The valve acts as a regulator for the buildup of aqueous within the eye. When the intraocular pressure reaches a certain level, the valve opens, allowing the fluid to flow out of the eye’s interior, where it can be reabsorbed by the body. The procedure can be done under local anesthesia. The recuperative period following incisional G surgery is usually short. You may need to wear an eye patch for a few days after surgery and to avoid activities which expose the eye to water, such as showering or swimming. The ophthalmologist may recommend you refrain from heavy exercise, straining, or driving for a short time after surgery to avoid complications. As with any surgery, patients should be aware that there are risks associated with it. Complications are not likely, but may include infection, bleeding, undesirable changes in IOP and in some cases, loss of vision. Sometimes, a single surgical procedure will not effectively halt the progress of a patient’s G. In these cases a repeat surgery may be scheduled and continued treatment by medication may be prescribed. Early detection, through regular and complete eye exams, is the key to protecting your vision from damage caused by G.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.
A Comprehensive Exam
To be safe and accurate, five factors should be checked before making a diagnosis:
Tonometry measures the pressure within your eye. During tonometry, eye drops are used to numb the eye. Then a doctor or technician uses a tool called a tonometer to measure the inner pressure of the eye. A small amount of pressure is applied to the eye by a tiny tool or by a warm puff of air. The range for normal pressure is 12-22 mm Hg (“mm Hg” refers to millimeters of mercury, a scale used to record eye pressure). Most cases are diagnosed with pressure exceeding 20mm Hg. However, some people can have G at pressures between 12 -22mm Hg. Eye pressure is unique to each person.
This diagnostic procedure helps the doctor examine your optic nerve for G damage. Eye drops are used to dilate the pupil so that the doctor can see through your eye to examine the shape and color of the optic nerve. The doctor will then use a small tool with a light on the end to light and magnify the optic nerve. If your intraocular pressure is not within the normal range or if the optic nerve looks unusual, your doctor may ask you to have one or two more exams: perimetry and gonioscopy.
Perimetry is a visual field test that produces a map of your complete field of vision. This test will help a doctor determine whether your vision has been affected by G. 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. Do not be concerned if there is a delay in seeing the light as it moves in or around your blind spot. This is perfectly normal and does not necessarily mean that your field of vision is damaged. Try to relax and respond as accurately as possible during the test. Your doctor may want you to repeat the test to see if the results are the same the next time you take it. After G has been diagnosed, visual field tests are usually done one to two times a year to check for any changes in your vision.
Gonioscopy this diagnostic exam helps determine whether the angle where the iris meets the cornea is open and wide or narrow and closed. During the exam, eye drops are used to numb the eye. A hand-held contact lens is gently placed on the eye. This contact lens has a mirror that shows the doctor if the angle between the iris and cornea is closed and blocked (a possible sign of angle-closure or acute G) or wide and open (a possible sign of open-angle, chronic G).
Pachymetry is a simple, painless test to measure the thickness of your cornea — the clear window at the front of the eye. A probe called a pachymeter is gently placed on the front of the eye (the cornea) to measure its thickness. Pachymetry can help your diagnosis, because corneal thickness has the potential to influence eye pressure readings. With this measurement, your doctor can better understand your IOP reading and develop a treatment plan that is right for you. The procedure takes only about a minute to measure both eyes.
Diagnosing the disease is not always easy, and careful evaluation of the optic nerve continues to be essential to diagnosis and treatment. The most important concern is protecting your sight. Doctors look at many factors before making decisions about your treatment. If your condition is particularly difficult to diagnose or treat, you may be referred to a specialist. A second opinion is always wise if you or your doctor become concerned about your diagnosis or your progress.