Glaucoma is a condition in which the eye pressure, also known as intra-ocular pressure (IOP), is too high for a given eye and thus causes damage to the optic nerve of that eye. (Note: each individual has a different pressure which causes damage to the optic nerve) Damage to the optic nerve results in progressive loss of peripheral or side vision. Central or straight ahead vision is preserved until the end of the disease (tunnel vision). Pressure is measured in mm of Hg (mercury). Normal pressure is between 10 – 21 mm Hg with 14 being the average. Prior to 1978, glaucoma was defined as a disease in which the pressure was above 21 mm Hg in an eye.
Today we know that this is not correct. Only 10-20% of the patients having an eye pressure between 21-24 mm Hg go on to develop loss of the peripheral vision or loss of side vision over a ten year period of time. Fifty percent loose peripheral vision if their pressure is consistently between 25-27 mm Hg, and 90% loose vision if the pressure is 30 mm Hg. The natural history of patients that have non-treated glaucoma is slow progression. Glaucoma is usually a slow disease.
Untreated glaucoma takes on an average of 15 years to progress from early damage to blindness with an IOP of 21 to 25 mmHg, 7 years with 25 to 30 mmHg, and 3 years with a pressure more than 30 mmHg. Thus, most eye doctors will treat a pressure over 30 with out signs of damage. We tend to treat a little earlier.
Like blood pressure the eye pressure (intra-ocular pressure) will vary from day to day and time of day, usually higher in the morning and lower in the early evening. Therefore, it is important to measure the pressure at different times of the day. Patients without glaucoma may vary 4 mm Hg while patients with glaucoma tend to vary more. This variability necessitates multiple readings at different times of the day before making any decision. Unless the pressure is very high, one reading is meaningless. In addition, it takes years for the pressure to damage the eyes, thus, time is on our side. One should use the time to make an appropriate decision without panicking.
What Causes the Increase in Eye Pressure?
The truth is that we are not sure. Either we make too much fluid, have restricted drainage or the (“thermostat”) control system does not maintain a proper pressure. Treatment is directed at either decreasing production of the aqueous (the fluid in the front part of the inside of the eye) or increasing the out flow. This is analogous to your sink, to maintain a constant level of water in the sink one must control the amount of water going into the sink or increase the size of the holes in the drain. Which ever mechanism is causing the increase in pressure, treatment today is directed towards reducing pressure. Newer thoughts suggest that blood flow to the nerve may be as important as pressure. Also, newer drugs may provide neuro-protection (slow down the death process). The only thing that has shown to slow the progression of glaucoma is control of eye pressure.
Is Glaucoma Always Due to High Pressure in the Eye?
There is a small group of people who loose vision with consistent pressure under 21mm Hg. This condition is known as normal or low tension glaucoma and is the most dangerous type of glaucoma in patients who do not have routine eye examinations. There are few signs or symptoms for the patient or doctor to determine the presence of the condition. It is often first suspected if one or both of the nerves look unusual. Glaucomatous appearing nerves or nerves that appear differently in each eye must be carefully watched to make sure that this uncommon disease is not present. Watching includes observation of the nerve, measurement of pressure, and repeating peripheral field testing (visual fields). Glaucomatous appearing nerves may be normal for a given individual. Change over time demonstrates the presence of glaucoma.
At What Age Do You Begin Taking Eye Pressure?
We attempt to take pressure on every patient. In very young children we do this by touching the eye. Glaucoma is rarely present in the young, but becomes more common after age 35. The chances of developing glaucoma increase with age. Glaucoma is found in 2% of whites and 7% of blacks older than age 65. Thus, it is a common eye disease.
Do the Drops Taken for Glaucoma Cure Glaucoma?
No. Glaucoma is similar to high blood pressure. The drops control the pressure. Stop the drops and the pressure re-occurs. It is important to continue the glaucoma eye drops for another reason. Many believe that variability of pressure is more dangerous than if constantly high. One must be committed to a life long treatment. Laser treatment can eliminate the need for drops for some. Laser treatment is effective in 80% of the patients with glaucoma but wears off in about half in 5 years. It can be repeated. Most doctors begin treatment of glaucoma with drops, but would begin treatment of them with laser! Surgery, which is successful, is reserved for the few in which either the drops or laser do not effectively control the pressure. Laser and surgery can also be used in the non-compliant patient.
The tough part in the treatment of glaucoma is to get the patient to use the drops consistently even though they have no visual disturbance- they see fine. The drops can have side effects, which makes it even harder for the patient to continually take their drops. The drops prevent further damage they do not restore vision already lost. If you are bothered by the drops, do not stop taking the drops, call the doctor.
If I Have Normal Pressure Can I Be Assured That I Don’t Have Glaucoma?
No. One third of the people who have glaucoma will have a normal eye pressure at the time of their examination. Thus, eye pressure is not the only determinate for glaucoma but a risk factor. Other risk factors include: age, family history of glaucoma, corneal thickness, myopia, being African-Americans, having diabetes, hypertension, or other vascular disease, e.g., migrane. If the risk factors are too great, we may elect to treat the patient though the disease is not proven to present (risk against benefit). The goal is not to over or under treat the condition. Treatment includes drops, simple office based laser treatment, and rarely surgery. The goal of treatment is to lower the pressure so that the pressure will not cause further damage. Thus, the treatment will not make you see better nor feel better. The target pressure varies from patient to patient depending on the entering pressure, current damage, and/or risk factors.
I Have Heard That there are Two Types of Glaucoma?
Actually there are many types of glaucoma but two major categories. One in which the pressure increases insidiously over time and is moderately high. This type is known as chronic or primary open angle glaucoma. The higher pressure results from an inaccurate control system like the thermostat of your house being set to high. Another analogy would be that too much water is coming out of a faucet vs. being drained. This increased pressure is painless and asymptomatic until the late stages, which, makes it dangerous. Open angle glaucoma is diagnosed by pressure, risk factors, appearance of the optic nerve, and results of the visual fields test. Approximately one percent of all Americans have this form of glaucoma, making it the most common form of glaucoma. It occurs mainly in patients over 50. The danger of this disease is its silence. Generally, there is no pain associated with glaucoma. By the time the vision is impaired, the damage is irreversible.
The second category is the narrow angle glaucoma. In this condition, the eye is anatomically small causing the iris (colored part of your eye) to bow forward. Before an attack the drainage is normal and pressure is normal. With age the angle or space between the corneas narrows. During an attack, incorrect, positioning of the iris causes the drainage system to become blocked. Closure is analogous to dropping a plug into the drain of a sink. The result – a rapid increase in pressure. The pressure may rise from normal mid-teens to 40-70. The eye becomes red, painful, with blurred vision or halos around lights. Often the pupil is dilated. Nausea and headache may accompany the increase in pressure. Angle-closure glaucoma affects nearly half a million people in the United States. There is a tendency for this disease to be inherited. It is more common in people of Asian descent and people who are far-sighted.
This is an ocular emergency if not taken care of immediately. Severe permanent loss of vision may occur. Fortunately, the predisposition to this type of glaucoma is easily detected during a comprehensive eye exam. If the chances of closure in the future are significant then a laser is used to prophalaxically create another exit via the iris, like the overflow drain in your sink. This laser treatment is simple and painless without a true recovery time. If the angle is known to be dangerously narrow one should avoid medications which cause dilation of the pupil and may lead to an attack of glaucoma. These include anti-depressants, cold medications, antihistamines, and some medications to treat nausea. The labels of these medications usually which state “does not take if you have glaucoma”. Unfortunately, the patients with un-diagnosed narrow angle glaucoma are the ones at risk if they use these medications. Acute glaucoma attacks are not always full blown. Sometimes patients have numerous minor attacks. The patient might experience slight blurring of vision and/or haloes of light, with or without pain or redness. Once the laser is performed this type of glaucoma is cured.
What Happens if I Have Glaucoma and Exercise?
Exercise seems to lower IOP and therefore decreases the risk of glaucomatous damage. There are two exceptions: standing on ones head which increases blood flow to the head, also, increases pressure within the eye; and secondly, pigmentary glaucoma is also aggregated by physical exercise.
What Are Some of the Other Types of Glaucoma?
Traumatic glaucoma – after injury, if bleeding in the eye occurred the pressure rise may occur yrs. later
Uveitic glaucoma – associated with iritis
Pseudo Capsular Exfoliation – found more commonly in Russians, Scandinavians and Eskimos
Pigmentary Glaucoma – found more commonly in young men (Kruckenberg spindle increases the incidence)
Steroid Induced Glaucoma – a result of steroid pills or drops, e.g., prednisone
Neo-vascular Glaucoma- found in diabetes, after occlusion of the main vein of the eye, severe ischemia
Will I Go Blind from Glaucoma?
If you have routine examinations and you develop glaucoma, the chances of serious vision loss from glaucoma are very remote. However, late detection or non-compliance may result in vision loss. One may think of glaucoma being analogous to a house on the beach. If a house is in good shape and is hit by a series of storms, then the house will survive the storms with little damage (high eye pressure with a healthy nerve). However, if the foundation of the house has been damaged by previous storms there is a significant chance that the house will either be further damaged or swept away by the storm (a damaged nerve can not take the excess pressure from glaucoma). Thus, the key to preserving vision is early detection with aggressive treatment. The chronic, progressive nature of the disease makes it difficult for the patient to faithfully take their medication – the key to preserving vision.
What Tests Show Damage?
Visual fields tests measure side or peripheral vision. Glaucoma causes loss of peripheral or side vision before central vision. It is not until late into the disease is that central or visual acuity is effected. The problem is that defects in visual fields do not show up until glaucoma is relatively advanced (over 50% of the nerve fibers must be lost before visual fields changes).
Once visual fields changes are noted it is very sensitive to progression. Even with perfect control of eye pressure, a very, few patients will continue to loose fields. This occurs only in very advanced glaucoma. Previously, the best method for monitoring early glaucoma was careful evaluation of the optic nerve. As long as the nerve doesn’t change, there is no progression. Newer, tests use laser scanning (HRII) to create a three dimensional picture of the optic nerve. The scanning lasers are accurate and quantitative than the doctor just observing the nerve. These tests may replace visual field testing in detecting early glaucoma in the future. Late glaucoma is best followed with visual fields testing.
What Are The Results of the Ocular Hypertensive Study and What Do They Mean to Me?
This study investigated the effect of treating patients who half elevated pressure without any evidence of damage to the nerve or an abnormal visual field. These Patients have been called ocular hypertensives or glaucoma suspects. Until this study, no one knew the natural history of patients with elevated pressure without damage. Half the subjects were treated with eye drops while the other half were watched. Eye drops reduced the development of glaucoma by over 50% in a study of 1636 people with elevated eye pressure without evidence of damage, i.e., normal optic nerve and visual field. Nine and a half percent of those who were watched developed glaucoma after five years, while only 4.4% of those treated with drops developed glaucoma.
If you have above-average eye pressure you don’t necessarily need to begin taking eye drops. Not everyone with elevated eye pressure develops glaucoma; in this study, over 90% of those in the untreated group did not show any evidence of damage during the five years of the study. Those of you who are at moderate or high risk of developing glaucoma should be treated.
This study also demonstrated that traditional methods of measuring your eye pressure are more dependent on the thickness of your cornea than previously thought. Thin corneas measure lower pressures while thicker corneas measure higher pressure. If you are at risk of developing glaucoma or have it we will measure the thickness of your cornea. —June 2002 issue of Archives of Ophthalmology.