Lowering Intraocular Pressure
March 15, 2006
Norma Devine, Editor
On Wednesday, March 15, 2006, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed “Lowering Intraocular Pressure.”
Moderator: Tonight our topic is “Lowering Intraocular Pressure.” Why is lowering intraocular pressure (IOP) important?
Dr. Rick Wilson: IOP seems to be the main risk factor for glaucoma that we can do much about. Many studies now have proved the link between IOP and the probability of glaucoma progression.
P: How does the doctor decide the best range of pressure for a particular patient?
Dr. Rick Wilson: The decision is based upon (1) how much damage the nerve has sustained, (2) at what pressure the damage occurred, (3) whether the patient would be expected to become visually symptomatic during his or her lifetime at the present rate of loss, (4) whether there are systemic risk factors, usually circulatory (that is, blood flow that may put the patient more at risk), and (5) whether there is a family history to help with judging the patient’s susceptibility to IOP.
P: How long does it take for glaucoma medication to reach its maximum potential?
Dr. Rick Wilson: Most glaucoma medications reach the maximum IOP lowering effect in about two hours. The prostaglandins (e.g., Travatan, Xalatan, and Lumigan) take longer. In some people, there may be small gains in effectiveness even after a week.
P: Do some groups of people respond better to certain intraocular-lowering treatments than others?
Dr. Rick Wilson: Yes. As a rule, people with inflammatory glaucoma do not respond to prostaglandins. In children, prostaglandins have a much more sporadic effect. Beta blockers do not work at all in 10% of the population, etc.
P: Does exercise lower IOP as much as one medication?
Dr. Rick Wilson: Aerobic exercise for twenty minutes or more four times a week is said to lower IOP as much as one medication.
Moderator: Is it true that aerobic exercise (a heart rate above 120 beats per minutes for at least 20 minutes) is the only known non-medicinal or non-surgical way to lower IOP?
Dr. Rick Wilson: It is the only one I can think of that is practical at the moment.
P: Why does aerobic exercise help lower IOP?
Dr. Rick Wilson: The increased CO2 helps immediately by increasing the size of the vessels and lowering blood pressure. It is not as clear how the effect continues in between exercise.
P: What do you think of the claims that eye exercises and herbal and vitamin supplements promote healthier eyes?
Dr. Rick Wilson: Body exercise helps. Anything more than reading, which lowers IOP somewhat, is a waste of time. I usually recommend a good multivitamin with minerals for women and, without iron, for men. If they want to be aggressive, an aspirin taken with their doctors’ approval is believed by many to help. I also take 200 IU vitamin E and 500 IU vitamin C each morning, but the vitamin E is now controversial.
Moderator: How is normal-tension glaucoma (NTG) explained?
Dr. Rick Wilson: We cannot explain NTG well. It seems as if there is more than one risk factor involved. If the IOP is high, that is all the risk you need. If the IOP is not high, perhaps low systemic blood pressure is involved, or the regulation of blood flow to the optic nerve is poor, or the need is greater.
P: Could increased blood flow to eyes cause glaucoma?
Dr. Rick Wilson: An abnormal pressure in the veins around the eye leads to an immediate increase in IOP. If the flow is above normal, but not at a higher pressure, I am not sure that it would raise your IOP.
P: Are cold feet considered to be a systemic blood flow problem?
Dr. Rick Wilson: Yes, cold hands and feet are often a sign of impaired circulation that may also be present in the optic nerves. The body regulates blood flow, depending upon the needs of the tissue in question. If you exercise or use an organ, the blood flow should increase. If it does not, that is a sign of dysregulation. Patients with glaucoma do not seem to be able to adjust their blood flow to the optic nerves as normally as most people.
P: Why do eyedrops that lower IOP sometimes stop working after having worked so well?
Dr. Rick Wilson: Beta blockers, for example, block beta tone to the beta receptors in the eye. In response, the eye may just increase the number of beta receptors if it doesn’t get the expected amount of tone. Prostaglandins seem to show the least drop-off in effectiveness. Often, however, the medicine is working as well as it always had, but the disease has become worse.
P: I had a tube shunt procedure in December. The tube opened at six weeks, but my IOP is still in the range of 22 to 25 mm Hg, even though I am on Cosopt, Alphagan, and Neptazane. How long will it take for the pressure to improve without medication?
Dr. Rick Wilson: If you are in the “high-bleb” phase, three to four months is average. In that phase, when the sudden flow of fluid seems to compress the tissue around the shunt plate, it takes time for the tissue to become less dense, or tiny channels to be formed across the wall.
P: I have glaucoma in my right eye. Does taking Neptazane also affect the other eye? [Neptazane is an oral carbonic anhydrase inhibitor.]
Dr. Rick Wilson: Neptazane decreases the amount of fluid the other eye makes, which may have a slightly negative effect in the eye not washing out the debris that builds up in the trabecular meshwork as well as it should. That is mostly theoretical, but seems logical. I, personally, would not take an oral medication long term for glaucoma, as the eyedrop (Azopt or Trusopt) gives close to the same effect without the systemic side effects.
P: What do you consider long-term use for oral glaucoma medication?
Dr. Rick Wilson: Longer than six to eight weeks.
P: I had a trabeculectomy, because my IOP was uncontrolled by medication. I have ICE (irido-corneal epithelial) syndrome. The surgery not only lowered my pressure, but also relieved the foggy vision caused by my swollen cornea. How did lowering the pressure help my cornea?
Dr. Rick Wilson: The cells lining the cornea on the inside have the job of pumping fluid from the corneas into the eye to keep the corneas thin and clear. In the ICE syndrome, the cells are diseased, and lowering the IOP makes it easier for them to pump the fluid out of the cornea to make it clearer.
P: How long does SLT (selective laser trabeculoplasty) lower IOP before something else must be tried?
Dr. Rick Wilson: That varies dramatically. In my experience, the older you are, the longer it works, especially if you have good color (pigment) in the drain.
P: If a patient has significant damage, can a new doctor tell on examination what pressure the patient’s optic nerve can tolerate?
Dr. Rick Wilson: It certainly helps to have the history of what the IOPs were when the damage was taking place. Otherwise, the new doctor will need to make an educated guess.
P: What percentage of glaucoma patients on medication still lose vision?
Dr. Rick Wilson: About 5% a year, but the visual-field progression may be quite slow. Visual-field progression is cause to lower the IOP significantly, usually by at least 25%, although 30 to 40% is often better.
Moderator: Thank you, Dr. Wilson. Have a safe trip to China.
Dr. Rick Wilson: Thank you and good night everyone.