Eye Didn't Know!

Glaucoma Linked to Low Pressure in Brain?

Did you know? A study published in the May 2008 journal Ophthalmology found a fascinating link, which, if verified, could alter how we think of glaucoma. The Mayo Clinic studied the records of all patients who had lumbar punctures (spinal taps) between 1996 and 2007. They identified 28 of these patients as having glaucoma, and compared them to 49 patients who did not.

During a lumbar puncture, the pressure within the spinal column (which connects to the brain) is measured. The spinal pressure in the glaucoma patients averaged 9 mm Hg, and the controls measured 13 mm Hg. Since the average eye pressure is between 10 and 21, (often higher in glaucoma) that means that the pressure gradient between the eye and the brain could be higher in the glaucoma patients. This would damage the optic nerve, which is seen in glaucoma.

Did you also know? The only accepted treatment we have now for glaucoma involves lowering eye pressure, with eyedrops, laser, or surgery.

Are we due for a new class of glaucoma medications?

Did you know? It has been twelve years since there have been any significant additions to our supply of medications for glaucoma. In 1996 Xalatan was introduced, the first of the prostaglandin agents which quickly took over first-line therapy for most glaucoma patients. The prostaglandins simply worked better with fewer side effects than the other medications available.

A new class of medication may be on the horizon. Rho-kinase inhibitors, (ROCK-inhibitors) are molecules which relax smooth muscle, a muscle which is found, among other places, in the drainage system within the eye.

When this drain does not work properly, the pressure within the eye rises, which can lead to damage to the optic nerve within the eye. When this happens, vision can be lost, and we call it glaucoma. Relaxing the mesh-like tissue within this drain can apparently cause pressure to be lowered.

Several pharmaceutical companies are looking into these molecules. Studies in monkeys have shown a larger pressure lowering effect than Xalatan!

Will these studies result in a new class of glaucoma medications? Only time will tell. Ophthalmologists and glaucoma patients could benefit from a new arrow in our quiver!

More information can be found here.

Did you also know? Statin drugs (lipid-lowering agents) such as Lipitor, Zocor and Crestor are also ROCK-inhibitors.

Measuring Eye Pressure

Did you know? Until 1905 there was no objective way to measure pressure within the eye. In that year, Norwegian ophthalmologist Hjalmar Schiotz invented the first tonometer, which now bears his name, the Schiotz tonometer.

Until this time, doctors estimated pressure within the eye by pushing on the eye through the eyelid, and guessing, much like you might push on a bicycle tire with your thumb and guess the pressure. The Schiotz tonometer actually works in much the same way, it measures the weight necessary to indent the cornea a standard amount.

Knowing the pressure more accurately allows us to better diagnose and treat glaucoma, a disease usually caused by elevated eye pressure damaging the optic nerve.

The Schiotz tonometer is still used in many parts of the world, and when I trained, it was what most doctors used as a portable tonometer.

Did you also know? Dr. Schiotz was also responsible for introducing the concept of sterilizing surgical instruments (by boiling) to Norway.

Steroid for Glaucoma?

Did you know? It may be possible to lower eye pressure in glaucoma with injections of a steroid called anecortave acetate. Although most steroids have to potential to raise eye pressure, this steroid has been shown in a number of studies to lower eye pressure. Researchers at Johns Hopkins, in Baltimore, injected a small amount of medicine or placebo just under the surface of the eye in 85 patients. After three months, the patients receiving the medicine had a pressure reduction of 7.4 mm Hg compared with 1.4 mm Hg in the placebo group. Read more here.

Did you also know? Many patients have enormous difficulty taking their glaucoma eyedrops properly. If it becomes possible to control eye pressure with a painless injection under the eye every three, six, or twelve months, that would give us a very important additional measure to preserve vision in glaucoma.

Alternative Therapies for Glaucoma?

Did you know? It is said that 50% of patients with glaucoma use "alternative" therapies, that is, therapies other than those prescribed by their physician. The rate may be higher in Asian populations. The question is, do they work??? A prominent glaucoma specialist from San Francisco, John Hetherington, M.D., recently reviewed the literature on the subject. He reached the following conclusions:

Vitamins A, B1, B12, C, and E, as well as antioxidant supplements, had no meaningful effect on intraocular pressure or glaucoma progression.

Marijuana decreases eye pressure, but its effects are very short–lived with significant side–effects. Topical application of its components (there are over 400!) has not yet shown to be effective, but is being studied.

Ginkgo biloba increases ocular blood flow and thus may protect the optic nerve. Dr. Robert Ritch is a specialist who has advocated gingko use for glaucoma for many years. Gingko may cause side effects such as bleeding, especially when used with aspirin, so should be used with caution or after consultation with a primary care physician.

There is no evidence that bilberry is beneficial for glaucoma or optic nerve health.

Drinking excess water can raise eye pressure temporarily.

Alcohol can decrease eye pressure temporarily, but obvious toxicity can result with excess!

Meditation produces insignificant reduction in eye pressure.

Acupuncture has not be shown to affect eye pressure.

Exercise has a significant eye pressure lowering effect over time.

In summary, exercise and possibly gingko are the only alternative therapies which currently may be effective in glaucoma. So save your money and keep walking!

Did you also know? Yoga exercises which feature inversion for long periods of time should definitely be avoided in glaucoma, as they can increase eye pressure greatly!

(photo by Joseph Renger, wikimedia commons)

You want to take my temperature where?

Did you know? A recent study published in the British Journal of Ophthalmology demonstrated that the temperature of the surface of the eye correlated with the blood flow in the back of the eye. It is believed that decreased blood flow to the optic nerve may be a risk factor for developing glaucoma, so a decreased surface temperature may indicate poor blood flow, which may be a risk factor for glaucoma.

Did you also know? In the past five years most ophthalmologists have routinely started to measure corneal thickness in glaucoma suspects, as thin corneas have been shown to increase one's risk for glaucoma. (we are not sure why!)

The ultimate eye pressure gauge

Did you know? Researchers in Germany say they have developed a sensor which can be integrated into an intraocular lens to continuously monitor the pressure within the eye.

Patients with glaucoma suffer damage to the optic nerve and possible vision loss when the pressure exceeds a safe level. The standard of care today is to check the eye pressure at the ophthalmologist's office, which might occur once every three, six, or twelve months. This obviously does not give a complete picture of the eye pressure within the eye.

Most patients with glaucoma eventually need cataract surgery. A lens implant containing a sensor to continuously monitor pressure, transmitting it to an external receiver, would provide us with a wealth of information.

This device is in trials and could be available within three years. Read more here.

Did you also know?
A similar device could be implanted in a major artery to continously monitor blood pressure!

A safer beta-blocker?

Did you know? I previously wrote about Othera Pharmaceuticals, which is attempting to develop an eyedrop to prevent cataracts. The same company is investigating a beta-blocker eyedrop which may have no systemic side-effects. The compound is designed to be active in ocular tissues, but rapidly inactivated in the bloodstream.

Did you also know? Beta blockers, such as Timoptic and Betagan, are very effective in lowering eye pressure in patients with glaucoma. Possible side-effects include a slowed heart rate, asthma, and depression.

Corneal thickness and glaucoma

Did you know? The thickness of the cornea (the clear window in the front of the eye) has a direct influence on the measurement of pressure in the eye. With current technology, a thin cornea will lead to a falsely low pressure reading, while a thick cornea will lead to a falsely high reading. This can cause errors in the diagnosis and treatment of glaucoma, which occurs when the eye pressure is too high for the health of the optic nerve. For this reason, I now measure corneal thickness in all patients who are suspects for glaucoma. I often find patients treated unnecessarily for glaucoma, as well as patients with thin corneas who actually need treatment.

Did you also know? A Canadian company is developing a device which uses the reflectance of sound waves off the eye to measure eye pressure. Time will tell if it will replace current methods of measuring eye pressure.

Glaucoma Awareness Month

Did you know? January is Glaucoma Awareness Month. The American Academy of Ophthalmology has a patient handout describing glaucoma in a nutshell. In short, glaucoma is a disease of the optic nerve (the nerve that transmits messages from the eye to the brain). The main risk for glaucoma is high pressure in the eye, but there are other risk factors, such as age, black race, family history, and others.

Did you also know? There are NO symptoms of early glaucoma. If you have symptoms (vision loss, halos around lights, etc.) the disease is VERY advanced. Regular checkups by your ophthalmologist can detect glaucoma early and minimize the risk of vision loss.

Mifepristone glaucoma trials

Did you know? Mifepristone, also known as RU-486, or Mifeprex, is the pill used to terminate pregnancy. It works by blocking the effects of steroids, such as progesterone, which is necessary in the uterus during pregnancy. There is a new clinical trial studying this compound, as an eyedrop, to evaluate its potential in treating steroid-associated glaucoma. Steroids are used to treat inflammation in the eye, but are sometimes limited by the side-effect of raised eye pressure. It would be a huge advance to be able to prevent steroid-induced-glaucoma with this compound.

Did you also know? The use of steroid therapy in the eye is growing. Steroids are now being injected into the eye to treat diabetic macular edema, a common cause of visual loss in diabetics, and are also being tried in macular degeneration. The company sponsoring this clinical trial, pSivida, also manufactures a steroid implant used for diabetic eye disease.

Nocturnal Eye Pressure

Did you know? High pressure within the eyes is the major risk factor for glaucoma. During the past few years, researchers at UC San Diego have studied how eye pressure varies during the day and night. They enlist volunteers to spend the day and night in a sleep center and measure their eye pressure at intervals. Among their findings is that peak eye pressure tends to occur just before awakening in the early morning. This is important because eye pressure measured in the office setting may not reflect the peak eye pressure which may be damaging the optic nerve.

Did you also know? Companies around the world are working on a device which would allow patients to easily monitor eye pressure at home, as they can do with blood pressure or blood sugar. So far, none have succeeded!