As you read in the The Basics of Glaucoma article if we were to randomly sample the eye pressures of 1000 people off the street nearly all those sampled would have a pressure under 21 mm (of mercury).
But if your pressure is greater than 21 does it mean that there is trouble ahead for you? Does it mean that you’re headed toward glaucoma? Not necessarily.
You may have what’s known as ocular hypertension.
Will you be treated?
If you have ocular hypertension you may be wondering if pressure-lowering treatment is in order. In order to assess a patient s risk for developing glaucoma we must consider all the known variables. After consideration of all these factors we can better identify the patients who are at higher risk for developing glaucoma so they can benefit from medical treatment.
Known risk factors: hard and soft
The following are the risk factors for glaucoma that we know about. Some are referred to as hard risk factors meaning that they have been shown statistically to be more significant in terms of a person eventually contracting the disease. A risk factor is referred to as being soft if it has appeared in some population studies but not statistically as significant as the hard factors.
- Age (over 60) - soft
- African heritage - hard (note in one study Hispanics had a higher incidence of glaucoma than blacks [14% versus 10%])
- Family history of glaucoma - hard
- Elevated eye pressure (above 21 mm mercury) - hard
- Optic nerve asymmetry (different size of optic nerves between the eyes as viewed by doctor) - hard
- Thin cornea (the cornea is the transparent tissue covering the front of the eye.) - hard
- Heart disease - soft
- Damage shown on visual field (provide HTML link) testing - hard
- Diastolic perfusion pressure (a relatively new risk factor)
To determine the DPP subtract the eye pressure from the diastolic blood pressure [lower number] reading. If the final number is less than 50 the risk of glaucoma is 1.7 to 6.3 times greater than the average population. - hard
Ocular hypertension: To treat or not to treat?
It wasn t that long ago that any patient with a pressure over 21 received treatment whether they had optic nerve damage or not. The rationale was that elevated pressure would most likely eventually cause problems so by taking medication future damage could be prevented or at least delayed.
Slowly this philosophy began to change and doctors started treating patients with pressure-lowering eye drops only if they had much higher pressures (typically 25 mm or greater) or they had numerous risk factors.
But none of this was based on hard science for we had no good studies to tell us when or who to treat. We knew for sure that pressure had something to do with causing glaucomatous damage. But how high was too high? This we didn t know. What really made things confusing was the fact that there existed a sub-population of glaucoma patients with lower-than-normal pressures.
So patients who had elevated eye pressures but no signs of glaucomatous damage presented doctors with a dilemma. On the one hand they could start the patient on medication to lower the pressure knowing full well that the patient might never develop a problem from the elevated pressure and would be incurring the expense and risks associated with long-term medical therapy. The other option was to closely monitor the patient for glaucomatous change before initiating therapy knowing full well that as much as 20% - 50% of the optic nerve fibers might be lost before they could make a conclusive diagnosis. There were many concerns. What if while monitoring the patient there was some acute breakthrough damage in an area of the retina that is used for reading? The patient would then be debilitated.
We now have some answers
Enter the Ocular Hypertension Treatment Study (OHTS).
In 2002 the results of the long-awaited Ocular Hypertension Treatment Study (OHTS) results were published. Doctors welcomed the results of this study because it provided a quantum leap in their understanding of ocular hypertension and the risk for developing glaucoma.
In a nutshell this large very well done study told us that by lowering the eye pressure in a patient with ocular hypertension we can delay the onset of glaucoma. In other words if we treat these people who are thought to be at higher risk for developing glaucoma we may delay or possibly prevent the disease.
At first it was easy to see that treating every patient with ocular hypertension could get messy and could result in many people being unnecessarily treated. But the OHTS study was also helpful in identifying which patients would most likely benefit from treatment.
The results were surprising and caused a lot of glaucoma experts to scratch their heads in amazement.
While race (African American heritage) and family history were expected to be strongly predictive of the development of glaucoma the statistics in the study didn t bear this out. However not unexpectedly older age and higher eye pressure were predictive of glaucoma.
The biggest surprise
The greatest commotion from this study was caused by the finding that the most predictive variable of glaucoma progression was the presence of a thin cornea. That’s right; patients with ocular hypertension who also were unlucky enough to have unusually thin corneas were about three times more likely to develop glaucoma than those with thick corneas. Hmmmm.
I m sure you re asking what does corneal thickness have to do with pressure?
Well if it makes any difference scientists are still trying to figure this one out. One theory has to do with the rigidity of a thicker cornea artificially elevating the pressure measurement and likewise a thin cornea consequently lowering the measurement of the true pressure. But experts are quick to acknowledge that there may be other unknown factors at work here.
Rarely have the conclusions of a landmark study such as the OHTS been so emphatic. Since then more and more doctors have assimilated these findings into their patient care are now measuring corneal thickness in order to accurately manage patients with ocular hypertension.
Back to you
You ve just learned that you have ocular hypertension: your eye pressures are higher than normal but there is no optic nerve damage. Certainly the OHTS study has made a good case for starting you on treatment. But as compelling as the OHTS study was and as much as it has helped us understand the nature of ocular hypertension it s important to look at this study as a whole.
Keep this in mind
There were two groups of patients in the OHTS study: one group received treatment the other group was merely observed and did not receive therapy. While it s true that significantly more people from the observation group went on to develop glaucomatous damage over a 5-year period you should also know that of the 819 people who were in the observation (no treatment) group a full 90% remained stable and did not develop damage.
It should be evident by now that starting a patient on medication for ocular hypertension is not a black and white issue. Your doctor will look at all the known risk factors as they relate to you and together you can decide if it would be best to initiate treatment or to be closely monitored.
Things can change; sometimes very rapidly. One could have normal eye pressures one year and elevated pressures only a year or two later. This is where the importance of having a routine eye examination comes into perspective particularly after age 40.
A great deal of research is now being done throughout the world to help us better understand glaucoma and ocular hypertension. Our ability to diagnosis and manage these conditions is constantly evolving.