Ocular Hypertension Treatment Study
Chat Highlights
June 4, 2008

On Wednesday, June 4, 2008, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Ocular Hypertension Treatment Study".

Moderator: Tonight's topic is a very interesting one, The Ocular Hypertension Treatment Study. Would you like to introduce it, Dr. Pro?

Dr. Pro:  I'd be happy to. Let's just call it OHTS to shorten the typing.

The OHTS was one of four recent important studies in glaucoma. The others I have mentioned previously, such as the Advanced Glaucoma Intervention Study (AGIS), the Collaborative Normal-Tension Glaucoma Study (CNTGS), the Early manifest Glaucoma Trial (EMGT), and the Collaborative Initial Glaucoma Treatment Study (CIGTS). I guess that is five studies, although some are referred to less than others.

I may be biased but current glaucoma thought and treatment may be most influenced by the results of AGIS and OHTS.

Moderator: Why is the OHTS considered so important?

Dr. Pro:  Well, allow me to first describe its design and then get to the results.

Design: It compared the effect of a stepped regimen of medication versus observation in persons with Ocular Hypertension (OHTN). The outcomes measured were the onset of visual field loss and/or optic nerve damage; the development of Primary Open Angle Glaucoma (POAG).

Patients in the study: IOP between 24 to 32 mmHg in the study eye, normal visual fields, and normal optic nerves. Patients were randomly assigned to medication or observation. Treatment: Topical anti-glaucoma drops with a target reduction of 20% or an IOP of 18 mmHg or less.

Findings: The treatment group had an IOP reduction of 22.5% vs. 4.0% in the observation group. The probability of progression in the treatment group was 4.4%. In the observation group it was 9.5%. Risk factors identified were: older age; higher baseline IOP; thin central corneas; visual field characteristics; and optic nerve appearance.

In this group of patients, treated patients had half the risk as untreated patients to develop POAG.

Some questions or more from me?

P:  Who conducted the study?

Dr. Pro:  Well, this study was a large multi-center trial. The lead researcher was Michael Kass. It was NIH (National Institutes of Health) funded.

As is the case with many studies, the most relevant finding to today’s glaucoma management was not part of the original design. I think it now seems clear that ocular hypertensives with certain risk factors should be treated, and OHTS helped to clarify that. But the fact that thin corneas are a risk factor was completely unknown before this, and measurement of corneas was not even part of the original design of the study.

P:  Dr. Pro, if only 10% of the untreated group converted from ocular hypertension to glaucoma, doesn't that mean that 90% of the treated group did not need to be treated?

Dr. Pro:  Of course, but that can mean significant optic nerve damage to those 10% that develop glaucoma, which can cost society millions of dollars. In terms of glaucoma treatment, there have been some recent articles on its cost effectiveness because glaucoma therapy is chronic and expensive.

It may be more cost effective to prevent glaucoma with the additional costs of medications and lost productivity in that extra 5% than to observe them, but I don't practice medicine with those facts in mind; rather, I think of the individual in front of me and what risk that person has to develop glaucoma.

P:  How do you weigh the risk factors to determine which patients should be treated earlier rather than later?

Dr. Pro:  Well, I mentioned the five risk factors above. In fact, the researchers did put together a risk calculator. It looks like a regular calculator and you can input patient's data and it spits out the percentage risk that the person would develop POAG.

A few caveats—it works only for patients who are like those in the study, with age and IOP in the study range. Also, it does not take into account some difficult to measure features. For example, some individuals who would seem to be at risk never develop POAG, and remain suspects their whole lives. One would presume that at some point their true risk should be adjusted downward, but the calculator is incapable of these clinical nuances.

P:  Dr., I know there were a number of articles published right when the study came out. Is the data is being "mined" and are there still articles coming out?

Dr. Pro:  I would think so. I guess the most recent work was merging the results of OHTS with a European study of similar design. Also one of the troubling early OHTS findings was that diabetes is protective against POAG. It made no sense and has been debunked in newer publications.

P:  What is your experience of doctors being willing to adjust treatment based on study findings?

Dr. Pro:  I think they should be open to study findings. That is not to say that the studies are perfect. In fact there remain many different approaches to glaucoma, and some of this is due to the weaknesses in the studies, such as smaller sample sizes, but the recent studies have certainly changed opinions, such as the importance of getting the IOP quite low in certain patients.

Moderator: Thanks for your time and knowledge, once again.

Dr. Pro:  You are welcome and good night all!

On June 18, Dr. Pro discussed "Glaucoma and Obesity" in the Chat room. Click here for highlights of that meeting.

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