OCULAR HYPERTENSION

Ophthalmologist Carolina Valdivia, MD discusses ocular hypertension and its relationship to the development of glaucoma.

Dear Dr. Valdivia,

I recently had an eye examination that included a test with a Goldmann instrument. I'm sure about this because I saw the name on the machine. The doctor informed me that I have high eye pressure and sent me to have a visual field test. The results were inconclusive, so he ordered a second visual field test, which was normal.

I never have had to use eye glasses. I can see clearly, at least from my point of view. The good news is that the doctor told me that I do not have glaucoma. Instead, he said that I am a glaucoma suspect because I have ocular hypertension. He wants to start me on eye drops to reduce my high eye pressure. Huh? I don't have glaucoma, but I still have to take glaucoma medication anyway?

I am African-American and I heard somewhere that this makes me at risk for glaucoma. However, this whole thing seems strange, since no one in my nuclear family has glaucoma. I have read on your website about glaucoma diagnosis, but I still am confused. If I don't have glaucoma and my visual field test is normal, why do I have to take glaucoma medication for my ocular hypertension?



Thank you for your question and for your trust in glaucoma-eye-info.com.

Ocular Hypertension is defined as a sustained elevation in intraocular pressure without detectable damage to the optic nerve or changes in the visual field. The high eye pressure has no apparent cause.

Conversely, glaucoma is defined as the presence of optic nerve and/or visual field damage. The damage is associated with high eye pressure in 80 to 90% of cases. There is a type of glaucoma called normal tension glaucoma in which optic nerve and/or visual field damage occurs despite intraocular pressure being in the statistically normal range, but this represents a minority of glaucoma cases.

There is a test called optical coherence tomography (OCT) that can detect small changes in the optic nerve, even before these changes have an effect on optic nerve function (as measured by a visual field evaluation ). OCT can be very useful for tracking people with ocular hypertension.

In your question, you did not mention what your most recent intraocular pressure readings were. It is important that you have an accurate reading. The test that you were given used a Goldmann Applanation Tonometer, which is considered the gold standard for measuring intraocular pressure. However, it has a small drawback.

Applanation tonometry works by gently touching the tonometer tip to the cornea of the eye. A measurement is then taken that represents the resistance to indentation of the cornea by the tip. If pressure inside the eye is high, the resistance also will be high.

All measuring instruments can give false positive or false negative readings. In the case of applanation tonometry, corneal thickness can affect the measurement. For example, an eye with a thick cornea will be more resistant to indentation, irrespective of the pressure inside the eye. This can give a false positive reading, in which intraocular pressure appears to higher than it actually is. To illustrate, a person with a thick cornea may have an actual eye pressure of 16 mmHg, but the tonometer may give a reading of 20 mmHg. The opposite occurs in eyes with thin corneas. The tonometer tip encounters less indentation resistance and therefore gives a false negative reading that is less than the actual intraocular pressure.

Assuming that your ocular hypertension diagnosis is accurate, scientific studies have been conducted that can provide a general picture of how ocular hypertension behaves over time. It should come as no surprise that the higher the level of intraocular pressure, the greater chance of developing glaucoma. For example, persons with high eye pressure at 25 mmHg or above are more likely to develop glaucoma after 5 years compared to those with 24 mmHg or less.

Of course, some people with ocular hypertension never develop glaucoma. However, it would be unwise for anyone to assume that they will be one of these individuals, as medical science has no reliable way of predicting who will or will not develop glaucoma. For this reason, all persons with high eye pressure must be followed regularly by an ophthalmologist to assess for optic nerve damage. As I mentioned earlier, this typically is accomplished through optical coherence tomography (OCT).

I understand that it seems counter-intuitive that your ophthalmologist is going to start you on anti-glaucoma medication when, in fact, you do not have glaucoma. However, there are several reasons why your ophthalmologist may have made this decision. Prominent among these is that you have two major risk factors for glaucoma: ocular hypertension and African-American ethnicity. But the only way for you to gain an complete understanding of the rationale behind this decision is to ask your ophthalmologist directly. I strongly recommend that you do this. I am confident that he or she will be able to explain why it is important for you to take medicine to reduce your high eye pressure.

Carolina Valdivia, MD

REFERENCE:

Allen MY and Higginbotham EJ. Primary Open-Angle Glaucoma. In: Morrison JC and Pollack IP. Glaucoma: Science and Practice. New York: Thieme, 2003:153-162.

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