Dr. Rajul S Parikh and Dr. Shefali R Parikh (glaucoma specialists) discuss ocular hypertension and its relationship to the development of glaucoma.
recently, we got a query by email from a 31 year old male from Pune, “I recently had an eye examination that included eye pressure test. The doctor informed me that I have high eye pressure and sent me to have a visual field test, which was normal. I can see clearly, at least from my point of view. I was told that I am a glaucoma suspect because I have ocular hypertension (high eye pressure). He wants to start me on eye drops to reduce my high eye pressure. I don’t have glaucoma, but I still have to take glaucoma medication. I can’t understand this? No one in my nuclear family has glaucoma. I have read about this 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 high eye pressure (Ocular hypertension)?
Thank you for your question.
Ocular Hypertension is defined as a sustained elevation in intraocular pressure without 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 a normal range, but this represents a minority of glaucoma cases.
Because the optic nerve is part of the central nervous system, it is composed of tissue that does not regenerate. Thus, damage or atrophy to optic nerve fibers is an irreversible event. Up to this point, you apparently do not show evidence of optic nerve damage. Technically speaking, this means that you do not have glaucoma. However, having ocular hypertension places you at risk for developing it, which makes you a glaucoma suspect.
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.
To correct for this problem, another test called pachymetry is used that measures the thickness of the cornea. This enables an ophthalmologist to interpret the applanation tonometry reading within the context of corneal thickness and provides a highly accurate measurement of intraocular pressure. However, if a pachymetry reading is not taken, an applanation tonometry test could give a result that makes it seem as though you have high eye pressure when, in fact, you do not.
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.
Our objective in answering your questions is to provide you with clear information, clear up misconceptions, and to explain about treatment options so that you can have an informed discussion with your doctor. However, under no circumstances should our response to your question be considered a substitute for ongoing consultation and examination with your doctor. Since we have not examined you, we only can speak in general terms, whereas your doctor has sufficient clinical details to evaluate your case specifically.