What Is The Intraocular Pressure?
Most of us have been to the ophthalmologist or optometrist and have had our eye pressures measured. This process is called tonometry. However, most of us have no idea what our eye pressure is. It's not because we aren't interested (I have scores of patients who can tell me their last blood pressure). The main reason that patients don't know their eye pressure is because the doctor never tells them! Doctors tend not to tell their patients things because, A; they think the patient won't understand what they are talking about and B; it takes too much time to explain it to them.
Since elevated eye pressure is the leading component of glaucoma, a blinding eye disease, it is important to know and understand our eye pressure.
The fluid within our eyes is under a certain amount of pressure. This pressure helps the eye to keep its spherical shape so we maintain stable vision. This pressure is called the intraocular pressure (IOP). Just as barometric pressure is measured in millimeters of mercury (mm Hg), so is the pressure within the eye. The normal eye pressure falls within the range of eight to twenty one mm Hg, with the average being sixteen.
The most common way of determining the IOP is a test called pneumotonometry. Also known as the "puff of air", the pneumotonometer blows a brief burst of air at the eye to measure the IOP. Although the test is a bit startling, it is harmless. The results are not as accurate as some of the other methods of measuring IOP. However, the test is useful as a screening procedure for glaucoma. If the pneumotonometer measures an elevated pressure, then further evaluation with a more accurate tonometer is necessary.
Goldmann tonometry is the most accurate method of measuring the IOP. This test first involves placing an anesthetic drop containing a fluorescent green dye into the eye. Once the eye is numb, a small clear cylinder of smooth plastic (the tonometer tip) is placed in contact with the surface of the eye. The doctor then looks through the microscope at the tip and adjusts the tonometer to determine the pressure. This adjustment is usually done under blue light illumination, which makes the fluorescent green dye glow. The blue light is the part of the test that most patients remember.
Once the pressure is measured, your next question should be, "what is my eye pressure, doc?" Don't accept "normal" or "fine" as an answer. Ask the actual value and remember it. This information may be very useful if, in the future, there is any suspicion of glaucoma. Don't hesitate to ask your doctor to explain your eye pressure. If he or she can't take the time to answer questions about your eye exam, then you need a new ophthalmologist.
