Whats new in eye pressure readings for glaucoma? For years the fluid pressure in your eyes has been largely measured by two different methods. The first method applies pressure to a small area of the clear tissue on the front of the eye know as the cornea. This method requires a drop to make your eyes numb for five to then minutes so the small tip of the instrument can lightly touch the front of your eye without having discomfort or a blink reflex. You may remember looking at small blue light approaching your eye. This is used with an orange dye to help it glow, and makes it easier for the eye doctor to align the half circle patterns that determine the final readings. The second method sends a small puff of air to the front of your eye to flatten the tissue. It then acts like a mirror and reflects an infrared light beam back into the instrument. The amount of time it takes for this to happen is correlated with the pressure in the eye and it gives a digital readout.
Both methods are good indicators of the actual eye pressure but not perfect. They base their readings on an average thickness of the cornea, a little more than half of a millimeter. Tissues that are thinner than average offer less resistance to any pressure applied and give readings lower than the actual pressure. The true pressure could only be determined by a method involving poking a hole in your eye which is obviously something only done on people not breathing or part of this world. Everyone else seems to complain about such a technique. Since there is less resistance from a thinner tissue the eye pressure readings are artificially low.
Eye pressures average 15-16 and the normal range is about 6 to 20. If they are 21 or higher your optometrist starts to be concerned you may have glaucoma, a disease where elevated eye pressure contributes to eye sight loss and blindness if not treated in a timely manner. The cornea also has structural factors that determine how well it rebounds after pressure is applied. Tissues that don’t rebound as well also read artificially low pressures.
The last few years have seen more instruments used to measure the thickness of the cornea and factor this in as an approximate amount to add or subtract form the eye pressure readings. A new generation of instruments are being developed to compensate for these aberrations to the pressure readings. One instrument takes a hundred reading in a second and averages them into one number to improve accuracy. The tip of this instrument dynamically adjusts its shape to match the curvature of the cornea and help eliminate the structural effects on pressure readings by applying force uniformly. A second instrument measures how long it takes the tissue to rebound and recover its curvature after the air puff flattens it. This is factored into the final pressure reading.
Your eye pressure is dynamic, not static and does change some throughout the day. Some people have larger swings so the eye pressure is frequently read at different times of the day so you eye doctor is looking at a daily range of pressure instead of a single reading. Eye pressure is only one of the determining issues in deciding if you have glaucoma, but it is an important one. The future holds great promise for finding improved ways to determine your eye pressure with more accuracy and the other contributing factors that cause it to vary.