Eye Pressure Test (Tonometry)
Tonometry is a routine procedure that tests your eye pressure during routine eye exams. Either an optometrist or an ophthalmologist can perform the exam. The test is done to ensure the health of your eyes, since elevated eye pressure can lead to eye diseases such as glaucoma and even blindness.
The tonometry test can identify abnormally high intraocular pressure or IOP. Normal IOP readings are between 12 and 20 millimeters of mercury (mmHg). An intraocular pressure higher than 20 mmHg can lead to or be an indication of existing glaucoma. Untreated glaucoma can lead to blindness.
Part of Routine Precautions
Tonometry tests should be part of any routine eye exam for an adult. The American Optometric Association guidelines suggest healthy people between the ages of 18 and 50 undergo an eye exam a minimum of once every two years. After the age of 50, you should have an eye exam every year unless there is a reason not to do so. The eye pressure test may be delayed if there has been an injury to your eye or if you have an ulcer on your cornea.
While every child should receive a complete eye exam before the age of two, a tonometry test is not usually performed on children unless surgery had been performed to correct a cataract. For children older than three, every two to five years is acceptable for a test, as long as there’s no hereditary history of eye problems. Eye exams should take place every year, however, for children with a family history of eye diseases.
Preparation for a Tonometry Test
Generally, you don’t need to make any special preparations for an eye pressure test. Your contact lenses must be removed before the test, so it’s recommended that you either wear eyeglasses to the appointment or at least have them handy. To achieve accurate readings, it’s suggested that you not wear anything tight around your neck, such as a snug turtleneck sweater or a choker. You also need to be as relaxed as possible. Strenuous exercise and caffeine consumption are also discouraged before the exam.
Tell your eye doctor about any prior eye injuries you’ve had. Your doctor administers eye drops prior to the exam, which should numb your eyes for about 10 to 30 minutes. Not only do the eye drops function as an anesthetic, but they also possess a yellow die that glows in blue light. So make sure your doctor knows if you have any allergic reactions to eye drops or if your family has a history of glaucoma.
The Tonometry Procedure
The tonometry test is administered using a tonometer. This device measures the intraocular pressure created by the fluid inside your eye in mmHg. There are various types of tonometers. Some touch your iris directly, while others only make contact with your eyelid. Still others don’t make any contact with your eye whatsoever. The most common type of test involves direct contact of the tool with your eyeball, and this requires that your eyes be numbed with drops. The tools available for this procedure include:
- Tono-Pen/Accu-Pen: This handheld device uses a one-tap, one-reading gravity offset technology.
- PASCAL Dynamic Contour Tonometer (DCT): This instrument uses the technique of contour matching, as opposed to the traditional applanation or touching the iris directly.
- Goldman: This tool is still considered the industry standard. It’s a table-mounted instrument that uses applanation, and the resistance from the iris is the measured result.
- Icare: This device can be used at home so that you can perform daily eye pressure tests.
- Schiötz: This is generally considered a preliminary testing method, and it should be verified by applanation if the reading is high. It functions by indenting the eye with a weighted plunger and then measuring the kickback on the scale.
- The Diaton Tonometer: Another tonometry handheld tool, it can perform eye pressure tests through the surface of the eyelid. It’s considered an effective measurement device without the need for the numbing eye drops.
An Ocular Response Analyzer® (ORA) is the only tool in tonometry that functions without any contact with your eye. It measures corneal hysteresis (CH), which has been shown to be a reliable indicator of glaucoma progression. CH indicates the biomechanical properties of your cornea that differ in thickness or topography. In other words, it surveys the geometry of your eye.
The accuracy of your tonometry test result can be disrupted by many extraneous factors. For example, the surface thickness can be different from one cornea to the next, so even if you have a harder cornea and an eye pressure test with high IOP results, you still may have healthy eyes. Illness, caffeine, eye irritation, and strenuous physical activity also can alter an IOP reading. Your ophthalmologist may require a second reading if you have a high IOP that can be explained by these factors.
Risks of Tonometry
Eye pressure tests are considered to be extremely safe procedures; however, there are some minor risks involved. If you undergo one of the tonometry tests requiring contact with your eye, there is a risk of scratching your lens. Any scratch on your cornea may be both uncomfortable and painful, but it’s common for these types of injuries to heal in a matter of days.
Some people find the eye drops used to anesthetize the eyes prior to using the instrument to be unpleasant, but they’re not dangerous unless they trigger an allergic reaction. In rare circumstances, the contact of the equipment itself on your eye can lead to infections.
A complete eye exam should take a little more than an hour, but the tonometry test during that full exam lasts no longer than one minute once everything is set up. It’s a vital part of your routine exam, however, because elevated IOP is a natural precursor to glaucoma. Since there are no symptoms associated with that disease, your eye pressure test is the best-known way of detecting its development.
It’s also important to record your history of these tests to see if there has been an increase in eye pressure. Untreated, glaucoma can lead to blindness. This is unnecessary since it’s preventable. There are medications available to control excessive eye pressure, and your eye doctor can prescribe them for you.
Important Reminder: This information is only intended to provide guidance, not a definitive medical advice. Please consult eye doctor about your specific condition. Only a trained, experienced board certified eye doctor can determine an accurate diagnosis and proper treatment.
Do you have any questions about Eye Pressure Test (Tonometry) procedure in NYC? Would like to schedule an appointment with New York Ophthalmologist or Optometrist, Dr. Saba Khodadadian of Manhattan Eye Specialists, please contact our office for consultation with NYC Eye doctor.
Dr. Saba Khodadadian, Optometrist (NYC Eye Doctor)
New York, NY 10010
(Between Madison Ave & Park Ave)
☎ (212) 533-4821