Ocular tonometry is a routine eye examination that measures the pressure inside your eyes. This quick, generally painless test is a standard component of a comprehensive eye exam.
What is Ocular Tonometry
Ocular tonometry measures intraocular pressure (IOP), the fluid pressure within the eye. This pressure is maintained by aqueous humor, a clear fluid filling the anterior chamber between the cornea and iris. The aqueous humor nourishes the eye and helps maintain its shape. IOP is dictated by the balance between this fluid’s production and drainage.
Why Ocular Tonometry is Important
Measuring intraocular pressure through tonometry is important for the early detection and management of glaucoma. Glaucoma is a group of eye conditions that damage the optic nerve. Elevated IOP is a primary risk factor for this damage. Untreated high pressure can progressively harm the optic nerve, leading to irreversible vision loss. Regular tonometry allows eye care professionals to monitor IOP, identify risks, and initiate interventions to slow or prevent disease progression.
How the Test is Performed
Ocular tonometry can be performed using several methods. One common method is non-contact tonometry, often called the “air puff” test. A gentle puff of air is directed at your cornea, and the machine measures the force needed to temporarily flatten it. This method does not involve direct eye contact and typically causes a mild, momentary sensation.
Another widely used method is applanation tonometry, such as Goldmann tonometry, which is often considered a gold standard for accuracy. For this test, numbing eye drops are applied, and a small, flat-tipped probe gently touches your cornea to measure the force required to flatten a specific area. You might also encounter rebound tonometry, where a small, disposable probe gently taps the cornea, and the rebound speed is measured to determine pressure. These procedures are generally quick, lasting only a few seconds per eye.
Understanding Your Results
IOP measurements are typically expressed in millimeters of mercury (mmHg). A generally accepted normal range for intraocular pressure is between 10 and 21 mmHg. However, a single reading above this range, known as ocular hypertension, does not automatically mean you have glaucoma. It indicates an increased risk and usually prompts further evaluation.
Several factors can influence IOP readings, including the time of day, body position, and physical activity. Corneal thickness can also affect the measurement, with thicker corneas potentially yielding higher readings and thinner corneas potentially yielding lower readings than the actual pressure. Your eye care professional will consider all these factors, along with other aspects of your eye health, to interpret your tonometry results accurately and determine the appropriate course of action.