What is non-contact tonometry?
Non-contact tonometry test helps diagnose glaucoma. The doctor will use a tool called a tonometer that blows a small puff of air, measuring the pressure in the eye indirectly by the resistance of the eye to the puff. Flattening instruments can also measure pressure. They are the most accurate, but you will need local anaesthesia.
Non-contact tonometry principle
Non-contact tonometry (NCT) is the most recently available technology for the clinical measurement of intraocular pressure (IOP). This technique was originally conceived’ in 1951 by Erich Zeiss.
A blast of air creates a constant force, momentarily deforming the cornea. It is difficult to determine the exact nature of the corneal deformation, although the central cornea is postulated to be flattened at the time the pressure measurement is made.
Types of NCT
- Table mount – Expert NCT
- Handheld – Keeler Pulsar Tonometer.
Uses of non-contact tonometry
- Without pollution
- No possibility of corneal abrasion
- No reactions to topical anaesthetics
- Value in mass screening and studies of new anti-glaucoma drugs.
Caution in non-contact tonometry
There have been reports of subepithelial air bubbles after repeated use of NCT. NCT is a safe and reliable method to measure IOP. Caution should be exercised when measuring glaucomatous eyes, as a lower pressure in IOP above the normal range can be recorded as in abnormal corneas.
What happens during a non-contact tonometry test?
Before the test, your eye doctor will put numbing eye drops in your eye so that you don’t feel anything touching it.
Once your eye is numb, your doctor may touch a small strip of paper that contains orange dye to the surface of your eye to stain it. This helps increase the accuracy of the test.
Your doctor will then put a machine called a “slit-lamp” in front of you. They’ll ask you to rest your chin and forehead on the supports provided, then move the lamp toward your eye until the tip of the tonometer probe touches your cornea.
By flattening your cornea just a bit, the tonometer can detect the pressure in your eye. Your eye doctor will adjust the tension until they get a proper reading. Because your eye is numb, you’ll feel no pain during this procedure.
Tonometry is extremely safe. However, there’s a very small risk that your cornea could be scratched when the tonometer touches your eye. However, even if this happens, your eye will normally heal itself within a few days.