Eye Pressure Tests - Eye Pressure

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Types of eye pressure testing.

Applanation tonometry
The Contact tonometry method uses a prism of sorts to contact the eye and apply pressure to applanate (flatten) the eye. The force needed to do this is then used to calculate the pressure. The non-contact  method uses a “air puff” to blow air into the eye causing it to flatten. Then either a pressure sensor measures the force needed to flatten the eye or in some older units the time taken from a known reference point to the time taken to applanate the eye to get a reading. A newer type the Ocular Response Analyzer also uses air but at the point of applanation, it still measures the intensity of air as the eye returns to shape and these two differences are used to calculate the pressure.

Indentation tonometry
Indentation tonometry as the name suggests indents or sinks into the eye measuring how hard or soft it is.

Rebound Tonometry
Rebound, uses a technique which bounces a probe off the eye to calculate the eye pressure by how the probe bounces and returns to the unit after hitting the eye.

Pascal Dynamic Contour Tonometer
Piezoelectric sensors embedded in the tip of the tonometer are used to measure the dynamic pulsatile fluctuations (blood flow). A prism is held onto the cornea lightly which then allows the measurements to be taken.

You could argue that rebound, Pascal Dynamic Contour Tonometer and Indentation tonometry are actually contact tonometry but because of the difference in technologies, and the contact is not as intrusive as applanation or air puff, we will loosely use this to differentiate between them.

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