Diagnostic Tests

Eye Pressure Measurement

The measurement of internal eye pressure is very important in the diagnosis and monitoring of glaucoma cases. Measurement may be measured by 4 basic methods.

Digital Tonometry: The doctor applies light pressure on the eyeball with two fingers to examine the hardness of the eye. It is a method which requires experience but can give the opthalmologist a rough idea of the internal eye pressure.

Schiotz Tonometry (Indentation tonometry): Anaesthesia is applied to the eyes then with the patient in a supine position and looking at a point opposite, the device makes contact with the cornea under its own weight and measures the internal eye pressure. As the error rate is high, this method is not often used nowadays.

Figure 1. Applanation tonometer.

Applanation tonometry (Indentation tonometry): Measurement is made with a Goldmann tonometer, which is the most reliable  tonometer obtaining the most acccurate results and is therefore very often used. After anaesthetic drops have been applied to the eyes, measurement is made with indentation of the corneal surface by this device to which a biomicroscope is attached. Different results are given depending on the corneal thickness so it is necessary for the opthalmologist to correct the obtained result according to the corneal thickness.  

Air-puff Tonometry (Non-contact Tonometry): In air-puff tonometry there is o contact between the device and the eye.

Indentation is made with air squirted from the device on to the corneal surface and the responding air is sensed by the device and measured. It is important to have patient compliance during the measurement. Incorrectly applied measurements may give false high results.