Measuring intraocular pressure
The intraocular pressure should be checked regularly, as too high an intraocular pressure can constrict the optic nerve and thus damage it. In the worst case, this can lead to blindness. The measurement of the intraocular pressure is called tonometry.
There are now different procedures for this. – A very outdated and not very accurate method is the impression tonometry. Here the patient has to put his head back and the tonometer is placed directly on the cornea to measure the intraocular pressure.
Depending on how heavy the weights have to be, which lead to a flatter cornea, one can thus determine the intraocular pressure. – Also somewhat outdated, but still quite accurate by 2 mmHg, is the palpation of the closed eye with the fingers. This palpation can easily be done by the patient himself at home, once he has been shown and explained what he has to pay attention to.
There is also a self-tonometer, which works according to the same principle as an applanation tonometer. The patient is thus able to take a relatively exact measurement of the intraocular pressure from home without having to see an ophthalmologist (the necessary contact with the cornea can be compared to the insertion of a contact lens). – Applanation tonometry according to Goldmann is much more accurate.
First the eye is anaesthetized with a local anaesthetic and then a fluorescence-labelled solution is drizzled into the connective tissue sac of the skin. Now a measuring body is applied, which is attached to a spring balance. The cornea now generates a certain pressure on this measuring body.
The pressure needed to bend the measuring body is the intraocular pressure which can be read off the spring balance. This standard procedure bears almost no risk for the patient. Only in very rare cases can tiny corneal injuries or infections of the eye occur.
- In special cases, for example, when the eyes are already pre-damaged or direct contact with the cornea would not be advisable for other reasons, the intraocular pressure can also be determined using a non-contact tonometer. This works with a blast of air which flattens the cornea very slightly, so that the doctor can then calculate the intraocular pressure based on the duration and strength of the required air flow. However, this method is not the most reliable and is rarely used.
- Another way to measure intraocular pressure is Dynamic Contour Tonometry. Here, the cornea is not flattened, compared to all other methods. A certain pressure is created between the measuring head and the cornea. This pressure is the intraocular pressure. Since the measuring method is very accurate and can be repeated frequently, this is the method of choice.