Eye pressure measurement
What is eye pressure?
Eye pressure is the pressure exerted on the eyeball by a liquid called the aqueous humour located in the front part of the eye. Normal values of eye pressure range between 10 - 21 mmHg. Aqueous humour is a transparent liquid produced by the ciliary body by filtering plasma and it fills the space between the lens and the cornea. It plays a key role in delivering nutrients (amino acids, glucose, minerals, enzymes) to transparent eye structures that do not contain blood vessels (cornea, lens and vitreous).
Another important function of aqueous humour is the regulation of eye pressure, which is responsible for the tone and shape of the eyeball. In a healthy eye, there is an ideal balance between the production and release (drainage) of aqueous humour from the eye by the so-called drainage system located in the corner of the eye in front of the iris, which maintains the normal value of eye pressure.
The importance of regular eye pressure measurement
Elevated eye pressure without other symptoms or signs of the disease is called ocular hypertension. Glaucoma is a disease of the optic nerve and other nerve fibers of the retina, most often caused by increased eye pressure.
Damage to the optic nerve leads to irreversible vision loss and can lead to absolute blindness. That is why eye pressure is the main risk factor for the development of glaucoma and it is necessary to measure it at every ophthalmological examination, especially if there is a positive family history. Some patients have elevated eye pressure and vision loss and then we are talking about open or closed angle glaucoma, while others may lose vision with normal eye pressure values. This type of glaucoma is called normotensive glaucoma.
What are the methods of measuring eye pressure?
There are various methods of measuring eye pressure and we will mention the ones that are most often used in daily clinical practice:
- Goldmann's applanation tonometry is the most reliable method of measuring eye pressure where after instillation of local anesthetic, the tonometer is placed next to the surface of the cornea and corneal applanation is measured, which is then converted into mmHg.
- Portable tonometers (Perkins, Draeger, Tonopen) for measuring the eye pressure of patients in the lying position or under general anesthesia, children and patients with an irregular corneal surface. Clinical limitations of these portable tonometers are large deviations and variations in the measured values of eye pressure (+/- 4 mmHg), especially above 30 mmHg.
- Non-contact tonometry (air-puff tonometry, Pulsair) is a method of air pulse measurement that does not require contact, anesthetic or fluorescein dye. The disadvantage of this method is that it is less precise when measuring eye pressure values above 20 mmHg and the precision depends on the type of device. This type of measurement is ideal as a screening method of a healthy population.
- Pneumotonometry is a measurement method that uses an air stream directed towards the cornea - the resistance to the air flow provided by the cornea is recorded and converted into an eye pressure value. This method is a reliable way of measuring patients after refractive surgery (PRK, LASIK).
- Return tonometers (I-care) are devices that measure eye pressure without local anesthesia and with minimal possibility of infection. With the help of a thin disposable extension, it gives the average value of the eye pressure after six consecutive measurements. Due to the speed and simplicity of the measurement, it is the ideal choice for measuring eye pressure of the children.
Therapies for lowering eye pressure
Lowering the eye pressure with medication or laser therapy forms the basis of treatment with the aim of preventing further damage to the optic nerve and deterioration of the visual field, thus maintaining the independence and quality of life of such patients. Considering the degree of damage, positive family anamnesis, eye pressure level and age, the target pressure is determined for each patient.
The European Glaucoma Society recommends that everyone over the age of 40 should have their eye pressure measured at least once a year, especially if they have other risk factors.
If you have noticed changes in your vision, react promptly and book an appointment for an ophthalmological examination.