Tonometry
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Tonometry is an examination of intraocular pressure (IOP). Intraocular pressure depends on the balance between the production of aqueous humor (intraocular fluid) and its outflow from the eyeball.
Tonometry – in brief
- What it is: measurement of intraocular pressure – a fundamental examination in glaucoma prevention and treatment, and before any procedure
- Normal range: 10–21 mmHg in healthy individuals; pressure fluctuates throughout the day, so a single result is interpreted together with corneal thickness and optic nerve OCT
- Methods: non-contact (air puff) for screening examinations; Goldmann applanation after anesthetic drops as the gold standard
- How it is performed: a few seconds per eye, painless; after contact tonometry, do not rub your eyes for several minutes
- Price: At SwissLaser we perform it as part of a comprehensive qualification examination (400 PLN, approximately 90 minutes, Warsaw and Krakow), which includes a complete set of measurements needed before the procedure.
What is Tonometry?
Tonometry is an examination of intraocular pressure (IOP). Intraocular pressure depends on the balance between the production of aqueous humor (intraocular fluid) and its outflow from the eyeball. In healthy individuals, the normal range for intraocular pressure is generally considered to be 10–21 mmHg. Intraocular pressure fluctuates throughout the day (it is highest in the morning hours). Its average daily fluctuations do not exceed 5 mmHg. Tonometry is part of a routine ophthalmological examination.
Tonometry – an important examination before vision correction
Tonometry performed before deciding on laser vision correction aims to determine whether the procedure poses any risk to the patient. Modern non-contact tonometers measure not only corneal thickness and intraocular pressure but also the biomechanical properties of the cornea after an air impulse.
Tonometry
Methods for measuring intraocular pressure
Applanation Tonometry (Goldmann)
This method involves anesthetizing the surface of the patient’s eye while they are seated at a slit lamp. The tear film is then stained with a fluorescein solution, which fluoresces under cobalt-blue light. The tip of a prism is used to gently flatten the apex of the cornea.
Indentation Tonometry (Schiøtz)
This method involves the doctor pressing a Schiøtz tonometer against the patient’s cornea while they are lying down or have their head tilted back. The resistance of the cornea depends on the pressure within the eyeball. Measurement errors can arise from an increased corneal rigidity coefficient, which occurs in elderly individuals (falsely high pressure), or from increased corneal elasticity, which occurs in patients with significant myopia or Graves’ disease (falsely low pressure).
Non-contact Tonometry (air-puff type)
This method involves directing a puff of compressed air onto the patient’s eyeball, which flattens the cornea. The examination does not require anesthesia; the force of the puff can be surprising and unpleasant but does not cause pain.
Measurement with a handheld Tono-Pen tonometer, in which a special transducer flattens the cornea. Its advantage is that it can be used even for patients wearing contact lenses.
The most important step is to choose the appropriate method for your vision defect. During the initial consultation, we will propose the suitable laser correction technique.
Frequently asked questions
What is normal intraocular pressure?
The normal range is considered to be 10–21 mmHg. A result above 21 mmHg does not yet indicate glaucoma, but requires further diagnostics: pachymetry, optic nerve OCT, and visual field examination.
Does tonometry hurt?
No. Non-contact tonometry is a brief air puff that is merely surprising. Applanation tonometry is performed after anesthetic drops and lasts a few seconds.
How often should intraocular pressure be checked?
Individuals over 40 years of age – every 1–2 years, more frequently if there is a family history of glaucoma, diabetes, high myopia, or chronic steroid use. Before any ophthalmic procedure, tonometry is mandatory.
Why does the tonometry result depend on corneal thickness?
A thick cornea offers greater resistance and inflates the measurement; a thin one underestimates it. That is why we always assess pressure together with pachymetry – as we do in our qualification examination.
How much does an intraocular pressure examination cost?
At SwissLaser, tonometry is included in the comprehensive qualification examination for 400 PLN, performed in Warsaw and Krakow.
We perform all examinations in Warsaw (Kolejowa 1) and Krakow (Kluczborska 15/U3). Diagnostic overview: eye examinations; what happens next: qualification for the procedure.
