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.
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 thing is to choose the right method for your vision defect. During initial consultations, we will propose the appropriate laser correction technique.
