Tonometry: Measuring Eye Pressure and Detecting Glaucoma
Tonometry is a diagnostic procedure used to measure intraocular pressure (IOP). It is a key tool for the early detection and monitoring of glaucoma.
Things worth knowing about "Tonometry"
Tonometry is a diagnostic procedure used to measure intraocular pressure (IOP). It is a key tool for the early detection and monitoring of glaucoma.
What is Tonometry?
Tonometry is a medical examination procedure used to measure intraocular pressure (IOP) -- the pressure inside the eye. This pressure is maintained by the aqueous humor, a fluid that is continuously produced and drained within the eye. Elevated intraocular pressure is one of the most important risk factors for developing glaucoma, a serious eye condition that can lead to irreversible vision loss if left untreated. Tonometry is therefore a central tool in ophthalmological screening and diagnostics.
Principles and Methods
There are several types of tonometry, each based on different physical principles:
Applanation Tonometry (Goldmann Tonometry)
Goldmann applanation tonometry is considered the gold standard for measuring intraocular pressure. After the eye is numbed with anesthetic eye drops, a small probe is gently placed against the cornea. The pressure required to flatten a defined area of the cornea is measured and corresponds to the intraocular pressure.
Non-Contact Tonometry (Air Puff Tonometry)
Non-contact tonometry uses a brief puff of air directed at the cornea. The deformation of the cornea is measured optically, and the intraocular pressure is calculated from this data. Since this method does not require direct contact or anesthetic drops, it is widely used in routine screening at eye clinics.
Rebound Tonometry
Rebound tonometry uses a tiny probe that momentarily touches the cornea and bounces back. The speed of the rebound is used to calculate intraocular pressure. This method is particularly suitable for use in children and for home monitoring by glaucoma patients.
Indentation Tonometry (Schiotz Tonometry)
Indentation tonometry is an older technique in which a weighted plunger is placed on the cornea. The depth of indentation reflects the intraocular pressure. This method is rarely used today but may still be encountered in certain clinical settings.
When is Tonometry Used?
Tonometry is indicated in a variety of clinical situations:
- Glaucoma screening as part of routine eye examinations
- Monitoring of patients with known glaucoma or elevated IOP (ocular hypertension)
- Before and after eye surgery, especially following laser vision correction procedures such as LASIK or PRK
- In cases of suspected acute angle-closure glaucoma, a medical emergency characterized by sudden severe eye pain, redness, and vision loss
- During long-term corticosteroid therapy, as these medications can raise intraocular pressure
Normal Values and Clinical Significance
The normal range for intraocular pressure is generally between 10 and 21 mmHg. Values above 21 mmHg are considered elevated (ocular hypertension) and represent a risk factor for glaucoma. However, it is important to note that glaucoma can also develop at normal IOP levels (normal-tension glaucoma), and not everyone with elevated IOP will necessarily develop glaucoma. Therefore, tonometry results must always be interpreted alongside other examinations, such as visual field testing and optic nerve head assessment.
What to Expect During the Examination
Tonometry is generally a quick and minimally uncomfortable procedure. For contact-based methods, anesthetic eye drops are applied beforehand, and a dye called fluorescein may be used to enhance measurement accuracy. The procedure typically takes only a few minutes. Patients who wear contact lenses should remove them before the test.
Limitations and Influencing Factors
The accuracy of tonometry can be affected by several factors. Corneal thickness is one of the most significant -- thinner corneas tend to produce lower readings, while thicker corneas may result in higher readings than the actual IOP. Corneal curvature and previous refractive surgery can also influence measurements. For this reason, corneal thickness (pachymetry) is often measured alongside tonometry to allow for accurate interpretation of IOP readings in glaucoma diagnostics.
References
- European Glaucoma Society (EGS): Terminology and Guidelines for Glaucoma, 5th Edition, 2020. Available at: https://www.eugs.org
- Kniestedt C., Punjabi O., Lin S., Stamper R.L.: Tonometry through the ages. Survey of Ophthalmology, 2008; 53(6):568-591. PubMed PMID: 18929764.
- American Academy of Ophthalmology (AAO): Glaucoma - Preferred Practice Pattern, 2022. Available at: https://www.aao.org
Most purchased products
For your iron balance
Specially formulated for your iron balance with plant-based curry leaf iron, Lactoferrin CLN®, and natural Vitamin C from rose hips.
For your universal protection
As one of the most valuable proteins in the body, lactoferrin is a natural component of the immune system.
For Healthy Oral Flora & Dental Care
Formulated lozenges with Dentalac®, lactic acid bacteria, and Lactoferrin CLN®The latest entries
3 Posts in this encyclopedia categorySI Joint Blockage
Most read entries
3 Posts in this encyclopedia categoryMagnesiumcarbonat
Calorie content
Cologne list
Related search terms: Tonometry