Glaucoma is a leading cause of irreversible blindness worldwide, and raised intraocular pressure (IOP) is a major risk factor for this condition. IOP measurement is a fundamental tool in patients with ocular hypertension or glaucoma, and there are several types of tonometers commonly used in clinical practice.

1. Applanation Tonometry

1. 1. The Goldmann tonometer is the gold standard for IOP measurement, as it provides high accuracy and reproducibility. This method involves measuring the force required to flatten a small area of the cornea, and the IOP reading is determined by this measurement. However, the use of topical anesthetic drops is necessary, and improper disinfection of the tonometer can pose a risk of infection.

1. 1. Keeler AccuPen is a handheld tonometer that uses applanation tonometry to measure IOP. It is a portable device that uses a probe with a small flat tip to measure the force required to flatten a small area of the cornea. Unlike the Goldmann tonometer, it does not require the use of anesthetic drops.

2. Non-Contact Tonometry (Air-Puff Tonometry)

Non-contact tonometry (NCT) is an alternative to applanation tonometry that uses a device, such as the air puff tonometer, to measure IOP. This method is non-invasive and does not require anesthetic drops, making it a popular choice in optometric practice. However, NCT is less accurate than applanation tonometry and may be affected by corneal thickness. Reichert 7 and Frey TN-100 are automated non-contact tonometers that can be easily operated by optometrists, nurses, and ophthalmic technicians.

Advanced tools such as the Frey TNP-200 and the Reichert ORA G7 have revolutionized the way clinicians diagnose and manage glaucoma by providing additional information beyond traditional tonometry methods.

The Frey TNP-200 combines non-contact tonometry with a pachymeter to measure corneal thickness, which can affect the accuracy of IOP measurements. This device provides corrected IOP readings that are more accurate, even in patients with abnormal corneal thickness and curvature, thanks to its built-in advanced algorithm that compensates for corneal properties.

The Reichert ORA G7 measures corneal hysteresis, which is an important biomechanical property that can affect the accuracy of IOP measurements and is a risk factor for the development and progression of glaucoma. This device uses a rapid air pulse to measure corneal hysteresis, providing clinicians with a corneal-compensated IOP reading that is more accurate and reliable than traditional tonometry methods.

3. Rebound Tonometry

Rebound tonometry uses a device, such as the Suoer Sw-500, to measure IOP by bouncing a small probe off the cornea and measuring the rebound velocity. This method is non-invasive and easy to use, making it suitable for various clinical settings. Rebound tonometry is also non-invasive and does not require the use of topical anesthetics.

In conclusion, while the Goldmann tonometer remains the gold standard for IOP measurement, non-contact tonometry and rebound tonometry are popular choices in optometric practice due to their ease of use. Advanced tools such as the Frey TNP-200 and the Reichert ORA G7 provide additional information beyond traditional tonometry methods, improving the accuracy and reliability of IOP measurements in patients with glaucoma.