Tonometer, Applanation Tonometer

A tonometer is a medical instrument, Ophthalmic equipment used to measure the intraocular pressure (IOP) in the eye, which helps diagnose and monitor conditions such as glaucoma. 

The tonometer on a slit lamp is used to measure the intraocular pressure (IOP) of the eye. There are a few different types of tonometers, but one common method used on slit lamps is called an applanation tonometer.

An applanation tonometer measures IOP by gently flattening a small area of the cornea. This is done by applying a slight force to the surface of the eye. The tonometer has a small probe with a flat surface that is brought into contact with the cornea. Some tonometers use a small amount of anesthetic eye drops to numb the eye before the measurement is taken.

The tonometer probe is attached to a pressure sensor which measures the force needed to flatten the cornea. This force is then converted into a pressure measurement, providing an estimate of the IOP. The results are typically displayed on a scale or digitally on the slit lamp's interface.

There are a few different types of tonometer

1. Applanation Tonometers: These tonometers, as mentioned earlier, flatten a small area of the cornea by applying a gentle force. They measure the resistance of the cornea to obtain the IOP reading.

2. Non-Contact (Air Puff) Tonometers: This type of tonometer does not require direct contact with the cornea. Instead, it uses a puff of air to measure the IOP. The tonometer calculates IOP based on the changes in the cornea caused by the air pulse.

3. Rebound Tonometers: These tonometers use a small probe that is gently applied to the cornea. The probe measures the rebound speed of a tiny metallic tip after it touches the cornea. The IOP is estimated based on this rebound speed.

4. Goldman Applanation Tonometers: These tonometers have a prism that is gently applied to the cornea after the surface has been numbed with eye drops. The tonometer then measures the amount of force required to flatten the cornea.

Frequently Asked Questions

Q: What is the purpose of a tonometer?

A: A tonometer is used to measure the intraocular pressure to check for abnormalities that might indicate conditions like glaucoma.

Q: How does a tonometer work?

A: There are several types of tonometers, but the most common one is the applanation tonometer. It measures IOP by gently flattening a small area on the cornea and measuring the force required to do so.

Q: Is tonometry a painful procedure?

A: No, tonometry is generally painless. Some patients may experience mild discomfort or have a reflex urge to blink during the procedure.

Q: Can I measure intraocular pressure at home using a tonometer?

A: There are portable tonometers available for home use, but it's always best to consult with an eye care professional for accurate readings and proper guidance on its usage.

Q: Are there any risks or side effects associated with tonometry?

A: The risks associated with tonometry are minimal. In rare cases, the procedure can cause temporary blurred vision, corneal abrasions, or eye infections, but these complications are extremely uncommon.

Q: How often should I have my intraocular pressure checked?

A: The frequency of tonometry measurements depends on various factors, including your age, family history, and overall eye health. Your eye doctor can recommend the appropriate interval for you, but generally, it is recommended to have IOP checked at least once every one to two years.