Measuring Eye Pressure

There are many methods your eye doctor may use to monitor and check your eye pressure.  Eye pressure is a huge risk factor for causing glaucoma - the second leading cause of blindness in the world.

We are observing national Glaucoma Awareness Month.  The World Health Organization has designated each January to annually increase awareness of glaucoma.  Glaucoma can affect anyone. By increasing your knowledge of glaucoma, we hope your sight, or that of someone you know, may be saved by the early diagnosis and treatment of glaucoma.

Eye Pressure

There are many types of glaucoma.  Glaucoma causes damage to the optic nerve.  While the exact mechanism of this occurs is not precisely known, high eye pressure is a large risk factor developing glaucoma.

During most eye exams, your eye pressure is usually recorded for screening purposes.  Higher than normal eye pressure may indicate glaucoma.

The process of measuring your eye pressure is called tonometry.  There are several common tonometers your doctor may choose to measure eye pressure:

1. Air Puff Tonometry (AP)
2. Hand held Tono-Pen
3. Goldmann Applanation (GA)

Air Puff Tonometer

This is a non-contact method of measuring IOP (intraocular pressure) and is a great screening tool.  The air puff allows the tonometer (machine) to measure the corneal resistance to the stream of air.

Advantages of the AP (air puff tonometer) are that it does not touch the eye, is quick and can serve as a great screening tool.

Disadvantage of the AP is that it generally overestimates the eye pressure, giving falsely high IOP.  (This is not necessarily a bad attribute).

Tono-Pen

This is a hand held device used to quickly measure the eye pressure.  

A numbing drop is placed on the eye and the tip of the Tono-Pen gently touches the eye.  It is painless and avoids the difficulty of fitting the patient into the slit lamp.

Advantages of the Tono-Pen are the ease of use (learning curve of examiner/technician is very low) and speed.

Cons:  Tono-Pens are expensive and require replacement of tip covers for each measurement.  Moreover, the Tono-Pen may have accuracy issues at the extremes of pressure measurement.  .Overall, it is commonly used due to it’s ease of use and comparable accuracy to the Goldmann Applanation Tonometer (GAT).

Goldmann Applanation Tonometry (GAT)

This is the gold standard.  

A drop of yellow/orange/green fluorescein dye mixed with anesthetic is placed on the eye.  A conical piece of plastic is gently (and painlessly) placed on the eye. A blue light measures the endpoint when exact IOP has been measured.

Advantages:  Gold standard for measuring IOP.

Disadvantages:  Difficult to learn and requires experience.  Cross-contamination is possible.

Eye pressure is the largest risk factor to developing glaucoma.  Depending upon the situation, varying techniques and tools have been developed to quickly and accurately assess a patient’s IOP looking to determine those at risk.