Illustration of an eye exam with a tonometer, showing potential for misalignment.

Eye Pressure Checks: Are You Getting the Right Angle?

Theo Raines in Health & Wellness August 2025 • 4 min read.

"Exploring how slight misalignments during rebound tonometry can affect your intraocular pressure readings and what it means for your eye health."

Intraocular pressure (IOP) measurement is a critical part of routine eye exams, especially for those at risk of glaucoma or other eye conditions. One of the tools used to measure IOP is the rebound tonometer, known for being quick and relatively comfortable. Unlike the traditional Goldmann applanation tonometer (GAT), rebound tonometers don't require numbing eye drops, making them a popular choice for both practitioners and patients.

However, the accuracy of any measurement tool can be affected by how it's used. This article delves into a study investigating how small misalignments during rebound tonometry can influence the readings. The goal is to help you, the patient, better understand the factors that contribute to accurate IOP measurements and what questions to ask during your eye exam.

The study we're discussing focused on the iCare TA0li rebound tonometer and examined how lateral and angular deviations of the probe affected IOP readings. By understanding these potential sources of error, we can all work together—patients and eye care professionals—to ensure the most accurate assessment of your eye health.

Decoding the Study: Misalignment and Your IOP

Illustration of an eye exam with a tonometer, showing potential for misalignment.

Researchers at Aston University used a precise alignment rig to measure IOP in healthy volunteers. They compared IOP readings taken with the iCare tonometer at the central corneal apex (the ideal location) to readings taken with slight misalignments—both laterally (2mm nasally and temporally) and angularly (5° and 10° nasally and temporally). Goldmann applanation tonometry (GAT), the clinical gold standard, was also used as a benchmark.

Here's what the study revealed:

iCare Overestimation: The iCare tonometer tended to read higher than the GAT, confirming previous findings.
Lateral Shifts: Small lateral misalignments (2mm) didn't significantly alter IOP readings.
Angular Deviations: Only a 10° nasal deviation of the probe resulted in a statistically significant (but clinically small) underestimation of IOP.

These findings suggest that the iCare rebound tonometer is fairly robust when it comes to minor misalignments in healthy eyes. However, it's crucial to remember that this study was conducted on healthy subjects. The impact of misalignment might be more pronounced in individuals with corneal irregularities or other eye conditions.

What This Means for Your Eye Health

While the study indicates that minor misalignments during rebound tonometry may not significantly impact IOP readings in healthy eyes, it's always best to ensure the measurement is taken as accurately as possible. This is particularly important if you have risk factors for glaucoma or other eye conditions.

Here are some points to consider:

Ask your eye care provider about their technique for IOP measurement and what steps they take to ensure accuracy. If you have any concerns about the readings or the testing process, don't hesitate to voice them. Remember, you are a partner in your eye health.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1155/2013/791084, Alternate LINK

Title: Does Rebound Tonometry Probe Misalignment Modify Intraocular Pressure Measurements In Human Eyes?

Subject: Ophthalmology

Journal: Journal of Ophthalmology

Publisher: Hindawi Limited

Authors: Ian G. Beasley, Deborah S. Laughton, Benjamin J. Coldrick, Thomas E. Drew, Marium Sallah, Leon N. Davies

Published: 2013-01-01

Everything You Need To Know

What is Intraocular Pressure (IOP) and why is it important?

Intraocular pressure (IOP) is a measurement of the fluid pressure inside your eye. This pressure is crucial to maintain the shape and function of the eye. High IOP can be a sign of glaucoma, a condition that can damage the optic nerve and lead to vision loss. Regular eye exams, including IOP checks, are essential for monitoring eye health, especially for those at risk of glaucoma.

What is rebound tonometry?

Rebound tonometry is a method used to measure Intraocular Pressure (IOP). It involves using a device, such as the iCare tonometer, that gently touches the eye to assess the pressure. Unlike the Goldmann applanation tonometer (GAT), rebound tonometry doesn't require numbing eye drops, making it more convenient for patients. It's considered a quick and comfortable way to measure IOP during eye exams.

What is the iCare tonometer?

The iCare tonometer is a specific type of rebound tonometer. The study used the iCare TA0li model to examine how accurate IOP readings were with different misalignments. The results of the study can be helpful for understanding how the iCare tonometer works, and the limitations of the device. This helps patients and eye care professionals to understand the importance of accurate measurements.

What does misalignment mean in the context of rebound tonometry, and why is it important?

Misalignment in rebound tonometry refers to the probe of the tonometer not being perfectly aligned with the center of the cornea. The study looked at how lateral (side-to-side) and angular (angle) misalignments affected IOP readings. The researchers discovered that small lateral misalignments didn't significantly change the readings. However, angular deviations, particularly a 10° nasal deviation, resulted in a noticeable underestimation of IOP. This is important because it can impact the accuracy of IOP measurement and affect the diagnosis and management of eye conditions.

What is Goldmann applanation tonometry (GAT), and how is it used in eye exams?

Goldmann applanation tonometry (GAT) is the clinical 'gold standard' for measuring Intraocular Pressure (IOP). It's used as a benchmark to compare the accuracy of other methods, like rebound tonometry. The study used GAT to compare its findings with the iCare tonometer. The GAT method is known for accuracy but requires numbing eye drops and can be slightly less comfortable. The study found the iCare tonometer, while generally accurate, tended to read higher than GAT.