What is a Tonometer?

By Alex | September 16, 2025

At Insight Eye Equipment, we support clinics with refurbished tonometers and practical guidance. This page explains what a tonometer is, why intraocular pressure (IOP) matters in clinical decision-making, and how different measurement methods fit into your workflow.

Quick Answer: Understanding the Tonometer

Intraocular pressure (IOP) refers to the fluid pressure inside the eye, a key factor in maintaining optic nerve health. A tonometer measures this pressure in millimeters of mercury (mmHg), providing clinicians with an important parameter for assessing glaucoma risk and guiding treatment decisions.

Types of Tonometers

Tonometers are essential diagnostic tools used to measure intraocular pressure (IOP), a key factor in the detection and management of glaucoma. Several types are available, each suited to different clinical environments:

  • Applanation Tonometers – Considered the standard in many practices, these devices flatten a small area of the cornea to calculate IOP with high accuracy.
  • Non-Contact (Air-Puff) Tonometers – Use a gentle puff of air to measure corneal response without direct contact, offering speed and comfort for routine screening.
  • Rebound Tonometers – Portable units that measure IOP using a small probe, useful in pediatrics or settings where traditional contact methods are difficult.
  • Transpalpebral Tonometers – Measure IOP through the eyelid or sclera, offering an option when corneal contact is not possible.

Types of Tonometers We Offer

At Insight Eye Equipment, we focus on refurbished tonometers that combine accuracy, efficiency, and patient comfort. Our current selection includes:

  • AccuPen Handheld Applanation Tonometer – Portable applanation device featuring Gravity Offset Technology and micro strain-gauge technology with proprietary algorithms for reproducible IOP readings.
  • Keeler Pulsair IntelliPuff NCT – Handheld, non-contact system using IntelliPuff® electronic + optical technology to deliver fast, comfortable IOP measurements.

How Tonometers Work

Functionally, tonometers assess corneal response to force or displacement (applanation, rebound, non-contact). Indentation instruments are less common in modern clinics, and contact-lens–based sensors are emerging options for diurnal IOP profiling.

When & Why It’s Used

We rely on tonometry in several scenarios:

  • Routine glaucoma assessment in patients with risk factors (e.g., family history, diabetes, steroid use), per clinical judgment.
  • Diagnosing and monitoring ocular hypertension and assessing treatment effectiveness in glaucoma patients.
  • Evaluating eye injuries or inflammation that may affect intraocular pressure.

Preparing & What to Expect

Before your tonometry appointment, here’s how to prepare and what you’ll experience:

  • Preparation
    • Remove contact lenses and heavy eye makeup.
    • No fasting or medication adjustments needed.
  • During the test
    • You’ll sit at a slit lamp or stand at the non-contact device.
    • For applanation, we apply numbing drops and a tiny amount of fluorescein dye.
    • Applanation or rebound devices briefly contact the cornea; non-contact systems use an air pulse and do not touch the cornea.
  • After the test
    • Anesthetic wears off in minutes; you may feel brief watering or mild irritation.
    • We’ll review your IOP result with you right away.
    • Interpreting Results & Risks

Your ophthalmologist look at what your IOP readings mean and potential risks:

  • Normal Range
    • Typical IOP range is about 10–21 mmHg, but optic nerve health depends on multiple factors; some patients have glaucoma with IOP in this range (normal-tension glaucoma)
  • High IOP
    • Elevated IOP (often >21 mmHg) increases glaucoma risk and warrants comprehensive evaluation (e.g., optic nerve assessment, visual fields, OCT). Goldmann applanation remains the reference standard for IOP measurement, but diagnosis is not based on IOP alone.
  • Low IOP
    • ~6–6.5 mmHg or less is often used as a statistical threshold for hypotony. Clinical concern depends on symptoms/signs (e.g., maculopathy, corneal edema). Prompt evaluation is warranted.
  • Risks & Accuracy Factors
    • Transient redness or irritation can occur; rare corneal abrasion is possible with contact methods. Measurements can be influenced by corneal thickness (CCT), astigmatism, scarring, or prior corneal surgery; technique and calibration are important.

Final Thoughts on Tonometers

Regular IOP measurement is central to glaucoma care and overall ocular health. At Insight Eye Equipment, we provide refurbished applanation and non-contact tonometers, fully recalibrated, warrantied, and supported with white-glove delivery, to help your team capture accurate readings and streamline workflow.

Posted in knowledge center