What is the name of the device used to check eye pressure?

Devices for Measuring Eye Pressure (Tonometers)

The primary device used to check eye pressure is the Goldmann applanation tonometer (GAT), which is considered the gold standard for measuring intraocular pressure (IOP). 1

Types of Tonometers

Contact Tonometers

1. Goldmann Applanation Tonometer (GAT)

   • Mounted to a slit lamp
   • Requires topical anesthesia
   • Measures IOP by flattening a small area of the central cornea
   • Considered the gold standard for IOP measurement
   • Identifies the "just-touching" inside edges of semicircular mires viewed through the prism tip

2. Dynamic Contour Tonometer (Pascal technique)

   • Uses a piezoresistive sensor embedded in the tonometer tip
   • Samples IOP 100 times per second
   • Concave tip shape minimizes influence of corneal properties
   • Requires topical anesthesia
   • Mounted to the slit lamp
   • Calculates IOP independent of corneal properties

3. Rebound Tonometer (iCare)

   • Uses an induction coil to magnetize a small plastic-tipped metal probe
   • Rapidly fires probe against cornea (0.25 m/sec)
   • Analyzes deceleration rate and contact time
   • Does not require topical anesthesia
   • Requires six measurements for accuracy

4. Mackay-Marg Tonometer

   • Handheld, battery-powered device
   • Combines applanation and indentation mechanisms
   • Has a small applanating plunger
   • Requires topical anesthesia
   • Multiple readings are averaged

Non-Contact Tonometers

1. Air-Puff Tonometer (Non-Contact Tonometer)

   • Uses a collimated air pulse to deform the cornea
   • Does not require topical anesthesia
   • Commonly used for screening purposes
   • Tends to measure IOP higher than GAT by 2-6 mmHg 2, 3

2. Ocular Response Analyzer

   • Uses bidirectional applanation process with air pulse
   • Measures biomechanical properties of cornea (hysteresis)
   • Calculates "corneal-compensated" and GAT-equivalent IOP
   • Does not require topical anesthesia
   • Also measures ocular pulse amplitude

Clinical Considerations

Accuracy and Reliability

• GAT remains the most reliable method for measuring IOP 2
• Non-contact tonometers typically measure IOP higher than GAT, especially at higher pressure readings 2, 4
• Central corneal thickness (CCT) affects all tonometry readings, with non-contact tonometry being most affected 4, 3

Special Circumstances

• In diseased or post-surgical corneas, GAT may be very inaccurate due to:
  • Alterations in corneal thickness
  • Changes in hydration state
  • Corneal curvature/astigmatism
  • Irregular corneal epithelial surface
  • Corneal stromal scarring 1

Clinical Practice

• For routine screening, non-contact tonometers are suitable 4
• For accurate diagnosis and management of glaucoma, GAT is preferred 2, 3
• For patients with corneal abnormalities, alternative techniques should be used 1
• Consistency in using the same device for follow-up measurements is important for detecting meaningful IOP changes 1

Common Pitfalls

• Relying solely on non-contact tonometry for definitive diagnosis can lead to unnecessary referrals, particularly in patients with thicker corneas 3
• Not accounting for the effect of central corneal thickness on IOP measurements
• Using different tonometers for follow-up measurements, making trend analysis difficult
• Not recognizing the limitations of GAT in diseased corneas

When selecting a tonometer for clinical use, consider the specific patient population, the need for accuracy versus convenience, and the presence of any corneal abnormalities that might affect measurements.