Free CPO Tonometry Principles and Procedures Questions and Answers

Question 1

What is considered the 'gold standard' for measuring intraocular pressure (IOP)?

Accepted Answer

Goldmann applanation tonometry (GAT)

Answer

Goldmann applanation tonometry (GAT) is widely regarded as the most accurate and reliable method for measuring IOP. It serves as the benchmark against which other tonometers are compared. The procedure involves using a special prism at the slit lamp to flatten a small area of the cornea.

Question 2

The Goldmann tonometer measures IOP based on the Imbert-Fick principle, which relates pressure to the ______ required to flatten a specific area of a sphere.

Accepted Answer

Force

Answer

The Imbert-Fick law states that for an ideal, dry, thin-walled sphere, the pressure inside is equal to the force applied to flatten its surface divided by the area of flattening. The Goldmann tonometer is designed to apply this principle to the cornea by measuring the force needed to flatten a 3.06mm diameter area.

Question 3

Which of the following factors can cause a falsely LOW IOP reading with Goldmann tonometry?

Accepted Answer

A thin central cornea

Answer

Corneal thickness affects the accuracy of GAT. A cornea that is thinner than average provides less resistance to flattening, resulting in an artificially low IOP reading. Conversely, a thick cornea can lead to a falsely high reading.

Question 4

When taking a measurement with a Goldmann tonometer, the correct endpoint is reached when the inner edges of the two fluorescent semi-circles (mires) are:

Accepted Answer

Just touching

Answer

The operator adjusts the force dial until the inner margins of the green semi-circles, viewed through the prism, are just touching. If they overlap, the pressure reading will be too high; if they are separated, the reading will be too low. This alignment indicates the correct area of the cornea has been flattened.

Question 5

How does a non-contact tonometer (NCT), or 'air-puff' tonometer, measure intraocular pressure?

Accepted Answer

By measuring the corneal response to a puff of air

Answer

The NCT emits a controlled puff of air towards the cornea. An optical sensor measures the time it takes for the air to flatten a small, specific area of the corneal surface; a higher pressure inside the eye requires a stronger puff (or shorter time at a set force) to achieve flattening.

(CPO) Certified Paraoptometric Practice Test

(CPO) Certified Paraoptometric Practice Test

Free CPO Tonometry Principles and Procedures Questions and Answers