Applanation Tonometry Explained | Imbert-Fick Principle | Optometry MCQ Series

Applanation Tonometry Explained | Imbert-Fick Principle | Optometry MCQ Series

Question: Applanation tonometry is based on:

A. Imbert-Fick principle

B. Goldman's equation

C. Perkins principle

D. Principle of indentation

Correct Answer:

A. Imbert-Fick principle

Explanation:

Applanation tonometry is a method used to measure intraocular pressure (IOP) — the pressure inside the eye. The most common type of applanation tonometer is the Goldmann Applanation Tonometer.

What is the Imbert-Fick Principle?

The Imbert-Fick principle states that:

> The pressure inside a sphere is equal to the force required to flatten its surface divided by the area of flattening.

Formula:

P = F / A

Where:

P = intraocular pressure

F = force applied to flatten the cornea

A = area of the cornea flattened

This principle assumes the sphere is:

• Perfectly spherical

• Dry

• Thin-walled

• Infinitely flexible

Of course, the human eye doesn’t meet all these conditions exactly, but the Goldmann tonometer was designed to minimize the impact of these limitations.

What about the other options?

B. Goldmann's equation: While Goldmann devised the tonometer, the device is based on the Imbert-Fick principle, not a separate equation.

C. Perkins principle: Perkins tonometer is a portable version of the Goldmann tonometer; it also works on the Imbert-Fick principle.

D. Principle of indentation: This applies to Schiotz tonometry, not applanation tonometry.

We explain how applanation tonometry—especially Goldmann applanation tonometry—works by applying the Imbert-Fick law, which relates the pressure inside a sphere to the force required to flatten its surface.

Perfect for students and professionals in optometry, ophthalmology, and eye care, this video boosts your understanding of IOP testing, glaucoma screening, and clinical procedures.

Keywords:

applanation tonometry, Imbert-Fick law, intraocular pressure, Goldmann tonometer, eye pressure test, optometry mcq, glaucoma diagnosis, IOP measurement, tonometry basics

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