science

Imbert-Fick law

Imbert-Fick law is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Imbert-Fick law rather than just read about it. In short: Armand Imbert (1850–1922) and Adolf Fick (1829–1901) both demonstrated, independently of each other, that in ocular tonometry the tension of the wall can be neutralized when the application of the tonometer produces a flat surface instead of a convex one, and the reading of the tonometer (P) then equals (T) the IOP," whence all forces cancel each other. History This principle was used by Hans Goldmann (1899–1991) wh…

Key takeaways

Imbert-Fick law belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Imbert-Fick law to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Imbert-Fick law from memory before moving on to harder problems.

Reference excerpt

Armand Imbert (1850–1922) and Adolf Fick (1829–1901) both demonstrated, independently of each other, that in ocular tonometry the tension of the wall can be neutralized when the application of the tonometer produces a flat surface instead of a convex one, and the reading of the tonometer (P) then equals (T) the IOP," whence all forces cancel each other.

History This principle was used by Hans Goldmann (1899–1991) who referred to it as the Imbert-Fick "law", thus giving his newly marketed tonometer (with the help of the Haag-Streit Company) a quasi-scientific basis; it is mentioned in the ophthalmic and optometric literature, but not in any books of physics. According to Goldmann, "The law states that the pressure in a sphere filled with liquid and surrounded by an infinitely thin membrane is measured by the counterpressure which just flattens the membrane." "The law presupposes that the membrane is without thickness and without rigidity...practically without any extensibility." A sphere formed from an inelastic membrane and filled with incompressible liquid cannot be indented or applanated even when the pressure inside is zero, because a sphere contains the maximum volume with the minimum surface area. Any deformation necessarily increases surface area, which is impossible if the membrane is inelastic. The physical basis of tonometry is Newton's third law of motion: "If you press an eyeball with an object, the object is also pressed by the eyeball." The law is this:

Intraocular pressure = Contact force/Area of contact The law assumes that the cornea is infinitely thin, perfectly elastic, and perfectly flexible. None of these assumptions are accurate. The cornea is a membrane that has thickness and offers resistance when pressed. Therefore, in Goldmann tonometry, readings are normally taken when an area of 3.06mm diameter has been flattened. At this point the opposing forces of corneal rigidity and the tear film are roughly approximate in a normal cornea and cancel each other out allowing the pressure in the eye to be inferred from the force applied.

Worked examples

Example 1 — a first encounter with Imbert-Fick law

Start with the simplest possible case. Write down what Imbert-Fick law claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Imbert-Fick law before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Imbert-Fick law ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Imbert-Fick law

In research: Imbert-Fick law appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Imbert-Fick law in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Imbert-Fick law is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ophthalmology, Pressure, so understanding it makes those chapters shorter.
In everyday life: Look for Imbert-Fick law outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Imbert-Fick law in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Imbert-Fick law means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Imbert-Fick law out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Imbert-Fick law in simple terms?

Why does Imbert-Fick law matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Imbert-Fick law?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Imbert-Fick law.