Imbert-Fick law: Difference between revisions
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The '''Imbert-Fick "law"''' was invented by Hans Goldmann (1899–1991) to give his newly marketed [[tonometer]] (with the help of the Haag-Streit Company) a quasi scientific basis; it is mentioned in the [[Ophthalmology|ophthalmic]] and [[Optometry|optometric]] literature, but not in any books of [[physics]]. According to Goldmann <ref>Goldmann H. Applanation Tonometry. Transactions Second Glaucoma Conference. New York, Josiah Macy, Jr Foundation. 1957.</ref> "The law states that the pressure in a sphere filled with liquid and surrounded by an infinitely thin [[Biological membrane|membrane]] is measured by the counterpressure which just flattens the membrane." "The law presupposes that the membrane |
The '''Imbert-Fick "law"''' was invented by Hans Goldmann (1899–1991) to give his newly marketed [[tonometer]] (with the help of the Haag-Streit Company) a quasi scientific basis; it is mentioned in the [[Ophthalmology|ophthalmic]] and [[Optometry|optometric]] literature, but not in any books of [[physics]]. According to Goldmann <ref>Goldmann H. Applanation Tonometry. Transactions Second Glaucoma Conference. New York, Josiah Macy, Jr Foundation. 1957.</ref> "The law states that the pressure in a sphere filled with liquid and surrounded by an infinitely thin [[Biological membrane|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." |
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The problem is that a [[sphere]] formed by such a membrane and filled with [[incompressible]] liquid (water) cannot be indented or applanated even when the pressure inside in zero, because a sphere contains the maximum volume with the minimum surface area. <ref>Koster W. Beitraege zur Tonometrie und Mnometrie des Auges. Graefe's Arch.Ophthalmol. 1895; 41: 113-158.</ref><ref> Markiewitz HH. The so-called Imbert-Fick Law. AMA Arch.Ophthalmol. 1960; 64: 189/159.</ref>. Any [[deformation]] necessarily increases [[surface area]], which is impossible if the membrane is inelastic, such as [[aluminum foil]]. |
The problem is that a [[sphere]] formed by such a membrane and filled with [[incompressible]] liquid (water) cannot be indented or applanated even when the pressure inside in zero, because a sphere contains the maximum volume with the minimum surface area. <ref>Koster W. Beitraege zur Tonometrie und Mnometrie des Auges. Graefe's Arch.Ophthalmol. 1895; 41: 113-158.</ref><ref> Markiewitz HH. The so-called Imbert-Fick Law. AMA Arch.Ophthalmol. 1960; 64: 189/159.</ref>. Any [[deformation]] necessarily increases [[surface area]], which is impossible if the membrane is inelastic, such as [[aluminum foil]]. |
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Revision as of 13:43, 5 October 2010
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The Imbert-Fick "law" was invented by Hans Goldmann (1899–1991) to give 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 [1] "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."
The problem is that a sphere formed by such a membrane and filled with incompressible liquid (water) cannot be indented or applanated even when the pressure inside in zero, because a sphere contains the maximum volume with the minimum surface area. [2][3]. Any deformation necessarily increases surface area, which is impossible if the membrane is inelastic, such as aluminum foil.
The actual physical basis of tonometry if Newton's third law of motion: "If you press a stone [eyeball] with your finger, the finger is also pressed by the stone [eyeball}."
The law is this: Intraoccular Pressure = Contact Force / Area of contact
The law assumes that the cornea is infinitely thin, perfectly elastic, and perfectly flexible. [4] None of these assumptions are true. The cornea is a membrane that has thickness and offers resistance when pressed. [5]
Notes
- ^ Goldmann H. Applanation Tonometry. Transactions Second Glaucoma Conference. New York, Josiah Macy, Jr Foundation. 1957.
- ^ Koster W. Beitraege zur Tonometrie und Mnometrie des Auges. Graefe's Arch.Ophthalmol. 1895; 41: 113-158.
- ^ Markiewitz HH. The so-called Imbert-Fick Law. AMA Arch.Ophthalmol. 1960; 64: 189/159.
- ^ Whitacre, MM, Stein, R. (1993) Sources of error with use of Goldmann-type tonometers Surv Ophthalmol 38,1-30
- ^ Anders Eklund, Per Hallberg, Christina Lindén, and Olof A. Lindahl. (2003) An Applanation Resonator Sensor for Measuring Intraocular Pressure Using Combined Continuous Force and Area Measurement