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K. Terai, J. Yamada, S. Kinoshita; Development of a New Method for the Measurement of Corneal Rigidity. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3532.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a new method for the measurement of corneal rigidity and to determine its usefulness for clinical applications.
A new tip was developed for the applanation part of a Goldman applanation tonometer that can be projected hemisperically (projection tip) to obtain intraocular pressure (IOP) values. IOP values obtained by use of this projection tip were then compared with IOP values obtained by use of the normal tip. To test the projection tip, artificial eyes were developed to be bonded with artificial corneas constructed of silicone of various rigidities, and then connected to a water bottle. After positioning the water bottle at various heights in relation to the artificial eyes, IOP measurements were first obtained by use the normal tip, followed by measurements obtained by use of the projection tip. Next, the IOP of 44 human normal eyes and 24 human keratoconus eyes were similarly measured, and the corneal thickness of those eyes was then measured by use of a corneal ultrasonic pachymeter.
Measurement of the artificial corneas made of silicone confirmed that the measured IOP values were influenced by the height of the bottle and the corneal rigidity, and that the IOP values obtained by measurement with the normal tip were not similar to those obtained by measurement with the projection tip. In the human normal eyes, the differences between the IOP values obtained by measurement using the projection tip and those obtained by measurement using the normal tip were well-correlated with the corneal thickness values obtained by measurement with the pachymeter. A calculation made by using the values measured by projection tip, the values measured by normal tip, and the corneal thickness values based on these data showed that early-phase keratoconus corneas with a thickness of 500µm or more were easily distinguishable from normal corneas.
The results of this study showed that it was possible to measure corneal rigidity by use of this newly developed method. In addition, we feel that it is less expensive and easier to use this new method than the methods that are currently in existence. Although ophthalmologists currently use the analysis of the shape of the cornea mainly as a tool for the diagnosis of keratoconus, this new method can be used to detect potential keratoconus prior to corneal transformation. Therefore, this method may be useful for inspecting the cornea prior to refractive surgery.
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