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I. Pallikaris, H.S. Ginis, D. De Brouwere, M.K. Tsilimbaris; A Novel Instrument for the Non–Invasive Measurement of Intraocular Pressure and Ocular Rigidity . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2268.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a minimally invasive device capable of measuring intraocular pressure (IOP) and ocular rigidity. Moreover, to perform pilot measurements and compare this device in terms of IOP measurement with Goldman Applanation Tonometry (GAT).
The device consists of a glass lens that is used to contact and deform the corneal surface. A wide infrared beam is propagated through the lens and cornea. Partial index matching at the area of contact modulates the back reflected intensity of the beam according to the diameter of the applanated corneal zone. This optical sensor is mounted on a load cell that measures the force required to achieve the above–mentioned deformation. Signals both from the opto–electronic sensor and the force sensor are pre–amplified and captured by means of an analog to digital converter PC card for post processing. For any given area of contact the displaced volume can be calculated. The rigidity of the eye is calculated as the slope of the IOP vs displaced volume curve.
Pressure calibration: The device was calibrated by taking measurements on enucleated rabbit eyes mounted on a purposely constructed base. Rabbit eyes IOP was adjusted and maintained constant during the measurements by means of a saline column connected to the anterior chamber through a 22–gauge catheter inserted at the limbus. The pressure was verified by means of a pressure transducer. Comparative measurements: Ten eyes of ten subjects were enrolled in the initial evaluation of the instrument in comparison to GAT.
In the measured eyes average IOP using the Goldman applanation tonometer was 10.6 mmHg (Range 9 to 12 SD=0.96). The average IOP as estimated by the device was 9.99 mmHg (Range 7.3 to 13, SD=2.18). This difference was not statistically significant. The average rigidity estimated by means of the device was 0.26 mmHg/microliter (Range 0.13 to 0.48 SD=0.11).
The device can measure intraocular pressure. The variability of the measurements is higher than that of Goldman Applanation Tonometry. The calculated values of ocular rigidity are comparable to values reported in the literature.
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