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David B. Usher, Marc D. Friedman, Radha Pertaub, David Muller; Interferometric System for Topographic and Biomechanical Study of the Cornea. Invest. Ophthalmol. Vis. Sci. 2012;53(14):136.
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To evaluate the use of a dynamic interferometric device for analyzing temporal corneal topographic changes under varying intraocular pressures (IOP) and corneal tear film dynamics.
A proprietary dynamic interferometer was used to acquire sequences of interferograms from porcine eyes in vitro and with a single human subject in vivo. The interferometer was suspended vertically on a rail with mounted optics used to create a converging cone of light corresponding to a 12 mm radius of curvature for the porcine eyes and 7.5 mm for the human eye. A reference waveform was created using a suitable plane convex optic in each case. Illumination was supplied by a 633 nm HeNe laser (~0.5mW output). A micrometer stage was used to align the porcine eye with the laser. Eye drops were applied prior to each measurement. Camera exposures ranging from 66 to 330 µs were used to record sequences of interferograms as the IOP was varied using a saline column. In the case of the human eye the variation in IOP was provided by the naturally occurring cardiac cycle. Sequences of interferograms were also recorded during the application of various types of OTC eye drops.
The interferometer recorded sequences of interferograms. Displacements of the corneal surface were measured dynamically with increasing IOP. Increases in IOP of approximately 5 mmHg produced corneal surface displacements ranging from 2.4 to 5.4 µm in the porcine eyes. In the case of the human eye, a pulsation of the corneal surface of a period equal to the cardiac cycle was observed. Tear film breakup was clearly observable in real time across the porcine eyes and the dynamics of the flow of the different types of OTC eye drops was measurable.
The rapid exposure times and high acquisition rates of the interferometer makes it well suited to dynamic corneal topography and tear film dynamics. This study demonstrated that this interferometric device may also be used to dynamically measure biomechanical properties of corneas in vivo by correlating ocular pulse IOP amplitudes with corneal displacements. Further customization of this method for corneal applications is ongoing.
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