Ultrasound signal processing for characterization and enhanced biometry of the cornea

Purpose: The cornea acts as the window of the eye's optical system, and its chief refractive component. The lack of intervening tissues makes the cornea accessible to very high frequency ultrasonic study. In this report, we detail use of radiofrequency (RF) signal processing methods to characterize corneal pathology and to enhance biometric precision. Methods: Using a 50 MHz PVDF transducer, we scanned the cornea using an arc motion so as to maintain normality and consistent range. RF data were acquired at a sample rate of 500 MHz. Deconvolution against a glass-plate echo allowed biometric enhancement (by effectively broadening the bandwidth) and measurement of tissue backscatter spectra. Results: Calibrated spectrum analysis was used to quantitatively measure backscatter in corneal scars and other pathologies. Signal processing allowed us to attain reproducibility for repeated measurements of the corneal epithelium (approximately 50 microns thick) to 1 micron. By combining measurements from a series of planes, maps of the thickness of the individual layers comprising the cornea were produced. Conclusion: The layers of the cornea have different optical refractive indices, and thus their thicknesses directly affect visual acuity. The scattering of light by a corneal scar is caused by inhomogeneities or irregularities that may result in acoustic backscatter as well. The ability of ultrasound to quantify backscatter and corneal layer thickness provides a new avenue for diagnosis of corneal disease and refractive abnormalities.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.