Optical coherence tomography (OCT) is an emerging imaging modality. It provides in vivo cross-sectional images with micron level resolution. OCT is attractive for imaging the anterior eye segment because of its characteristics on high resolution, non-contact, and easy anatomical interpretation. The fast data acquisition rate (>2000 axial scans per second) of current anterior segment OCT systems allows the measurement of corneal dimensions without significant motion error. It also generates huge amount of data. Manual anatomic reconstruction and measurement are time consuming and operator-dependent. Automated image processing and analysis techniques can overcome these limitations and make routine clinical use of OCT possible.
A “dewarping” method was developed to remove the distortion due to refraction and transition of the group index at the interfaces. Image averaging and smooth filtering techniques were used to suppress the speckle noise. Image segmentation algorithms were developed to automatically detect the anterior and posterior corneal boundaries and the LASIK flap interface. The boundaries detected by the computer algorithm were compared with manual segmentation results to evaluate the performance of the algorithm.
Three clinical studies had been conducted to investigate the anterior segment OCT applications in corneal thickness mapping, keratoconus screening, and LASIK thickness measurements.
The results showed that: 1. The anterior segment OCT could accurately map the corneal thickness over a wide area, both in normal and opacified eyes. The corneal thickness measurements were highly reproducible. 2. OCT pachymetry based method could detect abnormal corneal thinning in keratoconic eyes. 3.The anterior segment OCT was capable of measure corneal, flap, and stromal bed thickness profiles and maps after LASIK.