Anterior segment imaging in vivo in rats and ex vivo in mice using full-field optical coherence tomography

We present results of ex vivo imaging of the mouse cornea following photorefractive keratectomy and in vivo imaging in the anterior segment of the rat eye using full-field optical coherence tomography. The instrument is based on the Linnik interferometer, illuminated by a white light source: a tungsten halogen lamp for ex vivo imaging and a fibered Xenon arc lamp for in vivo imaging. En face tomographic images are obtained in real-time without scanning by calculating the difference of two phase-opposed interferometric images recorded by a CCD or CMOS camera. Spatial resolution of similar to 1 mu m in both axial and lateral directions is achieved thanks to the short coherence length of the illumination source and the use of relatively high numerical aperture microscope objectives. A detection sensitivity of up to 90 dB is reached by means of pixel binning and image averaging. Photorefractive keratectomy was performed on mice and the excised eyes were examined under immersion 21 days after surgery. Rats were anesthetized and their anterior segments imaged under immersion. The high resolution of our instrument gives cellular-level resolution in the cornea, allowing visualization of individual stromal keratocytes and collagen fibers, and cells in the endothelium. The basal and Descemet's membranes are well defined. Quantitative measurement of scattering in each layer is possible. Penetration to the level of the lens surface is achieved. Acquisition of stacks of en face images permits three-dimensional navigation through the cornea. Development of image treatment algorithms to allow three-dimensional reconstruction is discussed. The full-field optical coherence tomography technique could be useful in monitoring corneal scattering following refractive surgery.