Abstract
Abstract: :
Purpose: A new instrument that performs ultrahigh–resolution full–field optical coherence tomography (OCT) has been used to examine ocular tissues in vitro in rat and porcine eyes. Methods: Our OCT system is based on a Linnik–type microscope, i.e. a Michelson interferometer with identical microscope objectives in both arms, illuminated by a tungsten halogen source. A high resolution CCD camera records a series of interferometric images which are combined to display en face tomographic images in real time. The full–field illumination associated with the two–dimensional detector array avoids the transverse scanning required in traditional OCT systems. This permits the use of high numerical aperture (NA) microscope objectives, which improve the transverse resolution of the instrument. The spatial resolution of our instrument is 0.7 µm × 0.9 µm (axial × transverse). The sample is scanned in the depth direction to obtain a three dimensional (3D) data set, from which sections or movies in any orientation can be displayed. Tissues were extracted from the whole eye and imaged individually. Results: Images of the cornea, crystalline lens, and retina are shown. The unprecedented resolution of our instrument allows better visualisation of ocular tissue structure than any other OCT system. In particular, the visualisation of the layer structure of the cornea and the fibre organisation in the crystalline lens is made possible with our instrument. In the retina, cellular resolution is achieved in the ganglion cell and nerve fibre layers, and the external limiting membrane stands out very clearly. Conclusions: The high resolution of our instrument allows imaging at the cellular level, showing not only differences in texture or tone of tissue but making cellular and fibre structures within tissue layers clearly visible. Images comparable to histology are therefore obtained, but in a non–invasive, non–destructive manner. The use of a simple thermal light source, and the en face nature of image capture, makes the instrument robust and reliable compared to femtosecond laser scanning OCT. For in vitro examination, our instrument offers the best resolution available in OCT.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • cornea: basic science • retina