In vivo imaging of the development of linear and nonlinear retinal laser effects using optical coherence tomography in correlation with histopathological findings

TLDR: A correlation between cross-sectional OCT-images and structural findings using classical histopathological techniques facilitates a better interpretation of the characteristic patterns seen in OCTimages and defines the sensitivity of the OCT-technique to image morphological details.

Abstract: Optical Coherence Tomography (OCT) is a new, non-invasive diagnostic technique for high resolution optical 3D imaging, which was developed and applied to several different biological materials during the lasi; five years [1, 2, 3]. A unique application ofthis technique is the microscopical cross-sectional imaging ofpostenor structures ofthe eye which are not accessable with other high resolution techniques in-vivo neither with x-ray-imaging nor with high frequency ultrasound scanning. The superior spatial resolution on the order ofabout lOtm laterally and axially, the high signal-to-noise ratio ofmore than 100 db and the fast acquisition-time of one second for a two dimensional scan provides a technique for cross-sectional in-vivo-momtoring ofintraocular structures and therefore the possibility to study the time course of anatomical and pathological developments in the eye. The acute morphological changes of ocular structures and their biological healing response after shortterm impacts such as high-intensity laser exposures are ofparticular interest for the understanding of the mechanisms responsible for therapeutic laser-application in ophthal-mology as well as for laser injury to the eye. A correlation between cross-sectional OCT-images and structural findings using classical histopathological techniques facilitates a better interpretation ofthe characteristic patterns seen in OCTimages and defines the sensitivity ofthe OCT-technique to image morphological details. On the other hand preparational artefacts not avoidable in all histological procedures can be identified and analyzed by comparing histological micrographs with OCT-images of exactly the same structure. First results of an experimental study where retinal effects were produced in monkey eyes using laser pulses from 200 ms to 130 fs in duration are presented in this article. The applied energies from 5tJ to 50 mJ were able to induce the whole spectrum of biological effects possible in the eye, ranging from intraretinal microruptures to extensive thermal denaturation and massive preretinal hemorrhages [4, 5, 6].