First results of in vivo visualization of corneal structures with a modified HEIDELBERG RETINA TOMOGRAPH (HRT) by adapting a computer controlled objective device
J. Stave, R. Guthoff, G. Zinser
Purpose: Our aim was to find out whether it is possible to change the HEIDELBERG RETINA TOMOGRAPH (HRT) from Heidelberg Engineering GmbH (Germany) into a confocal laser scanning microscope by adapting a computer controlled scanning-objective device for the in vivo visualization of anterior segments of the eye. During the computer controlled shift of the focus plane through the cornea the axial scanning images sequences will be used to automated quantification of keratocyte density and three dimensional reconstruction of all corneal structures by using a special software.
Methods: The HRT was extended with an additioanal computer controlled hydraulic linear scanning device (HaSoTec/ FG 30, NIKON hydraulic micromanipulator) in combination with a water contact objective (Zeiss, 40x 0.65 ) in order to focus the laser beam of the HRT onto anterior segments of the eye. In a separate computer the sequence of scanning images of the HRT were recorded and saved. The digital off-line analysis was performed using the software HaSoTec-CHEMOTAXIS. By combining different objectives and zoom-optics it was possible to alter the magnification by a factor up to 1000.
Results: First experiments has been shown, that it is possible to depict all corneal structures with the modified tomograph without loss of the original HRT-function. Primarily we examined in vitro pig and human corneas and in vivo corneas from healthy probands with encouraging results. The illumnation uniformity of the scanned area in the cornea has been improved in comparison with the as so called "flying slit technique" in the most of confocal scanning microscopes.
Conclusion: This microscope provides a new real time imaging technique with high contrast and resolution in non-contact and contact procedures for the qualitative and quantitative in vivo examination of thin layers and structures of the cornea for example before and after LASIK.
Prof. Dr. rer. nat. habil. J. Stave, Dept. of. Ophthalmology University of Rostock, Doberaner Str. 140, D-18055 Rostock