[Modified Heidelberg Retinal Tomograph HRT. Initial results of in vivo presentation of corneal structures]

Abstract

Background: At present, confocal tandem scanning microscopes with halogen or mercury lamps are used to depict all corneal structures in vivo, e.g., before and after PRK or LASIK. Insufficient imaging quality and irregular corneal illumination are the main problems for automatic quantitative evaluation of the keratocyte density when applying this instrument. A high correction is required for correcting the background irregularities of pictures. Our aim was to find out whether it is possible to change the Heidelberg retina tomograph (HRT) into a high-resolution digital laser scanning microscope for the visualization of anterior segments of the eye, coupled with a special evaluation software.

Material and method: We developed a lens adapter for the HRT that focusses the laser beam onto the cornea by combining with an external, computer-controlled hydraulic z-scan sledge. By using a programmable adaptation for the external stepmotor on the z-scan sledge in combination with all internal control functions and patient data, it is possible to create a digital confocal laser scanning microscope with retention of all the original HRT functions. For evaluation of the corneal images and automatic count of keratocytes, we used special 3D and Chemotaxis software.

Results: First investigations show a regular illumination of all corneal structures as the epithelium, endothelium, and keratocytes. The hydraulic z-scan allowed a precise shift of the focus through the cornea to take series of images for the evaluation of the keratocyte profile and 3D reconstruction of all corneal structures.