Laser method for corneal structure investigation

Military Hospital, Clinic ofOphthaimoiogy, BucharestABSTRACTThis paper reports a laser method for corneal structure investigation which allows to obtain images of corneallayers as well as information about dimensions of the endothelium and basal epitheliuin cells. The method's principle isbased on the laser radiation reflection at the interface between ocular media having different refractive indices. So, thelaser incident beam on the cornea is multiply reflected and refracted within it, since the cornea is a superposition of severaltransparent layers with different refractive indices. Ifobserved on a screen, the radiation reflected by a certain corneal layerforms on it the image of corneal cell structure. Because of cornea curvature, the reflected beam which contains informationabout corneal structure- becomes strongly divergent; therefore the experimental setup forms the cell images big enough tobe seen directly by eye.There were used both a HeNe (632.8 nm) and a M (488.5 14 mu) lasers at a power level less than 0. 1 mW. Thereflected beam, strongly divergent because of the corneal curvature of the rabbit eye, allows to obtain the cornea! cellimages on a screen mounted at a variable distance with respect to the eye. The observed images were recorded eitherphotographically or using a video-camera.The reflection corresponding to epithelium and endothelium leads to a superposition of images originated in thesetwo corneal layers. In the central zones ofthe images, the epithelial cells prevail, showing a less regular structure. Towardsthe peripheral zone of the image, the endothelial cells replace the epithelial ones, but the intracellular membrane may beseen less intense.Using a model of image fonnation which takes into account the optical phenomena appearing within the cornea,we have calculated the magnification factor of the system, and finally, the typical values of 35 im for endothelial cell