System and method for the non-contacting measurements of the eye

Abstract

Combined equipment for non-contacting determination of axial length (AL), anterior chamber depth (VKT) and corneal curvature (HHK) of the eye, are also important for the selection of the intraocular lens IOL to be implanted, particularly the selection of an intraocular lens (IOL) to be implanted, preferably with fixation of the eye by means of a fixating lamp and/or illumination through light sources grouped eccentrically about the observation axis.

1 . An arrangement for determining the anterior chamber depth of an eye, comprising:
 a) a slit-shaped illumination radiating on the eye at an angle to the observation axis, and imaging optics and comprising at least one light source or LED;   b) a receiver arrangement which detects scatter images coming from structures of the eye located substantially on the observation axis, the receiver arrangement, the slit shaped illumination and the imaging optics being angularly fixed relative to each other;   c) a signal processing device which receives signals from the receiver arrangement and processes the signals to determine distances between portions of the scatter images that represent the structures of the eye and calculates anterior chamber depth from the distances; and   d) a fixating light source emitting a fixating light on which the patient fixes his gaze, the fixating light being coupled along the observation axis, wherein the observation axis substantially coincides with the patient's viewing axis.   
   
   
       2 . The arrangement according to  claim 1 , wherein the angle to the observation axis under which angle the slit-shaped illumination radiates on the eye is fixed, preferably at 33 degree. 
   
   
       3 . The arrangement according to  claim 1 , wherein a slit is arranged after the light sources or LEDs in the illumination direction. 
   
   
       4 . The arrangement according to  claim 1 , wherein imaging optics are constructed anamorphotically or include a cylindrical lens. 
   
   
       5 . The arrangement according to  claim 1 , wherein the receiver arrangement comprises a CCD camera. 
   
   
       6 . The arrangement according to  claim 1 , in which the slit-shaped illumination comprises a series of white light LEDs. 
   
   
       7 . A method for determining the anterior chamber depth of a human eye, comprising the steps of:
 illuminating the eye;   imaging relevant image sections on a CCD camera;   switching the illumination on and off so as to be synchronized with image pulses of the CCD camera;   recording a bright image of the CCD camera when the illumination is switched on and recording a dark image of the CCD camera when the illumination is switched off;   subtracting successive bright images and dark images to generate a differential image to suppress noise;   illuminating the eye by a slit image;   detecting the eye pupil and a fixation point within the pupil in the dark image;   determining an edge shape of scatter images of the slit-image illumination in the differential image;   determining a distance X from the edges of a cornea scatter image and a lens scatter image; and   calculating the anterior chamber depth from the distance X.   
   
   
       8 . The method of  claim 7 , wherein the generation of the differential image comprises further noise suppression by means of median filtering. 
   
   
       9 . The method of  claim 7 , wherein the determination of the edge shape comprises a histogram-based selection of a threshold value for image binarization. 
   
   
       10 . The method of  claim 7 , wherein the determination of the edge shape further comprises rough detection of the edges as such locations where a threshold value is exceeded in a given region around the fixating point. 
   
   
       11 . The method of  claim 10 , wherein the determination of the edge shape additionally comprises fine detection of the edges as such locations where a reversal point of a gray value shape in a line profile which is next to the roughly detected position occurs. 
   
   
       12 . The method of  claim 7 , wherein the determination of the edge shape further comprises elimination of reflections by detecting of maverick or freak values in the edge shape. 
   
   
       13 . A device arrangement which determines the axial length and corneal curvature radius of a human eye, comprising a controller which carries out a central control of adjustable units and optical elements of the device arrangement and calculates the optical action of an intraocular lens to be implanted in the eye. 
   
   
       14 . The device arrangement according to  claim 13 , with a device storage in which calculation formulas are stored such that they can be called up. 
   
   
       15 . The device arrangement according to  claim 13 , which additionally determines anterior chamber depth. 
   
   
       16 . The device arrangement according to  claim 15 , which initially determines the axial length, then determines the corneal curvature radius and then the anterior chamber depth, or which initially determines the corneal curvature radius, then the anterior chamber depth and then the axial length, or which initially determines the corneal curvature radius, then the axial length and then the anterior chamber depth.