Ray Tracing Illustrated

1) The iTrace system projects a thin laser beam through the entrance pupil parallel to the eye’s line of sight. 

2) The location where this beam strikes the retina is measured by capturing the exiting scattered light and focusing it onto X & Y position sensitive linear arrays. 

Once the iTrace determines the position of point 1, the system moves the laser beam to a new position and determines the location of this point on the retina.  This process continues until 256 separate points have been projected through the entrance pupil, and is completed in 400 milliseconds – faster than the blink of an eye! 

3) The iTrace displays the resulting Retinal Spot Pattern. If the eye were emmetropic, then all 256 points would fall on one spot in the center of the macula. Generally local aberrations in each beam’s path through the cornea and lens cause a shift in the location on the retina. In this example, the pattern is large and broad indicating a myopic eye.

Ray Tracing Advantages

Ray tracing has several key advantages over other technologies.  First the separate, sequential capture of data means that there is no confusion in the analysis between the location of a point in the entrance pupil and the location where that point is observed on the retina.  Therefore highly aberrated eyes are measured easily and accurately with ray tracing technology.  Second, because the pattern of laser spots projected through the entrance pupil is controlled through software, the system can track the pupil size and then project all 256 points into a pupil as small as 2mm or as large as 8mm. Third, since each point is measured separately using linear array detectors, the software’s task of locating the center of each spot is more precise than with Hartmann-Shack or Tscherning technologies.