Quantification of intrastromal micro-dot deposits in the cornea of long-term contact lens wearers

Background Some months ago we described morphological changes in the stroma of the cornea of patients with a history of long term contact lens wear. These degenerations consist of little highly reflective structures called "micro-dots" For a more precise quantification of the micro-dots we established a clinically practicable method for measuring and counting. Material and methods The micro-dots can be visualized in optical sections with the scanning slit confocal microscope. To get the real thickness of a single optical section we had to develop a in vitro model, which consists of a gel of agar with particles of latex of different size. Results Some stereological methods made it possible to calculate the thickness of an optical section as seen with the confocal microscope. We found out that the thickness shows a variation depending on the reflectivity and size of the particles as well as on the aperture of the objective used. From the area of the frame and the thickness of the optical section we could calculate the density of the highly reflective particles. Discussion Up to now we could determine the morphological changes (micro-dots) in the cornea of patients with a history of long term contact lens wear in a semiquantitative manner only. With the presented method we are able to make a quite precise numerical estimation of micro-dots. This is very useful to follow up the progress of these stromal changes over many years.