In vivo confocal microscopy after photorefractive keratectomy in humans. A prospective, long-term study.

OBJECTIVE: To assess corneal morphological characteristics in vivo after photorefractive keratectomy (PRK) in humans. METHODS: Eighteen eyes were examined before and after PRK by means of in vivo confocal microscopy. Epithelial, stromal, and endothelial morphological characteristics were recorded. Minimum follow-up was 12 months. RESULTS: Immediately after PRK, the anterior stroma showed marked intercellular edema. At 1 month, fine linear structures were noted in the anterior stroma and midstroma, and a thin hyperreflective scar was present. The linear structures and the scar tissue were more marked at 4 months but were still present up to 26 months. Anterior stromal keratocyte density increased significantly 1 and 4 months after PRK, whereas midstromal and posterior keratocytes and endothelial cell densities did not change. Basal epithelial nerves were recognizable as early as 1 month after PRK. Contact lens-related microdots in the stroma remained unaffected. CONCLUSIONS: The stromal linear structures represent a finding that is detectable only by confocal microscopy at high magnification, is not related to previous contact lens wear, and is still visible 26 months after PRK. The extension of these structures as far as the midstroma indicates that the permanent corneal changes caused by PRK affect deeper stromal layers than the immediate subepithelial region.

[Quantification of intrastromal micro-deposits in long-term contact lens patients]. / Quantifizierung intrastromaler Mikroablagerungen bei Langzeitträgern von Kontaktlinsen.

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.