Atomic force microscopy analysis of normal and photoablated porcine corneas

We showed the capabilities and accuracy of atomic force microscopy (AFM) techniques for imaging and analyzing the corneal epithelium and the photoablated corneal stroma. Eight normal porcine corneas, half of which were ablated using a scanning-spot excimer laser, were examined. All the corneas were imaged in balanced salt solution after fixation in glutaraldehyde. In the normal untreated corneas we observed the epithelial surface showing the typical polygonal cells and presenting numerous microprojections. The superficial epithelial cells were classified in three types as a result of the anterior-surface roughness measurements. AFM images of the photoablated corneal specimens showed undulations and granule-like features on the ablated stromal surface, specific to 193-nm ArF laser irradiation. Nevertheless, the quantitative analysis confirmed the precision of excimer laser surgery in removing sub-micrometric amounts of tissue. AFM showed to be a high-resolved imaging tool for the scanning of both native as well as photoablated corneal specimens. Also, this technique permits precise topographic analysis of the corneal plane, in the nanometric scale, of which smoothness is an important physical characteristic and necessary to achieve an optimal optical quality of the eye.