SURFACE QUALITY OF EXCIMER-LASER CORNEAL ABLATION WITH DIFFERENT FREQUENCIES

To test the effects of different frequencies of a 193-nm excimer laser on the surface smoothness of the ablated materials and the damage to the adjacent structure, four different frequencies (5, 10, 15, and 20 Hz) of a 193-nm excimer laser were used to perform ablations on 20 rab bit corneas and four polymethylmethacrylate blocks at a fluence of 160 mJ/cm2. Each frequency was tested five times on five corneas. The abl ated materials were processed and examined with scanning electron micr oscopy (SEM) and light and transmission electron microscopy (TEM) and a Zygo interference microscope, which quantitatively evaluates the sur face smoothness. The results from the Zygo microscope show that there is no statistically significant difference in surface smoothness betwe en any two different frequencies. The SEM reveals similar regularity a nd uniformity on the ablated surfaces, with no relationship between th e laser frequencies and the amount of surface deposits. The TEM demons trates no correlation between the various frequencies and the thicknes s of the superficial pseudomembrane and the amount of collateral damag e in the adjacent stroma. It appears that the higher frequencies are c omparable to the lower one (5 Hz) as to ablation quality, with the ben efit of curtailing surgical time and decreasing the chances of eye mov ement.