Refractive errors after PK improve after surface ablation and MMC

Surface excimer laser and application of topical mitomycin C 0.2% results in increased vision when used to treat refractiveerrors after penetrating keratoplasty, said Michael Lawless, FRACO, from the Vision Eye Institute, Chatswood, New SouthWales, Australia.

"The decision making process in refractive surgery after corneal transplantation is different from normal patients," Dr.Lawless stated.

Among the main factors to consider are the viability of the graft itself, endothelial cell count and quality, host disease,the graft hose scar, corneal irregularity, refractive stability, the correlation between refractive and keratometricastigmatism, and the presence of cataract.

He reported the results of surface excimer laser and application of mitomycin C for up to 60 seconds (average, 35 seconds)after corneal transplantation in 44 eyes. Three surgeons performed all the procedures; 29 eyes were treated with oneproprietary laser (LADARVision, Alcon Laboratories) and 15 eyes with another laser (Allegretto, Alcon Laboratories/WaveLight).

Postoperatively, Dr. Lawless reported, that all parameters (sphere, cylinder, spherical equivalent, average K values, andcorneal topography) improved significantly (p = 0.05) at 1 and 3 months.

"There was a trend toward improvement in the best spectacle-corrected visual acuity; however, 10.2% of eyes lost two or morelines of best-corrected visual acuity (BCVA) at 1 month," he said. "At 3 months, 5.8% lost two or more lines of BCVA. Theoverall trend was toward improvement."

The maximum astigmatism that could be corrected was 6 D, but some patients had up to 10 or 12 D, he said. He also reportedthat 25% of eyes achieved 20/20 at 3 months compared with only 10% of eyes preoperatively.

With this procedure, along with the trend toward increased BCVA, regular astigmatism can be more fully corrected and there issome decrease in irregular astigmatism seen.

A comparison of the results of this procedure with LASIK after corneal transplantation indicated that the patients whounderwent the surface excimer laser procedure fared better than patients treated with LASIK.