Quality of corneal lamellar cuts quantified using atomic force microscopy

PURPOSE: To quantify the cut quality of lamellar dissections made with the femtosecond laser using atomic force microscopy (AFM). SETTING: Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA. DESIGN: Experimental study. METHODS: Experiments were performed on 3 pairs of human cadaver eyes. The cornea was thinned to physiologic levels by placing the globe, cornea side down, in 25% dextran for 24 hours. The eyes were reinflated to normal pressures by injecting a balanced salt solution into the vitreous cavity. The eyes were placed in a holder, the epithelium was removed, and the eyes were cut with a Visumax femtosecond laser. The energy level was 180 nJ for the right eye and 340 nJ for the left eye of each pair. The cut depths were 200 mu m, 300 mu m, and 400 mu m, with the cut depth maintained for both eyes of each pair. A 12.0 mm trephination was then performed. The anterior portion of the lamellar surface was placed in a balanced salt solution and imaged with AFM. As a control, the posterior surface was placed in 2% formalin and imaged with environmental scanning electron microscopy (SEM). Four quantitative parameters (root-mean-square deviation, average deviation, skewness, kurtosis) were calculated from the AFM images. RESULTS: From AFM, the 300 mu m low-energy cuts were the smoothest. Similar results were seen qualitatively in the environmental SEM images. CONCLUSION: Atomic force microscopy provided quantitative information on the quality of lamellar dissections made using a femtosecond laser, which is useful in optimizing patient outcomes in refractive and lamellar keratoplasty surgeries. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2013; 39:110-117 (C) 2012 ASCRS and ESCRS