Protective Effects of Deswelling on Stromal Collagen Denaturation After a Corneal Femtosecond Laser Cut

PURPOSE: To evaluate the effect of corneal deswelling prior to a microkeratome and femtosecond (fs) laser cut and the impact of the fs laser energy settings on the tissue surface and collagen quality. METHODS: Porcine and human corneas were incubated in THIN-C (deswelled) or EUSOL-C (control) at 4°C for 4 hours. Porcine corneas were cut using a microkeratome or an Intralase fs laser 150 Hz and 0.75 μJ energy. Human corneas were cut using the laser at different energy settings. The tissue thickness was measured using Visante OCT and the endothelial cell density (ECD) was evaluated by an Eye Bank KeratoAnalyzer or trypan blue staining. The tissue was analyzed using scanning electron microscopy (SEM). RESULTS: In porcine corneas, tissue deswelling resulted in a reduction of 14% in the central corneal thickness (CCT), a regular surface, and increased tissue stiffness without affecting ECD. After fs laser cutting, the control corneas showed superficial collagen denaturation that was absent in the deswelled corneas. The deswelled human corneas showed a CCT reduction of 20%, better surface smoothness, preserved collagen, and increased stiffness after fs laser cutting at 1.0 to 1.2 μJ, compared with controls. Surface smoothness decreased and collagen fibers showed a melted-like aspect both in deswelled and control corneas at greater than 1.4 μJ. CONCLUSIONS: Fs laser cutting parameters can reduce corneal surface smoothness and increase collagen melting damage. The use of a deswelling medium resulted in tissues for Descemet stripping automated endothelial keratoplasty (DSAEK) with increased stiffness, smooth surfaces, and no thermal damage to the collagen matrix.