Graft profile and thickness as a function of cut transition speed in Descemet-stripping automated endothelial keratoplasty.

PURPOSE: To determine the profile of endothelial keratoplasty lenticules prepared using a microkeratome and evaluate the impact of varying cut transition speed on cut depth and profile using anterior segment optical coherence tomography (AS-OCT). SETTING: Department of Cornea and External Diseases, Moorfields Eye Hospital, London. United Kingdom. DESIGN: Experimental study. METHODS: Fourier-domain AS-OCT was used to image 25 corneal specimens before and after microkeratome dissection with a 350 µm head. A pilot series of 7 corneas were cut and imaged with the following 18 corneas divided into regular cut transition speed and slow cut transition speed groups (9 in each). Proximal, central, and distal precut corneal thickness and post-cut residual bed thickness were measured using the integrated caliper tools of the Fourier-domain AS-OCT device. Cut depth was calculated by subtraction. RESULTS: The slower microkeratome pass speed produced significantly thinner donor lenticules (mean 148 ± 45 µm [SD]) than the standard pass speed (mean 234 ± 35 µm) (P ≤.0001). In both groups, significant asymmetry was observed in donor lenticules with a deeper cut depth and a thinner lenticule at the beginning of the microkeratome pass (proximal stromal bed). The mean difference between the proximal and distal stromal bed thickness was 61 ± 63 µm in the standard group and 52 ± 22 µm in the slow-pass group (P=.159). CONCLUSIONS: Reducing the transition speed in microkeratome dissection produced thinner donor lenticules. Thickness asymmetry is an inherent flaw with current microkeratome dissection that cannot be easily corrected by altering preparation technique.

Theoretical, experimental, and optical coherence tomography (OCT) studies of graft apposition and adhesion in Descemets stripping automated endothelial keratoplasty (DSAEK).

PURPOSE: To investigate the effects of adhesion promoting surgical adjuncts in Descemets stripping automated endothelial keratoplasty (DSAEK). The effects of air-fill pressure, duration, use of venting incisions and stromal roughening on fluid dispersion, and donor adhesion strength were examined in theoretical, optical coherence tomography (OCT), and strain gauge models of DSAEK. METHODS: OCT analysis: DSAEK modeled using a microkeratome prepared lenticule inserted under a "recipient" corneo-scleral rim mounted on an artificial anterior chamber. Pressure of 18 mm Hg (n = 6) or 60 mm Hg (n = 6) was applied. The area of interface fluid was measured sequentially. The area of interface fluid before and after opening of venting incisions was measured (n = 6). Adhesion experiments: Direct measurement of adhesion force using a universal testing machine was performed. Peak adhesion after compression at 60 mm Hg/8 minutes, 60 mm Hg/1 minutes, 18 mm Hg/8 minutes, and 18 mm Hg/1 minutes (n = 8 each group) was measured. Subsequently, adhesion after complete removal of interface fluid and after stromal roughening was measured in separate samples (n = 12). RESULTS: Interface fluid diminishes with time during tamponade at both low and high pressures (P < 0.0001). Pressure had no effect on amount or rate of fluid dispersion. Venting incisions eliminated interface fluid in all samples when opened sufficiently. Adhesion is independent of anterior chamber air tamponade pressure (P = 0.38). Complete removal of interface fluid increases average adhesion (16.0 mN vs. 7.8 mN, P = 0.0001). Roughening of the host stroma increased adhesion (13.8 mN vs. 9.8 mN, P = 0.0034). CONCLUSIONS: Venting incisions and stromal roughening aid adhesion in DSAEK. Sustained high-pressure anterior chamber air tamponade has no demonstrable effect on measured fluid dispersion or adhesion strength.