Does tissue temperature influence pseudomembrane formation after excimer laser ablation of the cornea

Purpose. To assess the influence of different temperatures of corneal tissue on pseudomembrane formation during excimer laser ablation. Method. 20 human eye bank corneas were adjusted to five different temperatures (n=4): frozen, 4°C, 22°C, 33°C, 50°C, confirmed by infrared pyrometry before and after phototherapeutic keratectomy with VISX 20/20 excimer laser (6 mm diameter, 160 mJ/cm²). After manual removal of the epithelium, 60 microns deep stromal ablation was performed with the corneoscleral button fixed in an artificial chamber. Immediately after the treatment, corneas were fixed in half strength Karnovsky solution and processed for transmission electron microscopic (TEM) examination. The thickness of the electron-dense condensate (pseudomembrane) was measured in the central and paracentral 1 mm and 2 mm of the cornea. Result. The electron-dense condensate (pseudomembrane) did not vary significantly from the central to the peripheral of the ablation, but the membrane showed a tendency to become thinner with the decrease in temperature; 166.4 ± 27.5 nm at a temperature of 4°C, 242 ± 21.1 nm at 33°C, 323.5 ± 29.8 nm at 50°C. The underlying stroma tissue had no prominent changes. Conclusion. Reduction of temperature during excimer laser ablation decreased pseudomembrane formation. Whether this findings can positively influence the degree of haze after excimer laser keratectomy has to be proved in an in vivo study.