PMC4025147_01
a Lasik Xtra: after flap lifting and excimer laser treatment, the corneal stroma is soaked by riboflavin 0.25% saline solution (VibeX Xtra) for 90 s. b After 90 s of riboflavin soaking, the corneal surface is washed with balanced salt solution and the flap repositioned. Then, accelerated high-fluence corneal collagen cross-linking was performed at 30 mW/cm2 for 90 s of UV-A exposure. c The final aspect of the cornea at the end of the treatment is shown.
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F1
The Lasik procedure (fig. 1) was performed by the IntraLaseTM FS Laser (Abbott Medical Optics Inc.,
Confocal microscopy overview in the first week after Lasik Xtra. a Undamaged basal epithelium. b Subepithelial plexus fibers did not disappear after treatment (arrow). c, d Slight keratocyte apoptosis associated with edema into the corneal flap before Lasik interface (arrow). e, f Lasik interface with bright hyperreflective particles (arrows). g Keratocyte apoptosis and increased edema beyond the interface until 150 microm showing the area of maximum photooxidative impact, i.e. maximum riboflavin UV-A-collagen interaction (asterisk). h, i Vertical transition area delimiting the end of photooxidative damage and apoptosis at 160 microm, i.e. riboflavin UV-A interaction (white arrows). j Intermediate stroma unreached by photooxidative damage, i.e. riboflavin UV-A interaction. k Deep stroma unreached by photooxidative damage, i.e. riboflavin UV-A interaction. l Corneal endothelium showing a circular area of pseudo-guttae (arrow).
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F2
The postoperative in vivo micromorphological analysis (fig. 2) revealed the following: the epithelium (fig. 2a) showed slight alterations due to UV-A radiation, demonstrating areas of missing cells in the first 15 days after treatment. Even if subjected to slight damage, the subepithelial fibers did not disappear after Lasik Xtra as shown in a confocal scan (fig. 2b). The stroma beyond the interface demonstrated relevant interactions between UV-A, riboflavin and corneal collagen (fig. 2g) with evident keratocyte apoptosis, documented by rarefaction of keratocyte nuclei and diffuse edema, until a depth of 60 microm over the interface, where the apoptotic phenomena ended, resembling the normal appearance of the stroma shown as well in fig. 2h and i. The intermediate stroma beyond 160 microm and the deep stroma were unreached by the combined photoablative, photodisruptive and photooxidative damage, as documented by the presence of normal keratocyte nuclei (fig. 2j, l). Corneal endothelium examined in the first 15 days after treatment showed an area of missing cells similar to guttae (fig. 2l) suspecting a potential hot-spot area induced by high-intensity UV-A power or related to poor corneal thickness.
Corneal endothelium at 1 (a), 3 (b), 6 (c) months after Lasik Xtra showing cell pleomorphism. No significant endothelial cell loss was established after treatment.
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F3
Indeed no changes in endothelial cell count (2,739 cells/mm2 at the 6th month) were recorded during the follow-up and the endothelium assumed a slight pleomorphic appearance as shown in fig. 3.