Effect of Intraoperative Corneal Stromal Pocket Irrigation in Small Incision Lenticule Extraction

Abstract

This study aimed at evaluating the effect of intraoperative corneal pocket irrigation in small incision lenticule extraction (SMILE) and compares it to that in femtosecond laser-assisted in situ keratomileusis (FS-LASIK). Sixteen rabbit eyes underwent a SMILE procedure, with 8 eyes having corneal pocket irrigation, while the other 8 eyes were without irrigation. Another 16 eyes underwent a FS-LASIK procedure for comparison, with 8 eyes having flap irrigation, while the other 8 eyes were without irrigation. The results showed that the changes in the total corneal thickness, anterior and posterior lamellar thickness, measured by the anterior segment optical coherence tomography, were comparable between the SMILE with and without irrigation groups, suggesting that the irrigation did not lead to significant changes in the corneal thickness. However, at postoperative 8 hours, in vivo confocal microscopy showed that the interface reflectivity in the SMILE with irrigation group was significantly higher than that in other three groups. The presence of interface fluid was further confirmed by the identification of fluid pockets with undulated collagen shown on histological section in the post-SMILE with irrigation eyes. Our findings might contribute to the occurrence of post-SMILE delayed immediate visual quality recovery and further clinical study is required.

Figure 1

Representative raster line ASOCT images at 24 hours postoperatively for eyes which underwent (a) SMILE with irrigation, (b) SMILE without irrigation, (c) LASIK with irrigation, and (d) LASIK without irrigation procedure. An increase in the reflectivity could be seen at the cap interface in the post-SMILE eyes (arrowheads) or at the flap interface in the post-FS-LASIK eyes (arrow), and the total corneal thickness and anterior lamellar thickness were accordingly measured. The posterior lamellar thickness was then calculated by subtracting the anterior lamellar thickness from total corneal thickness.

Figure 2

Line graphs showing the mean percentage changes in the (a) total corneal thickness, (b) anterior lamellar thickness, and (c) posterior lamellar thickness at different time points for different groups. 0 hr^∗ indicates immediately after surgery. Error bars represent standard deviations (SD). The mean ± SD values for different groups at different time points were shown (%). The LASIK group had a significantly greater increase in the total corneal thickness and anterior lamellar and posterior lamellar thickness compared to the SMILE with irrigation and without irrigation groups immediately after surgery. The P level indicates the significance level when comparing the LASIK group (with irrigation and without irrigation) with other groups: ^∗∗∗ P < 0.001 and ^∗∗ P < 0.01.

Figure 3

Representative in vivo confocal images at the extracted lenticule plane (SMILE with and without irrigation groups) and at the flap interface (LASIK with and without irrigation groups) at different time points. These interface layers were acellular and were characterized by light-scattering particles. Inset images showed the plane adjacent to the extracted lenticule plane or flap interface. Highly reflective keratocytes were observed in these planes.

Figure 4

Line graph showing the relative intensity of reflectivity for different groups at different time points. At postoperative 8 hours, the SMILE with irrigation group had significantly higher reflectivity than the other three groups. 0 hr^∗ indicates immediately after the surgery. The P level indicates the significance level when comparing the SMILE with irrigation group with other groups: ^∗ P < 0.05 and ^∗∗ P < 0.01. Error bars represent SD.

Figure 5

Histological section with H&E staining for the central corneas of the (a) SMILE with irrigation, (b) SMILE without irrigation, (c) LASIK with irrigation, and (d) LASIK without irrigation groups at 24 hours. In the SMILE with irrigation group, undulated but undisrupted stromal collagen bundles and apparent fluid pockets along the extracted lenticule plane were observed (arrows). Small fluid retention pockets were also observed at the interface in the post-LASIK eyes but less prominent (arrowheads). Original magnification: 200x. Scale bar: 50 μm.