Early postoperative changes in corneal densitometry after SMILE with 120-μm and 130-μm cap thickness: a comparative study.

OBJECTIVE

To compare early postoperative changes in corneal densitometry after small incision lenticule extraction using 120-μm and 130-μm cap thicknesses.

METHODS

69 eyes of 39 patients who underwent small incision lenticule extraction (SMILE) with cap thicknesses of 120-μm (n ​= ​34) and 130-μm (n ​= ​35) were included in this study. The corneal densitometry (CD) of three zones (0-2 ​mm, 2-6 ​mm, and 6-10 ​mm) of the anterior, central, and posterior corneal layers was evaluated before, one week, and one month after surgery. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical degree, cylinder degree, and spherical equivalent (SE) were also analyzed and compared between the two groups before and after surgery.

RESULTS

Little difference was detected between the two groups in postoperative UCVA, BCVA, SE, and cylinder degree at one month. No statistically significant differences were found between the preoperative and postoperative CD values for the overall (0-12 ​mm) cornea and the 6-10 ​mm zone in either group. A significant increase in CD was observed in the 0-2 ​mm and 2-6 ​mm zones of the anterior layer in the 120-μm group, and the 0-2 ​mm zone of the central layer in the 130-μm group, one week postoperatively. These changes persisted for one month after surgery ( ​< ​0.05). The CD in the central layer (0-2 ​mm and 2-6 ​mm) in the 120-μm group, as well as the total layer (0-2 ​mm and 2-6 ​mm) in both groups, significantly increased at the first postoperative week but returned to preoperative levels by one month after surgery. Additionally, the CD of the anterior layer (0-2 ​mm and 2-6 ​mm) increased significantly in the first week postoperatively, decreased significantly one month postoperatively, but remained significantly higher than baseline in the 130-μm group. In both groups, the CD of the posterior 0-2 ​mm zone decreased. Moreover, the increase in CD in the anterior 2-6 ​mm zone one week postoperatively was significantly higher in the 120-μm group compared to the 130-μm group (ΔCD 2.4 ​± ​1.55 vs. 1.64 ​± ​0.87, ​= ​0.014). Postoperative corneal wavefront aberrations were significantly higher in the 120-μm group than in the 130-μm group.

CONCLUSIONS

CD increased mainly in the 0-6 ​mm zone of the anterior layer in the early phase after the SMILE procedure with both the 120-μm and 130-μm groups. The increase in CD in the anterior 2-6 ​mm zone one week postoperatively was higher in the 120-μm group than in the 130-μm group. SMILE with 120-μm and 130-μm cap thickness were both efficient and safe, but eyes with a 120-μm cap thickness showed higher postoperative corneal wavefront aberrations.