Corneal densitometry changes after femtosecond laser-assisted intracorneal ring segments implantation in keratoconus

Abstract Background: Intrastromal corneal ring segments are commonly implanted in the corneas of eyes with mild-to-moderate keratoconus; however, changes in corneal densitometry (CD) after implantation are a matter of debate in the current literature. We evaluated the changes in CD ۱ and ۳ months after femtosecond laser-assisted Keraring implantation. Methods: This retrospective, non-comparative, multicenter, case series study included patients with keratoconus who underwent femtosecond laser-assisted implantation of double segments with ۹۰° and ۱۶۰° arc lengths or two ۱۶۰° arc length Keraring segments. Demographic and baseline clinical ophthalmic data were recorded. Corneal topography and tomography data acquired using a Pentacam HR Scheimpflug tomography system (Pentacam High Resolution; Oculus, Wetzlar, Germany) with a best-fit sphere were used as a reference surface. Using the Pentacam HR, CD measurements were acquired over a corneal area of ۱۲ mm in total and at four concentric zones (۰–۲, ۲–۶, ۶–۱۰, and ۱۰–۱۲ mm) of three corneal stromal depths: ۱۲۰ micrometers of the anterior corneal stromal layer, ۶۰ micrometers of the posterior corneal stromal layer, and the central layer of stroma lying between these two layers. Results: We included ۴۰ eyes of ۴۰ patients, including ۸ (۲۰%) male and ۳۲ (۸۰%) female individuals, with a mean (standard deviation) age of ۲۱.۰ (۶.۴) years. We observed a significant improvement in the topographic values of steep keratometry (K), flat K, maximum K, and corneal astigmatism (all P < ۰.۰۵), but not in the mean K, thinnest corneal pachymetry, corneal thickness at the apex, back elevation, or front elevation (all P > ۰.۰۵). The mean total anterior, central, and posterior CD differed significantly among the time points, with a significant increase from the preoperative to the ۱-month and ۳-month postoperative visits (all P < ۰.۰۵) and no difference between those of the ۱-month and ۳-month postoperative visits (all P > ۰.۰۵). The mean CD for the anterior layer in the central, paracentral, and mid-peripheral zones, and the central layer in all four zones, differed significantly among time points, with a significant increase from the preoperative to the ۱-month and ۳-month postoperative visits (all P < ۰.۰۵), which remained unchanged from the ۱-month to the ۳-month postoperative visit (all P < ۰.۰۵), except for the central ۲–۶-mm zone, which decreased significantly from the ۱-month to the ۳-month postoperative visit (P < ۰.۰۰۱). The CD of the central ۱۰–۱۲-mm zone did not differ significantly in each pairwise comparison (all P > ۰.۰۵). In contrast, CD for the posterior layer in the paracentral zone decreased significantly from the preoperative to the ۱-month and ۳-month postoperative visits but increased, to a lesser extent, from the ۱-month to the ۳-month postoperative visit (all P < ۰.۰۵). Conclusions: Femtosecond laser-assisted Keraring implantation significantly changes CD, with improvement in most topography parameters. Further longitudinal studies with larger sample sizes are required to verify these preliminary findings.