Corneal densitometry changes in keratoconus patients after intrastromal corneal ring segments implantation

Keratoconus (KC) is an ectatic corneal disorder characterized by progressive corneal thinning with myopic astigmatism. Intrastromal corneal ring segments (ICRS) have been broadly selected as a surgical intervention for KC correction to delay the need of keratoplasty. The purpose of this study was to evaluate the corneal densitometry changes in the various annuluses and depths in KC corneas after intrastromal corneal ring segment (ICRS) implantation and to correlate those changes with the other optical and refractive outcomes. This was a prospective interventional study included 56 eyes of 40 patients with KC who underwent femtosecond laser-assisted Keraring ICRS implantation. The uncorrected and best-corrected visual acuities (UCVA and BCVA), refraction, keratometry, Q-value, thinnest corneal location thickness (TCLT), and corneal densitometry in all the annular zones were assessed preoperatively and 90 days after surgery. Following the ICRS implantation after 3 months, when compared to preoperatively, the UCVA, BCVA, improved significantly from 0.21±0.12 and 0.44±0.15 to 0.27±0.12 and 0.58±0.15 (P<0.001) and spherical equivalent (SE) decreased significantly, from −5.28±1.65 D to −4.05±1.24 D (P<0.001) whereas the K1, K2, Km, Kmax, reduced significantly from 47.67±4.10 D, 51.39±4.74 D, 49.44±4.28 D, and 57.78±7.35 D, to 44.28±2.86 D, 46.84±3.42 D, 45.45±2.98 D, and 53.89±5.49 D (P<0.001) respectively. Corneal astigmatism, and Q-value were markedly improved from 3.73±2.17 D and −0.99±0.5 to 2.55±2.08 and −0.28±0.5 (P<0.001) .As regard corneal densitometry there was a significant elevation in the mean density of 2–6 mm annulus for the anterior and posterior layers (P=0.001), of 2–6 mm and 6–10 mm annuluses and total diameter for the central layer (P<0.001, P=0.047, and P<0.001, respectively), and of 2–6 mm annulus and total diameter for the total corneal thickness (P<0.001 and P=0.014, respectively). In contrast, a significant decline in the densitometry readings was observed in the 10–12 annulus for the central, posterior, and total corneal layers (P=0.003, P<0.001, and P=0.008, respectively). The percentage changes in the corneal densitometry readings did not significantly correlate with the percentage changes in the UCVA, BCVA, SE, CA and Q value. The percentage changes in the central and total 2–6 mm annuluses densities correlated negatively with the percentage changes in the K1 (r=−0.30, P=0.025 and r=−0.29, P=0.029, respectively), K2 (r=−0.33, P=0.013 and r=−0.31, P=0.021, respectively), and Km (r=−0.34, P=0.010 and r=−0.33, P=0.014, respectively). The ICRS implantation results in significant changes in corneal densitometry specifically in the central corneal layer and in the 2–6 mm annulus, with an inverse correlation with keratometric values of the front corneal surface. Besides, ICRS leads to substantial improvements of refractive status, visual acuity and corneal keratometry and asphericity.