Intracorneal ring segment implantation for eyes with keratoconus and corneas thinner than 400 microns

Abstract

Background: Intracorneal ring segment (ICRS) implantation is a promising and effective treatment option for keratoconus. However, a corneal thickness of less than 400 microns presents a unique challenge. This study assessed the clinical course and visual outcomes in patients with Amsler–Krumeich stage 2 or greater keratoconus and clear corneas, with a minimal corneal stromal thickness of 350 microns but less than 400 microns in the proposed implantation area, up to 6 months after ICRS implantation.

Methods: This non-randomized, prospective, interventional case series was conducted at a single tertiary center, consecutively recruiting patients with keratoconus scheduled for ICRS implantation who fulfilled the eligibility criteria. Detailed ophthalmological assessments were performed at baseline and 6 months postoperatively, including measurements of uncorrected distance visual acuity (UCDVA), best corrected distance visual acuity (BCDVA), and manifest refraction with documentation of the spherical component of the refractive error (in diopters [D]), cylindrical component of refractive error (in diopter cylinder [DC]), and axis of astigmatism (in degrees). Corneal topographic and pachymetric evaluations were performed using Pentacam HR, including keratometry (K) values in D (flat K or K1, steep K or K2, and mean K or Km), corneal astigmatism in DC, central corneal thickness (CCT), and corneal asphericity coefficient (Q value).

Results: We included nine eyes of nine patients with keratoconus and a mean (standard deviation) age of 33.2 (8.2) years (range: 25–44 years). Five patients were women (56%), and four were men (44%). All eyes experienced a statistically significant improvement in the mean visual and refractive outcomes at the 6-month postoperative visit, including UCDVA, BCDVA, sphere, and cylinder (all P < 0.05). Similarly, we recorded a statistically significant improvement in the mean corneal tomographic and topographic data, including the K1, K2, Km, CCT, and Q values (all P < 0.05). No serious complications occurred for up to 6 months of follow-up. Only one patient complained of night glare, which was successfully treated with pilocarpine 1% eyedrops for 3 months.

Conclusions: ICRS implantation may offer a safe and effective option for selected patients with keratoconus and corneal thickness less than 400 microns, as evidenced by short-term improvements in visual, refractive, topographic, and tomographic parameters. No vision-threatening complications occurred. However, given the case-series study design, limited sample size, and short follow-up period, these findings should be interpreted with caution. Further controlled trials are required to validate these preliminary results.