Efficacy and safety of intracorneal allogenic ring segment implantation in keratoconus: 1-year results

Long-Term Results of Sterile Corneal Allograft Ring Segments Implantation in Keratoconus Treatment

PURPOSE

To evaluate the efficacy and safety of sterile corneal allograft ring segments implantation for the treatment of keratoconus by analyzing long-term visual, refractive, and tomographic clinical outcomes.

METHODS

This prospective study included 62 eyes of 49 patients with keratoconus who underwent corneal allograft ring segments implantation at Istanbul Medipol University Faculty of Medicine between February 2020 and August 2022. Surgical outcomes using the Istanbul nomogram were evaluated in patients preoperatively and postoperatively at 1 month, 6 months, 1 year, and 3 years. Outcomes measured were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical equivalent (SE), spherical refraction (SR), cylindrical refraction (CR), topographic keratometric values, and corneal thickness at the thinnest point.

RESULTS

Preoperative mean UDVA and CDVA (LogMAR) were 0.96 ± 0.50 and 0.72 ± 0.47, respectively, and increased to 0.41 ± 0.34 and 0.22 ± 0.19 at the last visit (P < 0.001). There was a significant decrease in SE, SR, and keratometric values postoperatively (P < 0.001). There was no difference in CR and thinnest corneal thickness values (P = 0.333 and 0.154, respectively). The stromal and epithelial thicknesses measured by anterior segment optical coherence tomography were stabilized at 6 months and 1 year, respectively. No major complications or side effects were observed intraoperatively or postoperatively.

CONCLUSIONS

This study demonstrated that sterile corneal allograft ring segments implantation is a safe and feasible treatment for keratoconus, yielding notable long-term visual outcomes with minimal implant-related complications.

Bowman Layer Marking for Correct Placement of Corneal Allogeneic Intrastromal Ring Segments

ABSTRACT

Corneal allogeneic intrastromal ring segments (CAIRS) refer to the placement of allogeneic rings and segments in intrastromal channels within the cornea. Currently, a deepithelialized donor cornea is used as the allogeneic source for CAIRS and the cut ring is turned sideways and implanted so that the thickness can be varied by varying the distance between the concentric trephine blades. In addition, to obtain a greater effect, CAIRSs are preferred to be implanted with the Bowman layer (BL) facing the corneal apex and posterior stroma facing limbally. Being flexible tissue, it is, however, important to prevent twisting and to maintain correct orientation. We describe a simple technique of marking the BL with a gentian violet surgical marker to simplify CAIRS insertion. BL marking allows easy visibility of twists and helps identify improper orientation, thus allowing correct insertion of CAIRS.

Refractive surgical correction and treatment of keratoconus

Keratoconus is an ectatic corneal disorder that causes severe vision loss. Surgical options allow us to correct, partially or totally, the induced refractive error. Intracorneal ring segments (ICRS) implantation represents a minimally invasive surgical option that improves visual acuity, with a high success rate and a low overall complication rate. Corneal allogenic ICRS consists of ring segments derived from allogenic eye bank-processed donor corneas. Selective topography-guided transepithelial photorefractive or phototherapeutic keratectomy combined with CXL is another way in selected cases to improve spectacles corrected distance visual acuity. The microphotoablative remodeling of the central corneal profile is generally planned by optimizing the optical zones and minimizing tissue consumption. Phakic intraocular lens (PIOL) implant is considered in patients with stable disease and acceptable anatomical requirements. The two types of pIOLs, depending on their implantation inside the eye, are anterior chamber-pIOLs, which fixate to the anterior surface of the iris by using a polymethomethacrolate claw at the two haptics, and posterior chamber-pIOLs. In patients with both cataracts and keratoconus, the correct IOL power is difficult to obtain due to the irregular corneal shape and K values. Toric IOL is recommended, but carefully judging the topography and the possible need of subsequent keratoplasties.