Clinical And Corneal Topographic Outcomes Of Cornea Allograft Ring Segment (Keranatural) Implantation In Keratoconus: Visual, Optical, And Epithelial Remodeling Effect

The purpose of this study is to evaluate the anatomical and functional outcomes of corneal allograft ring segment (KeraNatural, VisionGift, Portland, OR) implantation in patients with keratoconus.Specifically, this study aims to assess changes in epithelial thickness distribution, corneal topography, visual acuity, and wavefront aberrations before and after surgery. By analyzing these parameters, we seek to determine the effectiveness of Keranatural graft implantation in improving corneal structure, enhancing visual function, and potentially delaying the need for more invasive surgical treatments, such as keratoplasty. 

This retrospevtive study conducted at Swiss Vision Clinic in Istanbul, Türkiye. All patients were operated on by the same surgeon, Dr. Aylin Kilic. All measurements were performed using the CSO MS-39 AS-OCT/Placido topographer (CSO, Florence, Italy).

This study included patients with keratoconus who underwent KeraNatural implantation between January 2023 and July 2024. Preoperative and postoperative assessments included visual acuity, slit-lamp biomicroscopy, and fundus examination. Visual acuity was recorded in Snellen and converted to LogMAR for analysis. With MS-39, the following parameters were measured: K1, K2, Kmean, Kmax, CCT (6 mm), ACD, corneal volume (10 mm), S-I and CS-I indices (anterior/posterior), corneal and epithelial wavefront aberrations (OPD, HOA, astigmatism, coma, spherical, residual aberrations at 4.0 mm), and epithelial thickness mapping (central 3.0 mm and quadrants at 3.0–6.0 mm).

A total of 28 eyes from 21 patients (18 males, 3 females) were included, with a mean age of 30.89 ± 6.96 years. The mean follow-up was 18.81 ± 4.21 weeks. Visual and refractive outcomes improved significantly, with UDVA improving from 1.14±0.64 to 0.30±0.27 LogMAR (p<0.001). K1 (ranging from 49.1 ± 6.19 D to 45.3 ± 6.85 D) and K2 (ranging from 53.5 ± 7.51 D to 49.3 ± 7.84 D decreased significantly. However, Kmax remained unchanged (p=0.115). Cornea coma aberration significantly decreased, while spherical aberration increased (p<0.05). Additionally, total and central maximum epithelial thickness significantly increased, particularly in the nasal, inferior, and temporal quadrants(p<0.001).

In conclusion, Keranatural allograft implantation significantly improves both visual acuity and corneal topography in keratoconus patients, with positive changes in corneal wavefront aberrations. The procedure promotes corneal reshaping, contributing to enhanced visual quality, and provides new insights into epithelial thickening and compensatory changes. These findings highlight Keranatural implantation as a promising treatment option for keratoconus, offering both structural and functional benefits. However, further studies with larger sample sizes and longer follow-up periods are necessary to confirm these results and better understand long-term outcomes and graft integration.