The Epithelial Remodeling After Corneal Allogenic Intrastromal Ring Segment Implantation

Corneal allogenic intrastromal ring segment (CAIRS) implantation is a recent alternative method before penetrating keratoplasty for keratoconus patients. We aimed to assess the corneal pachymetry and related corneal wavefront changes in different optical zones as a compensatory process after CAIRS implantation.

Single-center, cross-sectional clinical study.

Keratoconus patients who received CAIRS at least 12 months ago were included in the study. Corneal tunnels were fashioned using a femtosecond laser with an inner and outer diameter of 4.5 mm and 7.00 mm, respectively. The corneal and epithelial thickness with aberrations were evaluated with a recent corneal tomography device (MS-39, CSO, Italy). All pachymetry measurements were taken in two different selected zones. Zone 1 was determined as a circle with a radius from the center of the cornea to the thickest point of the epithelium.  Zone 2 was determined as a circle with a radius from the center of the cornea to the thickest point of the cornea. The epithelial and corneal wavefront coefficients were analyzed in 4 mm and 6 mm optical zones.

Mean zone 1 diameter was 4.36 ± 08.19 mm and was close to the inner border of the intrastromal tunnel. Mean zone 2 diameter was 6.73 ± 1.12 mm. Mean epithelial thickness was 76.64 ± 6.13 µm in zone 1 and was decreased to 46.98 ± 4.02 µm in zone 2. Mean corneal thickness was 535.15 ± 36.45 µm in zone 1 and increased to 911.49 ± 68.2 µm in zone 2 (p <0.001). A negative correlation was found between epithelial thickness and corneal thickness in zone 2 (r = -0.734). At 4 mm, mean epithelial optical path difference (OPD) and higher-order aberrations (HOA) were greater than mean total corneal aberrations values (p <0.001, p <0.001, respectively). 

It was concluded that the majority of HOAs at 6 mm were caused by epithelial remodeling (97.47%). The epithelial remodeling by thickening at the inner zone of the inlays and thinning at the area above the allogenic segment was a physiological response to correct the corneal front surface irregularity. Despite observed increases in epithelial aberration coefficients due to these changes, thickness variations in the epithelium were compensatory to corneal thickness, resulting in lower measured total corneal aberrations. Studies with larger series and different modalities are needed to better understand CAIRS biomechanics.