The Impact of Epithelial Remodeling on Surgical Techniques Used in Topography-guided Surface Ablation in Irregular Corneas

Abstract

PURPOSE: To analyze the optical consequences of epithelial remodeling in irregular corneas and their impact on the choice of different surface ablation techniques. METHODS: Anterior corneal and stromal surface topographies and epithelial thickness maps were analyzed in 24 eyes with irregular corneal optics. On two of the eyes, four different surface ablation techniques were simulated: (1) conventional anterior topography-guided photorefractive keratectomy (PRK), (2) transepithelial phototherapeutic keratectomy (PTK), (3) transepithelial anterior topography-guided PRK, and (4) stromal topography-guided PRK. RESULTS: Stromal surface topographies showed higher keratometric values, astigmatism, asphericity, and corneal higher order aberrations compared to topographies of anterior corneas covered by epithelium. Transepithelial anterior topography-guided PRK and stromal topography-guided PRK both resulted in regularized stromal surface, transepithelial PTK achieved partial regularization corresponding to the smoothing effect of the epithelial remodeling, and conventional anterior topography-guided PRK delivered after epithelial removal resulted in residual stromal surface irregularities. CONCLUSIONS: The difference in optical landscapes between the stromal and anterior surfaces in irregular corneas will represent a source of error when anterior topography-guided treatments are delivered on the deepithelialized stroma, as in conventional PRK. In contrast, anterior topography-guided ablations performed as transepithelial PRK and stromal topography-guided PRK delivered after epithelial removal address the full stromal irregularity, whereas transepithelial PTK alone may be used when topography-guided treatments are not possible. The authors conclude topography-guided PRK of irregular corneas should lead to significantly improved regularization only if it includes the effect of epithelial remodeling. [ J Refract Surg . 2022;38(8):529–537.]

Asymmetric Intrastromal Corneal Ring Segments with Progressive Base Width and Thickness for Keratoconus: Evaluation of Efficacy and Analysis of Epithelial Remodeling

“…These variations in the distribution of epithelial thickening can be accounted for by the compensatory function of epithelial remodeling, which reduces the underlying irregular redistribution of the stroma by increasing or decreasing the thickness of epithelial cell layers to “compensate” for variations along the length of the ICRS [ 38 ]. Epithelial thinning can decrease corneal curvature and HOAs [ 39 ]. We suggest that the asymmetric epithelial profile induced by the ICRS may help to decrease coma aberration after asymmetric ICRS implantation.…”

Ray-Tracing Transepithelial Excimer Laser Central Corneal Remodeling Plus Pachymetry-Guided Accelerated Corneal Crosslinking for Keratoconus

“…The system also registers and treats the epithelium and stroma separately. 7 Regarding CXL, 19 the same protocol was not used for all patients. The pachymetry-guided protocol 24 enables us to customize the ACXL strategy in many ways by setting the depth of the DL according to residual postablation stromal pachymetry, thus sparing the endothelium, using accelerated protocols to shorten UV-A illumination time and the pulsed light mode of exposure.…”

“…To obtain high-resolution maps required for customized corneal surgery, the Precisio 2 system exploits an ultrathin blue laser slit, analyzing the scattered light of all corneal layers, to measure epithelial thickness independently from the lacrimal film because scattering is absent in liquids; a 6D eye-tracker, built in to compensate the eye movements during the acquisition; and a voice-driven examination autoacquisition to negate possible subjective errors induced by the operator. 7…”

“…[1][2][3][4] The combined Ray-Tracing-Guided (RT t-PRK) plus ACXL consists of a minimally invasive ray-tracing-based customized transepithelial excimer laser central corneal remodeling (CCR) to improve the whole natural and spectacle-corrected quality of vision (QoV), reducing the high-order aberrations (HOAs) while consuming a small amount of corneal stroma. [5][6][7] The use of combined topography-guided t-PRK plus crosslinking (CXL) represents a therapeutic reality performed in selected cases in many countries over the past decade. 8 The long-term follow-up studies have demonstrated the efficacy and safety of these procedures in improving the UCVA and BSCVA of patients with KC performed simultaneously (on a same-day basis) or sequentially (6 months at least after CXL).…”

“…1–4 The combined Ray-Tracing-Guided (RT t-PRK) plus ACXL consists of a minimally invasive ray-tracing–based customized transepithelial excimer laser central corneal remodeling (CCR) to improve the whole natural and spectacle-corrected quality of vision (QoV), reducing the high-order aberrations (HOAs) while consuming a small amount of corneal stroma. 5–7…”