Changes in posterior corneal elevations after combined transepithelial photorefractive keratectomy and accelerated corneal collagen cross-linking: retrospective, comparative observational case series.

Hun Lee,David Sung Yong Kang,Jin Young Choi,Byoung Jin Ha,Tae-Im Kim,Kyoung Yul Seo,Eung Kweon Kim

doi:10.1186/s12886-016-0320-3

Abstract

BackgroundTo compare the changes in anterior and posterior corneal elevations after combined transepithelial photorefractive keratectomy (PRK) and accelerated corneal collagen cross-linking (CXL) and after PRK.MethodsMedical records of 82 eyes of 44 patients undergoing either combined transepithelial PRK and CXL (PRK-CXL group) or transepithelial PRK (PRK group) were examined retrospectively. Changes in anterior and posterior corneal elevations were calculated by fitting an 8.0-mm diameter best-fit sphere and best-fit toric ellipsoid (BFTE) to the corneal shape with a fixed eccentricity of 0.4 using Scheimpflug tomography (Pentacam HR; Oculus Optikgeräte GmbH, Wetzlar, Germany) preoperatively and 6 months postoperatively.ResultsIn anterior corneal elevation, both groups demonstrated a similar trend of a forward displacement of peripheral anterior corneal surface and a backward displacement of central anterior corneal surface. In posterior corneal elevation, a forward displacement of peripheral posterior corneal surface was induced in both groups, along with a backward displacement of central posterior corneal surface, regardless of the calculation method. The magnitudes of displacement of peripheral and central posterior corneal surfaces were significantly smaller in the PRK-CXL group than in the PRK group. Moreover, the PRK-CXL group showed a backward displacement of posterior corneal surface at maximum corneal elevations when the BFTE was used as the reference surface.ConclusionsTransepithelial PRK combined with prophylactic CXL significantly reduced the magnitudes of displacement of peripheral and central posterior corneal surfaces, with the radius of the BFTE was set to 8.0-mm on the Scheimpflug tomography system.

Highlights

To compare the changes in anterior and posterior corneal elevations after combined transepithelial photorefractive keratectomy (PRK) and accelerated corneal collagen cross-linking (CXL) and after PRK
Elevation of the posterior corneal surface can occur after myopic photorefractive keratectomy (PRK) and laser in-situ keratomileusis (LASIK) [1,2,3]
The analysis revealed that there was no significant difference between the PRK-CXL and PRK groups in age, spherical or cylindrical refractive error, spherical equivalent refraction, keratometric values, optical zone, total ablation zone, or ablation depth, except for central corneal thickness (CCT) (Table 1)

Summary

Introduction

To compare the changes in anterior and posterior corneal elevations after combined transepithelial photorefractive keratectomy (PRK) and accelerated corneal collagen cross-linking (CXL) and after PRK. Collagen cross-linking (CXL) is a recently developed surgical procedure whereby riboflavin sensitization with ultraviolet-A (UVA) radiation induces stromal crosslinking [11] This procedure alters corneal biomechanics and increases mechanical rigidity (i.e., strengthens the corneal tissue) in porcine and human corneas, resulting in significant increases in the stiffness of the anterior corneal stroma [12]. A recently introduced accelerated CXL protocol consisting of higher-intensity light applied for a shorter period of time can be applied in various clinical settings [15] The outcomes of this protocol are comparable to those of conventional CXL, with no evidence of endothelial cell density changes [16]

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