Comparison of four methods of surface roughness assessment of corneal stromal bed after lamellar cutting.

Clotilde Jumelle,Virginie Dumas,Alina Hamri,Gilles Thuret,Sandrine Pereira,Gregory Egaud,Stephanie Reynaud,Cyril Mauclair,Philippe Gain,Thibaud Garcin

doi:10.1364/boe.8.004974

Abstract

Corneal lamellar cutting with a blade or femtosecond laser (FSL) is commonly used during refractive surgery and corneal grafts. Surface roughness of the cutting plane influences postoperative visual acuity but is difficult to assess reliably. For the first time, we compared chromatic confocal microscopy (CCM) with scanning electron microscopy, atomic force microscopy (AFM) and focus-variation microscopy (FVM) to characterize surfaces of variable roughness after FSL cutting. The small area allowed by AFM hinders conclusive roughness analysis, especially with irregular cuts. FVM does not always differentiate between smooth and rough surfaces. Finally, CCM allows analysis of large surfaces and differentiates between surface states.

Highlights

The cornea is the transparent lens-shaped tissue that forms the anterior part of the eye and provides two-thirds of its refractive power
3.1 Effect of dehydration and metallization on surface appearance by scanning electron microscopy Surface appearance was generally similar with eSEM and standard SEM (sSEM) (Fig. 3), but image contrast was lower with eSEM than with sSEM
3.2 Effect of dehydration and metallization on roughness measurement by chromatic confocal microscopy For the three lamellae cut by femtosecond laser (FSL), surface roughness measured by CCM did not differ between measurements performed on hydrated lamellae and after dehydration and metallization, with an RMS of 330, 365 and 412 before treatment and of 359, 385, 397 after treatment

Summary

Introduction

The cornea is the transparent lens-shaped tissue that forms the anterior part of the eye and provides two-thirds of its refractive power. It consists of approximately 300 collagen lamellae, arranged and interwoven in multiple directions for stiffness and optical properties. Some show a relatively similar roughness of corneal cuts for MKT and FSL [8, 9], while others favor MKT [10, 11] or FSL [12, 13] This is due to at least three factors: 1/ the authors’ use of various devices and cutting parameters, which are continually being improved; 2/ the variability of the response of corneal tissue, of which the collagen structure organization and stiffness vary with depth and maybe with age. The superficial flaps created by LASIK (80-120 um under the corneal surface) are cut from collagen stiffer than that in the posterior cornea, which is cut for certain corneal grafts (500 um under the surface); 3/ the lack of standardization between roughness-assessment techniques

Methods

Results

Conclusion