Measurement of In Vivo Biomechanical Changes Attributable to Epithelial Removal in Keratoconus Using a Noncontact Tonometer

Abstract

Purpose: To compare the biomechanical properties of the cornea after epithelial removal in eyes with keratoconus undergoing corneal cross-linking. Methods: Prospective interventional case series at a university hospital tertiary referral center. Corneal biomechanical properties were measured in patients with keratoconus undergoing corneal cross-linking, immediately before and after epithelial debridement by using a dynamic ultrahigh-speed Scheimpflug camera equipped with a noncontact tonometer. Results: The study comprised 45 eyes of 45 patients with a mean age of 19.6 ± 4.9 years (range 14–34). The cornea was found to be 23.7 ± 15.7 μm thinner after epithelial removal (P < 0.01). Corneal stiffness was reduced after epithelial removal as demonstrated by a significant decrease of parameters such as stiffness parameter A1 (12.31, P < 0.01), stiffness parameter-highest concavity (2.25, P < 0.01), A1 length (0.13 mm, P = 0.04), highest concavity radius of curvature (0.26 mm, P = 0.01), highest concavity time (0.22 ms, P = 0.04) and an increase in A1 velocity (−0.01 m/s, P = 0.01), A1 deformation amplitude (−0.03 mm, P ≤ 0.01), A1 deflection length (−0.32 mm, P < 0.01), A2 deformation amplitude (−0.03 mm, P = 0.01), and A2 deflection length (−1.00 mm, P < 0.01). There were no significant differences in biomechanical intraocular pressure (0.15 mm Hg, P = 0.78), deformation amplitude (0.03, P = 0.54), maximum inverse radius (−0.01 mm, P = 0.57), and whole eye movement length (−0.02 mm, P = 0.12). Conclusions: Dynamic ultrahigh-speed Scheimpflug camera equipped with a noncontact tonometer offers an alternative method for in vivo measurements of the epithelial layer's contribution to corneal biomechanical properties. Our results suggest that corneal epithelium may play a more significant role in corneal biomechanical properties in patients with keratoconus than previously described.

Relationship between corneal biomechanical parameters and corneal sublayer thickness measured by Corvis ST and UHR-OCT in keratoconus and normal eyes

“…Our results also supports this hypothesis. Ziaei et al compared the biomechanical parameters of the cornea after epithelial removal in eyes with KC undergoing corneal cross-linking and suggested that corneal epithelium may play a more significant role in corneal biomechanical properties in patients with KC, which was in line with our results [17]. Previous studies have demonstrated that the corneal stroma mainly consists of collagen lamellae and accounts for nearly 90% of the total thickness of the cornea [20].…”

“…Zhao et al reported the significant relationship between corneal stiffness and thinnest corneal thickness in KC [16]. Ziaei et al demonstrated that corneal epithelial removal in eyes with KC undergoing cross-linking seemed to alter corneal biomechanical integrity and make the cornea more prone to deformation [17]. Seiler et al found that Bowman's layer does not contribute significantly to biomechanical stability within the normal cornea [18].…”

Repeatability of corneal and epithelial thickness measurements with anterior segment optical coherence tomography in keratoconus

“…helpful when contemplating combined treatments with CXL and therapeutic laser ablations in patients with ectasia, as they often have an irregular corneal epithelial thickness profile [3,22]. CT and ET measurements have previously been shown to be highly repeatable in normal eyes using various OCT devices [23][24][25].…”

Corneal Biomechanical Properties in Varying Severities of Myopia

“…In recent years a wide variety of work has been completed on corneal biomechanics in health and disease with the introduction of non-invasive devices able to measure in vivo biomechanical parameters (Perez-Rico et al, 2015;Lee et al, 2016b;Vinciguerra et al, 2016). A better understanding of corneal biomechanical response can allow for better diagnosis and staging of various corneal disorders, refinement of suitable patients for refractive surgery or intrastromal ring segment implantation and provide further insights into biomechanics-modulating treatments such as corneal crosslinking (CXL) and keratoplasty (Kling and Hafezi, 2017;Ziaei et al, 2019Ziaei et al, , 2020. However, the analysis and evaluation of corneal biomechanics is complex as the cornea is a viscoelastic tissue.…”