Assessment of the Association Between In Vivo Corneal Biomechanical Changes After Corneal Cross-linking and Depth of Demarcation Line

Abstract

PURPOSE: To test for an association between stiffening following corneal cross-linking (CXL) and demarcation line depth. METHODS: Sixty-six eyes of 66 patients treated with CXL for progressive keratoconus were included. Dynamic corneal response parameters (DCRs) were measured with the Corvis ST (Oculus Optikgeräte GmbH; Wetzlar, Germany) on the day of CXL and after 1 month. Demarcation line was measured 4 weeks after CXL. A multivariate general linear model was used to test for an association between the change in DCRs and the ratio between demarcation line depth and the postoperative pachymetry. RESULTS: The authors found no significant associations between the change in inverse concave integrated radius (1/R) and the demarcation line ratio ( P = .46), age ( P = .33), sex ( P = .11), preoperative maximum keratometry ( P = .10), and laterality ( P = .82). Similarly, there was no significant correlation between the change in 1/R and the demarcation line ratio ( R 2 = .002 and P = .75). However, there was a significant association between the preoperative values of 1/R and the respective change in 1/R ( P < .0001). The change in 1/R was inversely proportional to the patient's preoperative 1/R; stiffer corneas (lower values of 1/R) were less affected than less stiff corneas ( R 2 = .23, P < .0001). CONCLUSIONS: CXL is associated with changes in DCRs, suggesting a change in corneal biomechanics following CXL. These changes do not appear to be associated with the demarcation line depth. [ J Refract Surg . 2019;35(3):202–206.]

Comparison of waveform-derived corneal stiffness and stress-strain extensometry-derived corneal stiffness using different cross-linking irradiances: an experimental study with air-puff applanation of ex vivo porcine eyes

“…This was also shown in vivo for standard [27] and accelerated protocols [26,47,48]. Additionally, in recent studies, the deformation amplitude ratio (DA ratio) was decreased after CXL in different cohorts, whereby not all data showed significance [26,27,47,48]. These results are in line with the definition, which states that higher values of the DA ratio are associated with softer corneas [22].…”

“…Post-treatment significantly decreased in our results for all protocols. This was also shown in vivo for standard [27] and accelerated protocols [26,47,48]. Additionally, in recent studies, the deformation amplitude ratio (DA ratio) was decreased after CXL in different cohorts, whereby not all data showed significance [26,27,47,48].…”

“…SP A1 is the stiffness parameter calculated for reaching the first applanation (A1), which was significantly increased in standard and accelerated protocols. In literature, there are some in vivo reports that have shown increased values as well but not all were significant [ 26 , 27 , 47 , 48 ]. Corneal stiffness expressed in newtons per meter (Kc[mean], Kc[linear]) showed a similar increase in S-CXL and A-CXL (9*10), whereas A-CXL (18*5) was less pronounced compared to SP A1.…”

The Role of Corneal Biomechanics for the Evaluation of Ectasia Patients

“…Understanding the material and structural properties of the cornea has gained increased clinical utility over the latest decades. Knowledge of fundamental biomechanical principles has been applied in several clinical conditions [1,2], including correcting intraocular pressure measurements [3,4], planning and following corneal collagen crosslinking treatments [5][6][7][8], and elective keratorefractive surgery [9,10]. Specifically, in the field of refractive surgery, the investigation of corneal biomechanical properties turned out to be a very relevant part of the screening process, in an attempt to identify patients at higher risk (susceptible) to develop iatrogenic ectasia after laser vision correction (LVC) [9][10][11].…”

Experimental Assessment of the Spatial and Temporal Distribu-Tion of Non-contact Tonometer Airflows

“…Through the use of this data and empirically derived algorithms, the device is able to offer measures of corneal hysteresis and corneal resistance factors that can be considered with the intraocular pressure measurements. [2] Despite significant efforts to understand corneal biomechanics with the use of the CorvisST and ORA [6][7][8][9][10][11][12][13][14][15][16], there is a dearth of literature on the actual physical and geometric properties of the airflow pressure applied to the cornea with these devices. Indeed, the physical attributes of the air-pressure applied during non-contact tonometry is fundamental to the measures of both intraocular pressure and corneal biomechanics.…”