Abstract
BackgroundThe corneal biomechanical properties with the prolongation of time after corneal refractive surgery are important for providing a mechanical basis for the occurrence of clinical phenomena such as iatrogenic keratectasia and refractive regression. The aim of this study was to explore the changes of corneal elastic modulus, and stress relaxation properties from the 6-month follow-up observations of rabbits after a removal of anterior corneal tissue in simulation to corneal refractive surgery.MethodsThe anterior corneal tissue, 6 mm in diameter and 30–50% of the original corneal thickness, the left eye of the rabbit was removed, and the right eye was kept as the control. The rabbits were normally raised and nursed for 6 months, during which corneal morphology data, and both of corneal hysteresis (CH) and corneal resistance factor (CRF) were gathered. Uniaxial tensile tests of corneal strips were performed at months 1, 3, and 6 from 7 animals, and corneal collagen fibrils were observed at months 1, 3, and 6 from 1 rabbit, respectively.ResultsCompared with the control group, there were statistical differences in the curvature radius at week 2 and month 3, and both CH and CRF at months 1, 2, and 6 in experiment group; there were statistical differences in elastic modulus at 1, 3, and month 6, and stress relaxation degree at month 3 in experiment group. The differences in corneal elastic modulus, stress relaxation degree and the total number of collagen fibrils between experiment and control groups varied gradually with time, and showed significant changes at the 3rd month after the treatment.ConclusionsCorneas after a removal of anterior corneal tissue undergo dynamic changes in corneal morphology and biomechanical properties. The first 3 months after treatment could be a critical period. The variation of corneal biomechanical properties is worth considering in predicting corneal deformation after a removal of anterior corneal tissue.
Highlights
The corneal biomechanical properties with the prolongation of time after corneal refractive surgery are important for providing a mechanical basis for the occurrence of clinical phenomena such as iatrogenic keratectasia and refractive regression
The clinical follow-up results within one year after operation showed that the related parameters of corneal biomechanics will change [7,8,9], and the corneal biomechanical parameters fluctuate with time, such as corneal hysteresis (CH) and corneal resistance factor (CRF) output by Ocular Response Analyzer (ORA) [10,11,12,13]
Because the corneal anterior surface changes largely compared to posterior surface immediately after treatment, and the change of posterior surface is an important index for the diagnosis of corneal ectasia [31, 32] postoperatively, only the curvature radius of posterior surface were calculated based on Optical coherence tomography (OCT) images according the method shown in our previous study [33]
Summary
The corneal biomechanical properties with the prolongation of time after corneal refractive surgery are important for providing a mechanical basis for the occurrence of clinical phenomena such as iatrogenic keratectasia and refractive regression. The clinical follow-up results within one year after operation showed that the related parameters of corneal biomechanics will change [7,8,9], and the corneal biomechanical parameters fluctuate with time, such as corneal hysteresis (CH) and corneal resistance factor (CRF) output by Ocular Response Analyzer (ORA) [10,11,12,13]. The clinical observation results of dynamic corneal response parameters output by Corneal Visualization Scheimpflug Technology (Corvis ST) showed that stiffness parameter at applanation A1 (SPA1) decreased during 6 months after corneal refractive surgery [9, 14]. The above clinical retrospective studies showed that the changes of ORA and Corvis ST output parameters with time after corneal refractive surgery. Most of the dynamic corneal response parameters are affected by central corneal thickness (CCT) [15, 16] and intraocular pressure (IOP) [17], there may be misunderstandings about the interpretation of the results after refractive surgery
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