Corneal Viscoelastic Properties from Finite-Element Analysis of In Vivo Air-Puff Deformation

Abstract

Biomechanical properties are an excellent health marker of biological tissues, however they are challenging to be measured in-vivo. Non-invasive approaches to assess tissue biomechanics have been suggested, but there is a clear need for more accurate techniques for diagnosis, surgical guidance and treatment evaluation. Recently air-puff systems have been developed to study the dynamic tissue response, nevertheless the experimental geometrical observations lack from an analysis that addresses specifically the inherent dynamic properties. In this study a viscoelastic finite element model was built that predicts the experimental corneal deformation response to an air-puff for different conditions. A sensitivity analysis reveals significant contributions to corneal deformation of intraocular pressure and corneal thickness, besides corneal biomechanical properties. The results show the capability of dynamic imaging to reveal inherent biomechanical properties in vivo. Estimates of corneal biomechanical parameters will contribute to the basic understanding of corneal structure, shape and integrity and increase the predictability of corneal surgery.

Observation of sound-induced corneal vibrational modes by optical coherence tomography

“…Corneal hysteresis has shown to be reduced in ectatic disease, but its sensitivity and specificity have been insufficient to differentiate normal eyes from low-grade keratoconus [6]. Air-puff can be combined with Scheimpflug camera [7] or optical coherence tomography (OCT) [8] for image-based analysis and estimates of corneal viscoelastic parameters [9]. Other emerging techniques for measuring elastic modulus with spatial resolution include supersonic shear imaging [10], optical coherence elastography [11][12][13][14][15][16], and Brillouin microscopy [17].…”

Biomechanical Differences Between Femtosecond Lenticule Extraction (FLEx) and Small Incision Lenticule Extraction (SmILE) Tested by 2D-Extensometry in Ex Vivo Porcine Eyes

“…In this case no mechanical difference can be expected. Also, in vivo measurements of corneal biomechanics after SmILE and LASIK surgery using air-puff deformation systems are inconclusive [11][12][13]17,33 potentially because they do not measure long-term deformation, which is essential for maintaining the corneal shape over time. In our experimental setting we applied the load gradually from the posterior surface and then measured its relaxation behavior under constant load.…”

“…Only few experimental studies have analyzed differences in the in vivo corneal deformation response following an air puff, 10-12 but they did not find a significant difference between FLEx and SmILE procedures. It should be noted that the corneal deformation response following an air puff is very sensitive to changes in corneal thickness, 13 which might have masked the subtle differences between FLEx and SmILE in this setup. In addition, the strain during air-puff deformation is induced very rapidly; this makes it impossible to retrieve long-term viscoelastic properties, which are particularly important for the stability after refractive surgery.…”

Applanation optical coherence elastography: noncontact measurement of intraocular pressure, corneal biomechanical properties, and corneal geometry with a single instrument

“…1 In addition to IOP measurements, applanation studies have been performed in hope to quantify corneal biomechanical properties for detecting degenerative diseases such as keratoconus. 2 However, the large displacements induced by the air-puff prohibit local assessment of corneal biomechanical properties 3 and cause nonlinear biomechanical behaviors. 4 Moreover, biomechanical measurements of the cornea are confounded by other parameters, such as IOP 5,6 and central corneal thickness (CCT).…”

“…2 However, assumptions of corneal linear mechanical responses are not applicable here as the corneal deformation is large (mm-scale), and the corneal stress-strain curve is distinctly nonlinear. 28 There are some limitations in our work as well.…”