We demonstrate micro-scale vibrations of the porcine corneas as the result of the stimulation of the eye with air puff. Phase-resolved swept-source optical coherence tomography instrument was used to examine the post-air-puff reaction of the corneas. The impact of the intraocular pressure on vibration amplitude and frequency was examined. The results showed characteristic modes of vibration that will be correlated with the intraocular pressure level. The presented approach represents the next step towards understanding the eye dynamics due to air-puff-based mechanical stimulation.
KEYWORDS: In vivo imaging, Cornea, Elastography, Optical coherence tomography, Coherence (optics), Tissues, Control systems, Modulation, Eye, Animal model studies
Biomechanical properties of the cornea play key role in accurate measurement of the intraocular pressure (IOP). The aim of this study is to assess the impact of IOP on corneal hysteresis in porcine (ex vivo) and human (in vivo) eyes using swept source optical coherence tomography combined with the air-puff system (air-puff SS-OCT).
We developed air-puff SS-OCT to assess rapid dynamics of porcine corneas during the air pulse application. Both tissue displacement x(t) and air stimulus F(t) are acquired simultaneously that enables generation of corneal hysteresis F(x), which is a direct signature of viscoelastic properties of the cornea. The hysteresis loop can be quantified by calculation the parameters including maximum apex displacement, central corneal thickness, hysteresis area, elastic moduli etc.
Firstly, the corneal response of 35 ex-vivo porcine eyes to the air puff is determined for IOP ranging from 5 to 35 mmHg. The IOP level is set by a custom pressure control system. The IOP causes highly correlated changes in the proposed parameters of the hysteresis curve. Secondly, we investigate the modification of corneal hysteresis in 30 human corneas in vivo. The IOP is modulated by installation of 0,2% brimonidine eye drops (Alphagan) decreasing the IOP. The IOP is measured with air-puff non-contact tonometer (Topcon) and Goldmann tonometer and compared with hystereses generated by air-puff SS-OCT.
To conclude, IOP generates changes of corneal viscoelasticity in ex vivo animal model and in vivo human eyes. Non-invasive character, micrometer resolution and fast acquisition make our approach attractive for in vivo studies.
In this paper, we use swept source optical coherence tomography combined with air-puff module (air-puff SS-OCT) to
investigate the properties of the cornea. During OCT measurement the cornea was stimulated by short, air pulse, and
corneal response was recorded. In this preliminary study, the air-puff SS-OCT instrument was applied to measure behavior
of the porcine corneas under varied, well-controlled intraocular pressure conditions. Additionally, the biomechanical
response of the corneal tissue before, during and after crosslinking procedure (CXL) was assessed. Air-puff swept source
OCT is a promising tool to extract information about corneal behavior as well as to monitor and assess the effect of CXL.
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