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.
Ewa Maczynska, Alfonso Jimenez Villar, Jagoda Rzeszewska, Karol Karnowski, Maciej Wojtkowski, Bartlomiej Kaluzny, and Ireneusz Grulkowski, "IOP-related changes in corneal hysteresis derived from air-puff SS-OCT in ex vivo porcine eyes and in vivo human eyes (Conference Presentation)," Proc. SPIE 10496, Optical Elastography and Tissue Biomechanics V, 104960E (Presented at SPIE BiOS: January 27, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2290338.5751463324001.
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