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Gianfranco Bianco, Luigi Bruno, Massimo Antonio Fazio; Characterization Method for the IOP-time-dependent Cornea and Sclera Biomechanics. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3152.
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© ARVO (1962-2015); The Authors (2016-present)
To present an optical characterization method for measuring time-dependent corneo-sclera shell biomechanics, through an integration of Electronic Laser Speckle Interferometry (ESPI) and 3D geometry reconstruction.
The posterior pole of a human donor eye has been inflation tested to record the time-varying displacement and strain fields in the peripapillary and mid-peripheral sclera. The pressure inside the eye was abruptly elevated by manually switching pressure between two PBS reservoirs set at 5 and 30 mmHg (IOP-transient test). The anterior pole from the same donor eye was later inflation tested by steadily increasing the IOP for the same pressure range. A custom-built ESPI composed of a laser and four synchronized cameras simultaneously recorded the time-varying deformations with nanometric accuracy (<30 nm) and an imaging rate of 180Hz. The multi-camera optical set-up allowed for a 3D stereo geometry reconstruction of the specimen shapes with an accuracy lower than 25 μm.
The IOP elevation in the cornea generated high values of strain in the limbus region, close to the apex, and around muscle insertions (Fig. 1, right). In the sclera, high gradients of strain were observed around the optic nerve but not in the mid-peripheral region (Fig.1, left). In the IOP-transient test the peripapillary and mid-peripheral sclera showed a similar overall average deformation rate during the IOP rapid increase (1000<time<2500 µs), while once relaxation was reached (time>3000 µs) the peripapillary sclera showed higher displacements than the mid-peripheral.
Thanks to the high rate interferometric imaging, the dynamic response of the corneo-sclera shell can be finely resolved in both the spatial and temporal domain. This will allow for the investigation of the corneo-sclera mechanical response to time-varying IOP, and how its biomechanics is altered in ocular diseases like glaucoma, myopia, and keratoconus.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Strain field mapped on the textured 3D model: sclera (left) and cornea (right). The custom ESPI merges displacements and specimen geometry data to finely resolve the local spatial distribution of the IOP-time-dependent deformations.
Average of the time-dependent displacement magnitude in the peripapillary and mid-peripheral regions for a rapid IOP increase (ΔIOP= 5-30 mmHg). The two regions deformed similarly during the transitory, but notabley different once the IOP stabilized (time>3000 μs).
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