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Judith Birkenfeld, Antoine Ramier, Behrouz Tavakol, Susana Marcos, Seok-Hyun (Andy) Yun; Assessment of ocular mechanical resonances using phase-sensitive OCT and frequency-domain air puff stimulation. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1407.
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© ARVO (1962-2015); The Authors (2016-present)
Mechanical resonances are an intrinsic property of a system, and are a promising way of measuring its mechanical properties. The observation of vibrational modes in the cornea is a potential technique to measure corneal stiffness which plays an important role in corneal pathology. Here, we evaluate the capability of an integrated focused air-puff system to excite mechanical resonances of ex vivo porcine corneas.
A custom-build air puff system applied a frequency train of micron-level air-puffs onto the cornea. The duration of the puffs was 1-2 ms, and the puff frequencies were linearly swept between 20-500 Hz in steps of 1, 10, or 20 Hz. The airpuff was coupled to a phase-sensitive swept source OCT system, and M-mode OCT imaging and vibrometry was performed at a specific location on the cornea. The frequency-dependence of the amplitude and phase of corneal vibration allowed to identify the fundamental vibration mode of the sample. The optical beam of the OCT system was then scanned over an area of 5x5 mm to 10x10 mm at the identified resonance frequency. The technique was tested on 4 freshly enucleated porcine eyes (whole eye globe) at constant IOP. Measurements were obtained at different IOP (17 & 11 mmHg), different pressure levels of the air-puff (100-250 kPa at air source), at the corneal apex or at the periphery, and for different nozzle angles (±10°), and nozzle/sample distances (±5 mm).
The fundamental vibration mode was consistently observed across different samples at a mean frequency of 273 ± 33 Hz. The amplitude of corneal displacement scaled linearly with increasing puff pressure and was on the order of 1 μm/50 kPa. The resonance frequencies were independent from puff pressure. A decrease in intraocular pressure was found to induce a decrease in resonance frequency and a higher vibration amplitude, a result that is consistent with earlier findings. Within applied range, the results were not dependent on corneal location and variations in air-puff setup.
The use of a focused air-puff as a puff train allows frequency domain analysis of the ocular mechanical resonance.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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