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Brecken Blackburn, Shi Gu, Matthew R Ford, Vinicius Silbiger De Stefano, Michael Jenkins, William J Dupps, Andrew Rollins; Phase-Decorrelation OCT for Noncontact Measurement of Biomechanical Effects of Corneal Crosslinking. Invest. Ophthalmol. Vis. Sci. 2018;59(9):745.
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© ARVO (1962-2015); The Authors (2016-present)
With mounting evidence that common corneal ectasias are causally linked to biomechanical abnormalities, there is a clear need for noninvasive methods of measuring corneal biomechanical properties. Existing methods of biomechanical assesment have various drawbacks: dependence on intraocular pressure (IOP), long acquisition time, limited resolution, and expensive equipment. Here, we present a method which may avoid these limitations by using existing optical coherence tomography systems to detect the endogenous random motility within the cornea which can be associated with degree of stromal crosslinking.
The principle of phase-decorrelation optical coherence tomography (PhD-OCT) is based on dynamic light scattering measurement of Brownian motion. The direct result of these measurements is a decorrelation coefficient, which yields an “apparent diffusion coefficient”, D. In the cornea, D represents the degree of confinement of collagen within the stroma. A series of ex vivo corneal crosslinking (CXL) experiments was conducted by applying the Dresden protocol to porcine whole globes. Further benchtop experiments determined the effects of external factors, such as IOP, on PhD-OCT. In addition, human patients were imaged with PhD-OCT using a clinical OCT system.
In both the ex vivo porcine cornea and the in vivo human cornea, crosslinking results in the anterior third of the corneal stroma becoming more confined, indicating more crosslinks. This effect was highly repeatable in ex vivo porcine corneas (change in average D = -41.55±9.64%, n=5) and not seen after sham treatments (change in average D = 2.83±12.56%, n=5). (Fig 1) In patients, a similar effect was observed in post-CXL corneas and not observed in untreated corneas. (Fig 2) No dependence of PhD-OCT on IOP was found, while correctable effects were found to be caused by variations of SNR, hydration, incidence angle, as well as axial and lateral motion.
PhD-OCT may be a useful and readily translatable tool for investigating biomechanical properties of the cornea and for enhancing the diagnosis and treatment of patients.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Demonstration of apparent diffusion coefficient (µm2/s) decrease after CXL in ex vivo porcine eyes. Images 5mm lateral, 2mm axial. (D) Mean D of anterior third.
Demonstration of apparent diffusion coefficient (µm2/s) decrease in patients with and without CXL treatment. Images 7mm lateral, 2mm axial.
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