3D Assessment of Corneal Crosslinking with Phase-Decorrelation OCT

Abstract

Purpose : While corneal crosslinking (CXL) is becoming standard practice, there are few tools with which to directly measure its effectiveness in modulating biomechanical properties of the cornea. Because it is hypothesized that the biomechanical changes induced by CXL are the key to the beneficial effects of the treatment, tools to measure corneal biomechanics with high resolution are needed in evaluate different CXL protocols. In this study, we show that phase-decorrelation optical coherence tomography (PhD-OCT) may resolve corneal crosslinking both in depth and transversely, as demonstrated in accelerated and patterned CXL.

Methods : PhD-OCT uses a conventional spectral domain OCT system (1300nm, 47kHz) to gather M-B scans of a sample, then analyzes each M-scan for axially resolved, short time-scale temporal decorrelation. This technique has previously been shown to be sensitive to the degree of corneal crosslinking. In this work, two experiments were conducted on intraocular pressure-controlled ex vivo porcine corneas. First, four corneas were treated so that each third of the cornea was treated with either the traditional Dresden protocol (UV: 3mW/cm² for 30 min), or one of two accelerated CXL protocols (UV: 9mW/cm² for 9 minutes or 30mW/cm² for 3 minutes). Second, four corneas were covered with a patterned mask and then treated with the Dresden protocol.

Results : Significant differences were observed in the depth of crosslinking between the three CXL protocols with the longer duration methods having deeper crosslink penetration. (Example in Fig 1) The difference between crosslinked and non-crosslinked regions due to the patterned mask was evident, (within one sample, masked Γ: 1.9e-4±4.8e-5, unmasked Γ: 1.60e-4 ±4.37e-5, p<0.05). (Fig 2)

Conclusions : These results agree with existing literature on the relationship between acceleration of CXL and crosslink penetration depth. Further, the results support the idea that PhD-OCT without hardware modifications to existing OCT systems could image the axial and lateral extent of CXL. This may be useful for optimizing CXL protocols or customizing treatments.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Plot showing the decorrelation parameter Γ as a function of depth from anterior surface with two accelerated CXL protocols compared to standard protocol. These data are from one eye which was given treatments in three distinct regions.

 

En face PhD images of an ex vivo cornea undergoing a patterned CXL.