Clinical Assessment of Micromechanical Alterations of the Cornea Post-Refractive Surgery Using Phase Decorrelation OCT

Abstract

Purpose : While clinical diagnosis and surgical planning remains rooted in morphology, a growing body of evidence demonstrates the essential role of localized corneal biomechanics in the development of ectatic disease. This work will report on an on-going clinical study determining the ability of temporal decorrelation OCT measurements to individually characterize normal corneas, distinguish keratoconus corneas, confirm crosslinking effect, and observe changes in the cornea post-refractive surgery.

Methods : Patients scheduled for either refractive surgery for corneal crosslinking were imaged pre-operatively and 3-6 months post operatively. Both M-B mode scans and B-mode scans were acquired along the vertical meridian, with a small offset nasally to avoid specular reflection. A simplified temporal correlation metric is calculated based on the complex-valued OCT signal in the time domain.

Results : Normal eyes exhibit expected relationships with respect to axial profile and repeatability and do not show dependence on central corneal thickness or refractive error (which confound some other methods of mechanical assessment.) There is a significant increase in the decorrelation metric in the keratoconus corneas as compared to normals (n=16, p=0.006), and in post-LASIK corneas as compared to pre-LASIK corneas (n=26, p<0.001). We interpret this increase in decorrelation to indicate that the cornea is less microstructurally constrained, which is consistent with the understanding of keratoconus as a focal weakening of the cornea. Further, we observe a decrease in decorrelation in post-CXL corneas (n=5, p<0.001), indicating a greater degree of microstructural constraint.

Conclusions : The ability of this OCT technique to identify microstructural changes could be a useful adjunct to refractive surgery screening criteria, or for earlier confirmation of a keratoconus diagnosis (as opposed to the current progression-based diagnosis) allowing patients to receive intervention earlier in the disease course.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Cornea cross-sectional images (A) backscatter intensity and (B) phase decorrelation OCT images. Images are 750μm axial x 4mm lateral.

 

Depth profiles of decorrelation coefficient in four different groups of corneas. Lower mobility coefficients indicate more microstructural constraint and higher tissue stability.