MAY 18, 2017
Cornea/External Disease, Refractive Mgmt/Intervention
Corneal collagen crosslinking (CXL) requires accurate measurement of the corneal stroma depth, both to avoid damage to adjacent tissue such as the endothelium and to assess treatment efficacy. The treatment depth may also be particularly important when subsequent photorefractive keratectomy (PRK) or LASIK is necessary. But because there is no gold standard for evaluating the post-CXL demarcation line in vivo, this prospective case series investigated the utility of 3 imaging modalities: confocal microscopy, OCT and Scheimpflug imaging.
Subjects included 20 eyes of 20 patients who underwent the standard CXL protocol. At 3 to 7 weeks postoperatively, the eyes were imaged with Scheimpflug tomography, OCT, and finally contact confocal microscopy. The authors examined two methods each of confocal microscopy and Scheimpflug imaging.
The CXL depths found by OCT and each confocal method correlated well with one another. Of these 3, the OCT measurements showed the lowest correlation and also low intraobserver reliability. Both of the Scheimpflug methodologies resulted in high variability and did not correlate with the other types.
Controversies or possible study limitations
Evaluation of the post-CXL demarcation line remains enigmatic as to date, there is no standardized method to confirm its existence, let alone its precise location. Additionally, the authors point out that their hypotonic riboflavin regimen could contribute to variation in the location of the demarcation line compared to prior findings. Finally, the baseline corneal thickness obtained from confocal microscopy is not accurate, making the final percentage calculations somewhat spurious.
The post-CXL demarcation line could be a clinically significant finding, helping clinicians evaluate the depth of CXL treatment. In turn, this depth would potentially help ascertain efficacy and endothelial safety of the procedure. The authors provide a beneficial study examining different clinical modalities for determining this demarcation line, and helping to establish which modalities have higher degrees of correlation.