Abstract
Purpose :
The objective of the present study is to test the clinical potential of the Brillouin micro-spectroscopy technology in KC patients and to develop biomechanics-based diagnostic metrics, particularly for the detection of KC in early stages and for the evaluation of corneal stiffening following treatment with corneal collagen crosslinking (CXL).
Methods :
Studies were performed at Massachusetts General Hospital (MGH) and the Institute for Refractive and Ophthalmic Surgery (IROC) in Zurich, Switzerland, according to IRB-approved protocols. Recruited study subjects include 44 subjects with normal corneas (age 39.2+/-14.0 y/o), 62 subjects diagnosed with KC of varying severity (Stage I: n = 25, 36.1±11.7 y/o; Stage II: n = 9, 45±13.1 y/o; Stage III: n = 4, 47.3±12.3 y/o; Stage IV: n = 8, 45.6±15.9 y/o), and 37 KC patients treated with CXL in the past 4 years (age 34.6±10.8 y/o). Custom-built Brillouin optical microscopy systems using near infrared light were used to obtain Brillouin-shift maps of the corneas. Various biomechanical metrics based on the measured Brillouin shifts were analyzed.
Results :
In normal corneas, the Brillouin shifts were spatially uniform. By contrast, in both early and advanced stages of KC (I to IV) the Brillouin shifts at the thinnest point or cone regions were significantly (p < 0.001) lower than the values in the corneal periphery, indicating focal weakening. The regional difference correlates with the severity of KC and effectively cancels out the patient-to-patient variability in Brillouin shift, which makes average Brillouin shift an ineffective metric for the detection of early stage KC (I and II). CXL-treated corneas (n=16, 34.6 ± -10.8 y/o) showed higher Brillouin shifts (p < 0.05) compared to untreated, early-stage KC corneas (n = 8, 25.6 ± 10.7 y/o), in modest correlation with the elapsed time after CXL (= 0.16; n = 30, 29.7 ± 12.2 y/o, 24 males).
Conclusions :
The Brillouin biomechanics-based metrics revealed a clear difference between healthy and mild (stage I) KC corneas and between CXL-treated and non-treated KC corneas. These remarkable findings support the potential of Brillouin imaging for diagnosis and post-therapy monitoring of KC patients and warrants further clinical studies to test how these metrics enhance the early screening and management of KC patients.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.