title: Biomechanical characterization of keratoconus corneas ex vivo with Brillouin microscopy.
abstract: OBJECTIVE
  Loss of corneal strength is a central feature of keratoconus progression. However, it is currently difficult to measure corneal mechanical changes noninvasively. The objective of this study is to evaluate if Brillouin optical microscopy can differentiate the mechanical properties of keratoconic corneas versus healthy corneas ex vivo.
  
  
  METHODS
  We obtained eight tissue samples from healthy donor corneas used in Descemet's stripping endothelial keratoplasty (DSEK) and 10 advanced keratoconic corneas from patients undergoing deep anterior lamellar keratoplasty (DALK). Within 2 hours after surgery, a confocal Brillouin microscope using a monochromatic laser at 532 nm was used to map the Brillouin frequency shifts of the corneas.
  
  
  RESULTS
  The mean Brillouin shift in the anterior 200 μm of the keratoconic corneas at the cone was measured to be 7.99 ± 0.10 GHz, significantly lower than 8.17 ± 0.06 GHz of the healthy corneas (P < 0.001). The Brillouin shift in the keratoconic corneas decreased with depth from the anterior toward posterior regions with a steeper slope than in the healthy corneas (P < 0.001). Within keratoconic corneas, the Brillouin shift in regions away from the apex of the cone was significantly higher than within the cone region (P < 0.001).
  
  
  CONCLUSIONS
  Brillouin measurements revealed notable differences between healthy and keratoconic corneas. Importantly, Brillouin imaging showed that the mechanical loss is primarily concentrated within the area of the keratoconic cone. Outside the cone, the Brillouin shift was comparable with that of healthy corneas. The results demonstrate the potential of Brillouin microscopy for diagnosis and treatment monitoring of keratoconus.
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Cambridge, Massachusetts, United States Department of Dermatology, Harvard Medical School, Boston, Massachusetts, United States.
authors.forename: Giuliano
authors.initials: G
authors.lastname: Scarcelli
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Cambridge, Massachusetts, United States Department of Dermatology, Harvard Medical School, Boston, Massachusetts, United States.
authors.forename: Sebastien
authors.initials: S
authors.lastname: Besner
authors.affiliation: Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, United States.
authors.forename: Roberto
authors.initials: R
authors.lastname: Pineda
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Cambridge, Massachusetts, United States Department of Dermatology, Harvard Medical School, Boston, Massachusetts, United States Harvard-MIT Health Sciences and Technology, Cambridge, Massachusetts, United States.
authors.forename: Seok Hyun
authors.initials: SH
authors.lastname: Yun
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D003315:Cornea / Q000503:physiopathology*; D016039:Corneal Transplantation; D057111:Descemet Stripping Endothelial Keratoplasty; D018450:Disease Progression; D055119:Elastic Modulus / Q000502:physiology*; D054459:Elasticity Imaging Techniques; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D021621:Imaging, Three-Dimensional; D007640:Keratoconus / Q000175:diagnosis / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D018613:Microscopy, Confocal / Q000379:methods*; D008875:Middle Aged
keywords: Brillouin microscopy; corneal biomechanics; keratoconus