title: Evaluation of lamina cribrosa and peripapillary sclera stiffness in pseudoexfoliation and normal eyes by atomic force microscopy.
abstract: OBJECTIVE
  Pseudoexfoliation (PEX) syndrome is a systemic disorder of the elastic fiber system that can lead to PEX glaucoma. Elastotic alterations in the lamina cribrosa (LC) of PEX eyes suggested biomechanical implications predisposing to pressure-induced optic nerve damage. In this pilot study, the stiffness of LC and peripapillary sclera (ppSC) in eyes with and without PEX syndrome were analyzed by atomic force microscopy (AFM) nanoindentation.
  
  
  METHODS
  Unfixed cryosections (5-μm thick) were prepared from the optic nerve heads (ONH) of three donor eyes with PEX syndrome and three age-matched control eyes. AFM force mapping was performed in selected regions of the central, midperipheral, and peripheral LC and the ppSC using a spherical cantilever tip. To determine the local Young's modulus of elasticity (YME) as a measure of tissue stiffness, force curves were acquired and analyzed using the spherical Hertz model.
  
  
  RESULTS
  For the LC, the median YME values calculated from single stiffness maps averaged 17.2 (±2.7) kPa in normal eyes and 10.1 (±1.4) kPa in PEX eyes, indicating a significant PEX-related decrease in stiffness by over 40% (P < 0.01). The corresponding YME values for the ppSC, which revealed a 9-fold higher tissue stiffness than in the LC, averaged 158.3 (±59.8) kPa for control and 85.8 (±16.9) kPa for PEX samples.
  
  
  CONCLUSIONS
  AFM was proven suitable for determining the stiffness of ONH tissues, encouraging further large-scale analyses. The marked decrease in stiffness, implying an increased deformability of the ONH in PEX eyes, may reflect an inherent tissue weakness rendering these eyes more vulnerable to glaucomatous damage.
authors.affiliation: Institute of Applied Physics, Friedrich-Alexander-University of Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Braunsmann
authors.forename: Christian M
authors.initials: CM
authors.lastname: Hammer
authors.forename: Johannes
authors.initials: J
authors.lastname: Rheinlaender
authors.forename: Friedrich E
authors.initials: FE
authors.lastname: Kruse
authors.forename: Tilman E
authors.initials: TE
authors.lastname: Schäffer
authors.forename: Ursula
authors.initials: U
authors.lastname: Schlötzer-Schrehardt
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D004548:Elasticity / Q000502:physiology; D017889:Exfoliation Syndrome / Q000473:pathology*; D006801:Humans; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D008875:Middle Aged; D009898:Optic Disk / Q000648:ultrastructure*; D009901:Optic Nerve Diseases / Q000473:pathology*; D010865:Pilot Projects; D012590:Sclera / Q000648:ultrastructure*