title: An in vitro intact globe expansion method for evaluation of cross-linking treatments.
abstract: OBJECTIVE
  To measure the tissue mechanical response to elevated intraocular pressure (IOP) using intact globe expansion of rabbit eyes. This method examined rabbit kit (2-3 weeks old) eyes as a model for weakened tissue and evaluated riboflavin/UVA and glyceraldehyde cross-linking treatments.
  
  
  METHODS
  The ocular shape of enucleated eyes was photographed during a 24-hour period while a controlled IOP was imposed (either low IOP = 22 mm Hg or high IOP = 85 mm Hg). Untreated controls consisted of kit eyes tested at both low- and high IOP and adult eyes tested at high IOP. Treated kit eyes (dextran controls, riboflavin/UVA treatment of the cornea, and glyceraldehyde treatment of the entire globe) were tested at high IOP.
  
  
  RESULTS
  Low IOP elicited negligible creep of the sclera and very gradual creep of the cornea. In contrast, high IOP induced up to an 8% strain in the sclera and a 15% strain in the cornea of rabbit kit eyes. The expansion of adult eyes was less than one third that of kit eyes at the same, high IOP. Riboflavin/UVA treatment of corneas reduced expansion compared with that in both dextran-treated and untreated control corneas. Glyceraldehyde treatment prevented expansion of the cornea and sclera.
  
  
  CONCLUSIONS
  The intact globe expansion method (GEM) imposes a loading geometry comparable to in vivo conditions and can quantify changes in mechanical stability as a function of testing conditions (e.g., IOP, tissue maturation, and therapeutic cross-linking) with small sample sizes and small variability. Rabbit kit eyes provide a model of weak tissue suitable for screening treatments that strengthen the cornea and sclera.
authors.affiliation: Department of Engineering and Applied Science, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Mattson
authors.forename: Joyce
authors.initials: J
authors.lastname: Huynh
authors.forename: Meredith
authors.initials: M
authors.lastname: Wiseman
authors.forename: Marco
authors.initials: M
authors.lastname: Coassin
authors.forename: Julia A
authors.initials: JA
authors.lastname: Kornfield
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Schwartz
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001696:Biomechanical Phenomena; D003094:Collagen / Q000378:metabolism*; D003315:Cornea / Q000187:drug effects* / Q000378:metabolism; D004547:Elastic Tissue / Q000502:physiology; D005260:Female; D005985:Glyceraldehyde / Q000627:therapeutic use; D007429:Intraocular Pressure; D008297:Male; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011817:Rabbits; D012256:Riboflavin / Q000494:pharmacology*; D012590:Sclera / Q000187:drug effects* / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D017319:Photosensitizing Agents; D005985:Glyceraldehyde; D003094:Collagen; D012256:Riboflavin