title: Ultrastructural analysis of collagen fibrils and proteoglycans in keratoconus.
abstract: OBJECTIVE
  To investigate ultrastructural alterations in the distribution of collagen fibrils (CFs) and proteoglycans (PGs) in the keratoconus cornea.
  
  
  METHODS
  Four normal corneas (donor age 24-75 years) and four severe and one mild keratoconus corneas (donor age 24-47 years) were fixed in 2.5% glutaraldehyde containing 0.05% cuprolinic blue dye for electron microscopy. Analyses were carried out on approximately 39 000 CF and 66 000 PG filaments in the anterior, middle and posterior stroma, using analySIS soft imaging software.
  
  
  RESULTS
  In severe keratoconus, stromal lamellae were seen to undulate in most regions, whereas in mild keratoconus only the middle and posterior lamellae were affected. In keratoconus corneas the mean diameter and interfibrillar spacing of CFs was reduced in all zones (p < 0.0001) and the CF and PG number density and area fractions were significantly increased (p < 0.0001) compared with in normal corneas and were higher (p < 0.0001) in the corneas with severe keratoconus than in that with mild keratoconus. The lamellae contained microfibrils (8-9 nm wide) and, in addition, PGs embedded within CFs. Degenerate keratocytes containing PGs were found in all keratoconus corneas.
  
  
  CONCLUSIONS
  These studies suggest that as keratoconus progresses, the PG content of the stroma increases, whereas fibril diameter is reduced. The altered stromal content of PGs may influence CF diameters and their organization in keratoconus, weakening lateral cohesion and resulting in significant disorder of CF packing.
authors.affiliation: School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK. akhtars@ksu.edu.sa
authors.forename: Saeed
authors.initials: S
authors.lastname: Akhtar
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Bron
authors.forename: Sachin M
authors.initials: SM
authors.lastname: Salvi
authors.forename: Nicolas R
authors.initials: NR
authors.lastname: Hawksworth
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Tuft
authors.forename: Keith M
authors.initials: KM
authors.lastname: Meek
mesh_terms: D000328:Adult; D000368:Aged; D003094:Collagen / Q000378:metabolism* / Q000648:ultrastructure*; D003315:Cornea / Q000378:metabolism / Q000648:ultrastructure; D003319:Corneal Stroma / Q000378:metabolism / Q000648:ultrastructure; D018450:Disease Progression; D006801:Humans; D007640:Keratoconus / Q000378:metabolism* / Q000473:pathology*; D020894:Microfibrils / Q000648:ultrastructure*; D008854:Microscopy, Electron; D008875:Middle Aged; D011509:Proteoglycans / Q000378:metabolism / Q000648:ultrastructure*; D012720:Severity of Illness Index; D014018:Tissue Distribution; D055815:Young Adult
chemical_list: D011509:Proteoglycans; D003094:Collagen