title: Changes in corneal biomechanics in patients with keratoconus after penetrating keratoplasty.
abstract: OBJECTIVE
  To examine the biomechanical properties of keratoconic eyes following penetrating keratoplasty and to compare results with the biomechanical characteristics of manifest keratoconus, forme fruste keratoconus and normal eyes as measured with the Reichert ocular response analyzer (ORA).
  
  
  METHODS
  This retrospective analysis comprised a total of 169 eyes: 34 eyes with forme fruste keratoconus (group FF), 36 eyes with manifest keratoconus (Group KC), 36 eyes that have undergone penetrating keratoplasty (Group PK) and a control group of 63 normal eyes (Group N). Corneal hysteresis (CH), corneal resistance factor (CRF), corneal compensated intraocular pressure, and Goldmann correlated intraocular pressure were measured by ORA. Central corneal thickness was calculated by the integrated handheld ultrasonic pachymeter of the ORA. The statistical analysis focused on CH and CRF changes among the 4 groups.
  
  
  RESULTS
  When compared with normal eyes, mean CH and CRF values were found significantly lower in all groups (P < 0.05). Mean CH values were 8.19 ± 1.49 mm Hg in Group KC, 9.21 ± 1.38 mm Hg in Group FF, 10.16 ± 1.93 mm Hg in Group PK, and 11.43 ± 1.52 mm Hg in normal eyes (Group N). Although there was not a significant difference in mean CH values between Groups PK and FF (P = 0.072), the difference was significant between Groups KC as well as FF and Groups KC and PK (P < 0.05). Mean CRF values were found as 6.79 ± 1.81 mm Hg (Group KC), 8.21 ± 1.64 mm Hg (Group FF), 9.94 ± 2.34 mm Hg (Group PK), and 11.53 ± 1.83 mm Hg in Group N. The difference was statistically significant among all groups (P < 0.05).
  
  
  CONCLUSIONS
  Penetrating keratoplasty has a beneficial effect on corneal biomechanics in keratoconic eyes. CH and CRF parameters approach the range of normal eyes after corneal transplantation.
authors.affiliation: Department of Ophthalmology, Yeditepe University Medical Faculty, Yeditepe University, Istanbul, Turkey. meldayen@hotmail.com
authors.forename: Nursal Melda
authors.initials: NM
authors.lastname: Yenerel
authors.forename: Raciha Beril
authors.initials: RB
authors.lastname: Kucumen
authors.forename: Ebru
authors.initials: E
authors.lastname: Gorgun
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D003187:Compliance; D003315:Cornea / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D007429:Intraocular Pressure; D007640:Keratoconus / Q000601:surgery*; D015948:Keratoplasty, Penetrating; D008875:Middle Aged; D011184:Postoperative Period; D012189:Retrospective Studies; D014463:Ultrasonography