Post on 19-Dec-2015
transcript
Influence of Keratoplasty Technique on Corneal Biomechanical Properties in Keratoconus
Hans R Vellara, Noor Q Ali, Charles NJ McGhee, Dipika V Patel
Department of OphthalmologyUniversity of Auckland, New Zealand
nz national eye centre
The authors have no financial interests to disclose
Biomechanics
Elastic
Viscous
The cornea is viscoelastic
Biomechanics & Keratoconus
Keratoconus – underlying biomechanical failure
Penetrating Keratoplasty (PKP)
Deep Anterior Lamellar Keratoplasty (DALK)
End stage management options
Aims
• To determine if corneal biomechanics are closer to normal after corneal transplantation
• To determine the effect of corneal transplantation type on corneal biomechanical properties
Methods
• Prospective cross sectional study• 33 PKP and 23 DALK eyes
• Exclusion: <3/12 post-surgerycorneal oedemacurrent rejection raised IOP
• Examinations:Slit-lampPentacam tomographyAS – OCTCorVis ST
CorVis ST
What is it?• Air Tonometer• Ultra high speed Scheimpflug
camera
How does it work?• Air puff indents cornea• Video 4333 frames/sec• Calculates a range of output
measurements• Parameters describe in vivo biomechanics
CorVis ST - Parameters• Applanation1
• Time• Length• Velocity
• Highest Concavity• Deformation
Amplitude (DA)• Radius of Curvature
(RoC)• Peak Distance (PD)
• Applanation2• Time• Length• Velocity
Comparison of above parameters between PKP and DALK
ResultsMean PKP DALK p-valueAge (years): 35.6 37.5 0.61Time from surgery (months): 83.2 91.1 0.42Corneal thickness (µm): 534 594 <0.001Peak distance (PD) 4.8 3.4 0.03
All other CorVis ST parameters: p-value (>0.05)
CorVis ST – PKP vs. DALK
Two corneas overlapped at highest concavity (similar CCT and IOPs).
Results – See attached videoPKP vs. DALK vs. Normal
PKP vs. DALK vs. KCDA 1.16 1.18 1.38RoC 7.20 6.31 4.79
3 corneas overlapped at highest concavity. The deformation profiles are very similar.
p-value: <0.05
3 corneas overlapped at highest concavity. The deformation profile of the keratoconic cornea (green) differs from the others.
Conclusion
• Corneal biomechanical properties after PKP and DALK are similar
• However, the difference in PD may indicate a more viscous cornea after DALK
• Biomechanical properties after corneal transplant for keratoconus resemble normal corneas