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