ICT – ICT – Intraoperative Corneal TopographyIntraoperative Corneal Topographyfor image registration purposesfor image registration purposes
S.SchründerS.Schründer
Model eye
6mm optical zone
8mm cornealradius
6mm pupil, 4mm below apex
5mm to rotation axis
12mm radiusbulbus
Tilted eye
Motivation
Aberrometer
Ablation pattern
Tilted eye
1st wrong pattern
TreatmentDiagnosis
Ablation pattern
Tilted eye
2nd wrong pattern
Eyetracker
Solution
Registration in 3d space
Requirement
3d objects
Height map pre ablation*
*Difference to 8.4mm sphereRange 100µm
Height map post ablation*
*Difference to 8.7mm sphereRange 100µm
Fine registration: Iterative Closest Point
Find corresponding 3d points (via Hough tables)Minimize their distance
Distance Minimization:1. Levenberg-Marquardt
for fast convergence2. Simmulated annealing
to overcome local minima
Registration points area
Detected flap edge
Difference map after registration
7.5mm circleRange 105µm
Line scans
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
1 2 3 4 5 6 7 8 9 10
horizontal cut
vertical cut
100mm sphere
Dimensions in mm
3d Flap thickness
9.5mm circleRange 290µm
Line scans
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0 1 2 3 4 5 6 7 8 9 10 11 12
vertical cut
horizontal cut
Dimensions in mm
Next steps
Rigid incorporation into a laser system
Extended clinical trials
Stand alone device
Centered cornea
0.5mm lateral shift
Corresponding tilt
0.22mm decentration
Linear function*
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
lateral shift of tilted movement [mm]
dece
ntra
tion
[mm
]
*8mm corneal radius, 4mm apex/pupil, 13mm apex/rotation axis
Andreas DankertAndreas Dankert
Hendrik FuchsHendrik Fuchs
Saso SpasovskiSaso Spasovski
Coworkers at BioShape
Thank you.Thank you.
bioshape.combioshape.com
