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