ICT – Intraoperative Corneal Topography for image registration purposes S.Schründer

Model eye 6mm optical zone 8mm corneal radius 6mm pupil, 4mm below apex 5mm to rotation axis 12mm radius bulbus

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 sphere Range 100µm

Height map post ablation* *Difference to 8.7mm sphere Range 100µm

Fine registration: Iterative Closest Point Find corresponding 3d points (via Hough tables) Minimize their distance Distance Minimization: 1.Levenberg-Marquardt for fast convergence 2.Simmulated annealing to overcome local minima

Registration points area Detected flap edge

Difference map after registration 7.5mm circle Range 105µm

Line scans Dimensions in mm

3d Flap thickness 9.5mm circle Range 290µm

Line scans 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* *8mm corneal radius, 4mm apex/pupil, 13mm apex/rotation axis

Andreas Dankert Hendrik Fuchs Saso Spasovski Coworkers at BioShape

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