1. Laser Bridge AK: Laser Bridge AK: Novel Architecture for Laser Astigmatic Keratotomy Comparison and Validation of Patient-Specific Computational Modeling Anita Nevyas-Wallace, MD Nevyas Eye Associates, Bala Cynwyd, Pennsylvania Clinical Associate, University of Pennsylvania Dept. of Ophthalmology Cynthia J. Roberts, PhD Professor of Ophthalmology & Biomedical Engineering; Martha and Milton Staub Chair for Research in Ophthalmology, The Ohio State University Harald P. Studer, PhD Integrated Scientific Services, Port, Switzerland

2. Financial Disclosures Anita Nevyas-Wallace, MD Varitronics, Inc: C, Bausch + Lomb, Inc: C, Eye IC: S Cynthia J. Roberts, PhD Oculus: C, Ziemer Ophthalmic Systems: C, Carl Zeiss Meditec: research funding, Euclid Corp: travel funds Harald P. Studer, PhD Integrated Scientific Services: E

3. Note greater elevation of center of AK, compared with ends Pre-op Post-LRI Even FS AK’s show problems Even AK’s of uniform depth show greater effect at the center than at the ends, leading to induced HOA and variable predictability This is because an incision’s ends are stabilized by intact cornea; its center is point of greatest relaxation Why?

4. Making the incision deeper at the ends, shallower at the center – mitigates the overcorrecting effect of the AK’s center – while augmenting the effect of its ends The Laser “Bridge” AK

5. Purpose: To build and to validate a patient-specific computational model of a novel astigmatic keratotomy (AK) incision architecture, the Laser Bridge AK, and to compare results model predicts for Laser Bridge AK with those predicted for uniform AK

6. Methods Finite element modeling simulated the novel architecture of Laser Bridge AK in a custom mathematical function which considered corneal incompressibility and nonlinearity, fiber-induced anisotropy, and inhomogeneity. The incision is nasal, and clearly has opened a gap in the cornea in this image. The gap leads to deformations on the corneal surface. Stress distribution in the FE model of patient: Colors represent van Mises stress in Mega-Pascals (Mpa). The small squares forming the volume mesh are the finite elements.

7. Methods A 76 year old man underwent phaco/IOL with nasal AK. A DuoTrak blade was used to create a 9mm optical zone nasal AK 150 microns shallower centrally than at its ends. Incision morphology was measured via Slit Lamp Photography and Optical Coherence Tomography. Pre-op patient specific Galilei tomography was imported into Optimeyes software. The simulated incisions’ result was calculated with ABAQUS. Post-operative results were compared to the simulated post-operative model for validation.

8. SimK steep43.03D SimK flat42.35D Astigmatism0.68D@23° Central Curvature 42.83D Spherical Ab0.09um Coma0.14um Trefoil0.10um RMS HOA0.10um SimK steep43.07D SimK flat42.30D Astigmatism0.78D@14° Central Curvature 42.80D Spherical Ab0.16um Coma0.14um Trefoil0.03um RMS HOA0.09um Simulation result Clinical follow-up (7 month)

9. Results The patient’s astigmatism on refraction was reduced from 1.75D against the rule to 0.25D with the rule. The simulated outcome was compared with the postoperative Galilei corneal tomography. The simulated outcome showed a close match to the measured post-operative results. Compared with the model’s predicted outcome for a traditional AK of uniform depth and thickness, the Laser Bridge AK was predicted to have  substantially less induced higher order aberrations, as well as  greater astigmatic effect.

10. Thickness of Incision Ends [μm] Depth of Incision Center [%] Previous Theoretical Studies: Laser Bridge AK induced up to 83% Less Coma than Uniform AK Coma induced [µm] Traditional Laser Bridge AK Induced up to 83% Less Coma than Uniform AK

11. Greater Astigmatic Correction despite inducing less HOA Laser Bridge AK Achieved up to 15% Greater Astigmatic Correction than a uniform incision, despite inducing less HOA Astigmatic Correction [Diopters] Thickness of Incision Ends [μm] Depth of Incision Center [%] ↑ 15%

12. Conclusions Patient-Specific Finite Element Modeling of the Laser Bridge AK was validated for the patient modeled. Our novel incision architecture for FS laser AK – Laser Bridge AK Incisions with shallower center – produced optimal simulation results with – greater correction of astigmatism – substantially less induction of HOA Our ability to control incision architecture may be the key contribution of the FS laser to potential improvement of both UCVA and BSCVA Future studies include comparing different novel incision architectures