1. Ahmed El-Massry, M.D. Professor of Ophthalmology - Faculty of Medicine University of Alexandria Egypt long-Term Results of Corneal Biomechanical Changes After Refractive Laser Procedures The authors have no Financial interest in the subject matter of this poster Nader Bayomi M.D.Sherif Tolees M.D.

2. Corneal Hysteisis (CH) is a phenomenon results from the dynamic nature of the air pulse & viscous damping inherited in the cornea. Corneal resistance factor (CRF) is a measurement of the cumulative effects of both the viscous and elastic resistance encountered by the air jet while deforming the corneal surface.

3. To evaluate the corneal biomechanical changes (Corneal Hysterisis “CH” and Corneal resistance factor “CRF”) after more than one year of corneal Laser refractive surgeries.

4. Ocular response analyzer was used to measure Corneal hysterisis (CH), Corneal resistance factor (CRF), Goldmann- correlated Intraocular pressure (IOPg) and corneal compensated IOP (IOPc) before and after three months, and one year of different thickness flap created in laser correction procedures.

5. Group 1 (50 eyes) Lasik was done using the M2 micro-keratome creating a flap thickness of 130 micron. Group 2 (50 eyes) Epilasik was done using the Moria Epi-k microkeratome that separates the epithelial sheet in one mass from the Bowman’s membrane. Group 3 (50 eyes) Lasik was done using the 100 microns flap thickness using the OUP-SBK microkeratome of Moria. All eyes were subjected to laser ablation and were divided into 3 groups: Study design (cont.)

6. All eyes were subjected to the usual screening investigations and ORA: -Preoperatively. - Preoperatively. - One week postoperatively. - One week postoperatively. - One month postoperatively. - One month postoperatively. - Three months postoperatively. - And one year after the laser refractive procedures. - And one year after the laser refractive procedures. ahmad.elmassary@gmail.com

7. Preop. CH, and postop. 1 week, 1 month, 3 months and 1 year CH in the studied groups. Results CH_1Y

8. Results CRF_1Y Preop. CRF, and postop. 1 week, 1 month, 3 months and 1 year CRF in the studied groups.

9. Corneal Hysterisis decreased after 3 months one year 3 months one year In Group 1: (Lasik 130 micron flap)35% 35% In Group 2: (Epilasik)18% 18% In Group 3: (Thin Flap lasik) 23% 23% Results

10. Corneal biomechanical changes decrease after all refractive surgery procedures by three months and remain stable till after one year. Conclusion

11. Both Epi-lasik with discarding the flap, and Lasik using OUP-SBK micro-keratome (100micron thickness) are more safe techniques for CH and CRF, after more than one year with statistically significant stable Corneal biomechanical properties in comparison to 130 micron flap lasik. Conclusion

12. Epilasik is a perfect surface ablation procedure that also keeps the CH and CRF postoperatively by three months and one year (  18%), better than thin flap Lasik (  23%), which is also better than 130 micron flap Lasik (  35%). The corneal resistance factor parameter may be more useful than CH parameter in assessing biomechanical changes resulting from lasik.