Ahmed El-Massry, M.D.Professor of Ophthalmology - Faculty of Medicine

University of AlexandriaEgypt

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.

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.

To evaluate the corneal

biomechanical changes

(Corneal Hysterisis “CH” and

Corneal resistance factor “CRF”)

after more than one year of corneal

Laser refractive surgeries.

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.

Group 1 (50 eyes)Group 1 (50 eyes)Lasik was done using the M2 micro-keratome Lasik was done using the M2 micro-keratome

creating a flap thickness of 130 micron.creating a flap thickness of 130 micron.

Group 2 (50 eyes)Group 2 (50 eyes)Epilasik was done using the Moria Epi-k Epilasik was done using the Moria Epi-k

microkeratome that separates the epithelial sheet in microkeratome that separates the epithelial sheet in one mass from the Bowman’s membrane.one mass from the Bowman’s membrane.

Group 3 (50 eyes)Group 3 (50 eyes)Lasik was done using the 100 microns flap thickness Lasik was done using the 100 microns flap thickness

using the OUP-SBK microkeratome of Moria.using the OUP-SBK microkeratome of Moria.

All eyes were subjected to laser ablation and weredivided into 3 groups:

Study design (cont.)Study design (cont.)

All eyes were subjected to the usual screening All eyes were subjected to the usual screening investigations andinvestigations andORA:ORA:

-- Preoperatively.Preoperatively.

- One week postoperatively.- One week postoperatively.

- One month postoperatively.- One month postoperatively.

- Three months postoperatively.- Three months postoperatively.

- And one year after the laser refractive procedures.- And one year after the laser refractive procedures.

ahmad.elmassary@gmail.com

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

Results

CH_1Y

Results

CRF_1Y

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

Corneal Hysterisis decreased after Corneal Hysterisis decreased after

3 months3 months one yearone year

In Group 1: (Lasik 130 micron flap)In Group 1: (Lasik 130 micron flap) 35% 35% 35% 35%

In Group 2: (Epilasik)In Group 2: (Epilasik) 18% 18% 18%18%

In Group 3: (Thin Flap lasik) In Group 3: (Thin Flap lasik) 23% 23% 23%23%

Results

Corneal biomechanical changes decrease after

all refractive surgery procedures by three months and remain

stable till after one year.

Conclusion

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

Conclusion

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.