Marija Antičić, Maja Bohač, Mateja Končarević, Alma Biščević, Sunčana Kovačić, Nikica Gabrić

Specialty Eye Hospital “Svjetlost”

School of Medicine, University of Rijeka

20th ECSRS Winter Meeting Athens

Comparison of Laser In Situ Keratomileusis Flaps Created by 3

Femtosecond Lasers

DISCLOSURE: None of the authors have a financial interest in any of the products or devices noted

FEMTOSECOND LASERS

• The prototype of the first ophtalmic surgical FS laser system was designed and constructed by Dr Juhasz and his associates at the University of Michigan College of Engineering Center for Ultra-fast Optical Scienses (CUOS) in the early 1990s 1

• Have changed refractive surgery in the last 15 years since the market release of the Intralase Femtosecond laser (Abbot Medical Optics, Il, USA) in 20011

• The bladeless flap creation rapidly gained popularity because of its safety, fast recovery and excellent results2

1. Soong HK, Malta JB, Femtosecond lasers in ophtalmology. Am J Ophtalmol 147, 189-197 (2009)2. Durrie DS, Kezirian GM, Femtosecond laser versus mechanical microkeratome flaps in wavefront-guided laser in situ

keratomileusis: prospective contralatelar study. J Cataract Refractive Surg 31, 120-6 (2005)

Why Femtosecond lasers in corneal surgery?

• Ultra-short pulse duration (10-15 sec.) has the ability to deliver laser energy with minimal collatelar damage to the adjacent tissue (1μm).

High focus quality inside the cornea

• Precisely cut corneal flaps are essential for successful LASIK.

• Create uniform thickness planar configuration flaps; microkeratomes create flaps with less uniform thickness.

• The creation of a flap of intended thickness is crutial for obtaining an appropriate residual stromal thickness.

Mecanism of action: Photodistruption

• FSL energy is absorbed by the tissue, resulting in plasma formation.

• The plasma of free electrons and ionized molecules rapidly expands creating cavitation bubbles.

• The force of the cavitation bubble creation separates the tissue.

• Multiple pulses are applied next to each other to create a cleavage plane and ultimately the LASIK flap.

Advantages:

• Reduced incidence of flap complications like buttonholes, free caps, irregular cuts etc.

• Control over flap diameter and thickness, side cut angle, hinge position and lenght.

• Increased precision with improved flap safety and better thickness predictability.

• Capability of cutting thinner flaps to accommodate thin corneas and high refractive errors.

• Stronger flap adherence.• The ability to retreat immediately if there is incomplete FS laser

ablation.• Decreased incidence of epithelial ingrowth and dry eye.• Better contrast sensitivity• Less increase in IOP required

Disadvantages:

• Opaque bubble layer (OBL)

• Transient light sensitivity syndrome (TLSS)

• Increased difficulty in lifting the flap if retreatment is requred after that (because of good adherence)

• Increased cost.

Femtosecond lasers used in our study:

• Intralase FSTM 150KHZ (Abbot Medical Optics, Abbott Park, Illinois)

• Femto LDVTM (Ziemer Group, Port, Switzerland)

• VisuMax Femtosecond System® (Carl Zeiss Meditec, Jena, Germany)

Technical Features of Femtosecond Laser Devices for Flap Creation

Feature Intralase IFS Ziemer LDV Carl Zeiss VisuMax

Puls Rate 150 KHZ 1MHZ 500 KHZ

Pulse duration 500 fs 200 -300 fs 400 (?) fs

Spot size 1-5m 2 m 1 m

Pulse energy 500-1300 nJ 100 nJ 300 nJ

Concept Amplified Oscillator Amplified

Additional feature Greatest number of treated eyes

Portable, Low energy FlexSmile

Suction Manual Computer controlled within handpiece

Computer controlled low Pressure

Laser-Cornea Coupling Flat Flat Curved

Customizable features High Very limited Very high

Purpose• To compare corneal flap morphology created by the -Intralase FS (femtosecond group 1) -Ziemer LDV (femtosecond group 2) -VisuMax (femtosecond group 3)• The patients were divided into 3 groups based on the

device used for flap creation.• Comparative case series, on patients with myopia and

myopic astigmatism who were consecutively scheduled for bilateral LASIK treatment –from February 2013 to July 2015.

Mean ± SD

Group 1 Group 2 Group 3

Characteristic Intralase IFS Ziemer LDV VisuMax

No. eyes 82 82 82

Mean age, yr 25.0±5.1 26±5.7 26±5.5

Mean SE, D -6.4±2.2 -6.7±2.8 -6.5±2.5

Mean CCT, μm 560±25,6 564±28.9 559±27,3

Mean corneal curvature, D

44±1.8 43.5±1.4 43.8±1.7

CCT, central corneal thickness; SE, spherical equivalent refraction

PREOPERATIVE DEMOGRAPHICS

We evaluated:• Central flap thickness• Mean flap thickness• Meridian flap uniformity• Difference between the mean central and mid-peripheral

flap thickness 2 mm in the horisontal and vertical plane • Flap thickness predictability (mean deviation between the

achieved and attempted flap thickness)• OCT (Carl Zeiss Meditec AG, Jena Germany) for assessing

flap regularity, uniformity and predictability• Flap thickness was determined at 10 points, 3 months

postoperatively• Intented flap thickness was 110 μm

SURGICAL PROCEDURE

Characteristic Intralase IFS Ziemer LDV VisuMaxFlap thickness, μm 110 110 110

Flap diameter, mm 9,0 9,5 9,0

Angle side cut, degree 90 28 Fixed 90

Pattern raster Raster/mechanicals

spiral

Raster energy 0,45 uJ/Pulse 0,1 uJ/Pulse 0,4 uJ/Pulse

hinge superiorly superiorly superiorly

SURGICAL PROCEDURE

Matherials and Methods• Measurements of the flaps in the 0-, and 90- degree lines

0o

45o

90o

135o

180o

225o 270o 315o

Statistical analyses were performed using statistical software MedCalc for Windows, version 11.5.1.0 (MedCalc Software, Mariakerke, Belgium)

ResultsCentral and Mean Flap Thickness

Central mean SD

1. Ziemer LDV 94,04 3,20

2. VisuMax 105,58 15,55

3. Intralase IFS 111,0 11,50

Kruskal Wallis test: P<0.001, post hoc test (p<0,05, 1 vs. 2 and 3, 2 vs 1, 3 vs 1)

Mean flap mean SD

1. ZiemerLDV 110,78 11,29

2. VisuMax 105,68 16,5

3. Intralase IFS 107,44 10,76

Kruskal Wallis test: P<0.001, post hoc test (p<0,05, 1 vs. 2 and 3, 2 vs 1, 3 vs 1)

ZIEMER LDV (mean +/- SD )

Kruskal Wallis test P<0,001Flaps in femtosecond laser Ziemer LDV had the assymerty between the center and periphery.These findings are consistent with other authors. 3

3. Hyunseok Ahn, MD, Jin-Kook Kim et al. Comparison of laser in situ keratomileusis flaps created by 3 femtosecond lasers and a microkeratome. J Cataract Refract Surg; 37:349–357 (2011).

VisuMax (mean +/- SD )

Kruskal Wallis test P= 0,609

The disparity between center and periphery flap thickness was not statistically significant.

Intralase IFS (mean +/- SD )

Kruskal Wallis test P= 0,323

The disparity between center and periphery flap thickness was not statistically significant.

Meridian flap uniformity

Mean(SD)

90 degrees 180 degrees P

1. ZiemerLDV 110,73 (11,31) 110,83 (11,30) 0,981

2. VisuMax 107,46 (16,67) 103,9 (16,41) 0,365

3. Intralase IFS 108,50 (11,05) 106,38 (11,42) 0,596

Meridian flap uniformity measured at the 10 measurement points at 90- and 180- degrees were uniform and regular for each femtosecond device.

The mean center vs. mid-periphery 2 mm in the horisontal and vertical plane

Central SD cent Mid perif SD perif P

1. ZiemerLDV 94,048 3,20 108,27 4,63 <0,001

2. VisuMax 105,58 15,55 108,125 17,09 0,667

3. Intralase IFS 111,00 11,5 106,36 10,37 0,103

Mann Whitney U test

0o

90o

Results

Ziemer LDV Intralase IFS VisuMax0

2

4

6

8

10

12

14

16

9.29.6

13.5

Flap thickness Predictability(the mean deviation between the achieved and attempted flap thickness)

Diffe

renc

e (μ

m)

ResultsFlap thickness Accuracy

(the mean deviation between the achieved and attempted flap thickness)

Percentage %

Percentage (%)μm <5 5-10 >10 P

1. ZiemerLDV 39 30 31 0,417

2. VisuMax 40 36,7 23,3 0,496

3. Intralase IFS 40,8 30,9 27,3 0,385

Conclusions• Although the central flap thickness created by the Ziemer

LDV was less than that created by the Intralase and VisuMax, measurements of 3 femtosecond lasers were close to the intended thickness.

• The Femto-LDV system was the most predictable in terms of flap creation (intended versus measured flap thickness).

• Flaps in the Visumax group had the least difference between the mean peripheral and the central flap thickness.

• Flap morphology differed according to the system used.

THANK YOU FOR YOUR ATTENTION