How to get a good centration during SMILE?

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Denis Potter
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1 How to get a good centration during SMILE? Walter Sekundo Apostolos Lazaridis Department of Ophthalmology, Philipps University of Marburg, Germany. Prof.Sekundo is a consultant Carl Zeiss Meditec AG

Purkinje reflex ReLEx Self-centration: the patient is asked to observe

2 Centration and Tracking Femtolasik Aktive eyetracker Logged on at the pupil centre Can be adjusted by the surgeon according to the 1st Purkinje reflex ReLEx Self-centration: the patient is asked to observe a blinking light during the suction and the surgery Excimer laser VisuMax fs-laser

Mental state of the surgeon Femtolasik ReLEx www.

de Excimer laser: I am in charge using sophisticated

3 Mental state of the surgeon Femtolasik ReLEx Excimer laser: I am in charge using sophisticated machinery VisuMax fs-laser: I, the surgeon, have to (partially) rely on the patient

4 Patient data Groups Patients Mean Age Total Eyes OD OS Gender Full Correction Eyes Mean SEQ (Dpt) Mean Cylinder (Dpt) Mean central Simulated Keratometer readings (Dpt) (n=1.3375) ReLEx (22 to 55) (-1.25 to -10) (0 to -4.0) fs-lasik (23 to 65) (-0.75 to -10) -1 (0 to -4.5) Surgical data Groups Mean SEQ of the correction (Dpt) Mean Cylinder of the correction (Dpt) Mean Flap/Cap Thickness (μm) Mean Flap/Cap Diameter (mm) Mean Lenticule Thickness/ Ablation Depth (μm) Mean Lenticule/ Ablation Diameter (mm) ReLEx (-1.25 to -10) (0 to -4.0) 118 (100 to 120) 7.8 (7.5 to 8.0) 120 (48 to 164) 6.7 (6.2 to 7.0) fs-lasik (-0.75 to -10) (0 to -4.5) 113 (100 to 120) 8.36 (8.0 to 8.5) 103 (22 to 165) 6.32 (6 to 6.75) Lazaridis et al JRS, 2014

Methods Centration Analysis by pachymetry differential maps: Distance of the thickest point from apex (vertex*) and pupil centre ReLEx Smile (OD) Mean Spherical Equivalent of the Correction -4.

5 Methods Centration Analysis by pachymetry differential maps: Distance of the thickest point from apex (vertex*) and pupil centre ReLEx Smile (OD) Mean Spherical Equivalent of the Correction Dpt Decentration from Apex: 0.297mm Decentration from Pupil centre: mm Thickest point 1. Find the thickest point (x,y) on the pachymetry diff. map after 3 measurements 2. Estimate the distance between the thickest point and pre-op corneal apex 3. Estimate the distance between the thickest point and pre-op pupil centre as defined by Pentacam using Pythagorean theorem (d= x²+y²) * Close approximation of the visual axis. Pande M, Hilman JS, Ophthalmology 1993

Example Femto-Lasik Fs-LASIK (OD) Mean Spherical Equivalent of the Correction - 5.

421 Thickest point Fs-LASIK (OS) Mean Spherical Equivalent of the Correction - 5.

6 Example Femto-Lasik Fs-LASIK (OD) Mean Spherical Equivalent of the Correction Dpt Decentration from Apex: mm Decentration from Pupil Centre: Thickest point Fs-LASIK (OS) Mean Spherical Equivalent of the Correction Dpt Decentration from Apex: mm Decentration from Pupil Centre : mm Thickest point

Example ReLEx ReLEx Smile (OD) Mean Spherical Equivalent of the Correction - 6.75 Dpt Decentration from Apex: 0.103 mm Decentration from Pupil Centre: 0.

7 Example ReLEx ReLEx Smile (OD) Mean Spherical Equivalent of the Correction Dpt Decentration from Apex: mm Decentration from Pupil Centre: Thickest point ReLEx Smile (OS) Mean Spherical Equivalent of the Correction Dpt Decentration from Apex: mm Decentration from Pupil Centre: Thickest point

8 Results Decentration in relation to the corneal apex (0,0) 1.50 OD, OS 1.50 OD, OS ReLEx Mean Decentration: fs-lasik Mean Decentration: 0.516

9 Results Decentration in relation to the pupil centre (0,0) 1.50 OD, OS 1.50 OD, OS ReLEx Nasalisation of the fixation in relation to the pupil centre = positive angle κ Mean Decentration: fs-lasik Centration is randomly distributed Mean Decentration: 0.452

10 Results: Summary Decentration (mm) from pupil centre ,2 0,2-05 0,5-1 >1 perfect good acceptable poor ReLEx Fs-Lasik Decentration (mm) from corneal apex ,2 0,2-05 0,5-1 >1 1 1

11 Discussion 1. The centration of the treatment zone as measured by Pentacam is in favour of patient controlled fixation during the ReLEx procedure compared to active eye-tracker assisted Femtolasik surgery. 2. Self-centration during ReLEx treatment shows a trend toward nasalisation of the treatment zone in relation to the pupil center (natural angle κ) and is closer to the corneal vertex. 3. Self-centration appears to work better in asian eyes* (mean 0.17 ± 0.09 mm; 100% within 0.50 mm ; 70% within 0.20 mm; and 90% were within 0.30 mm): Head tilt? *Li M. et al. Invest Ophthalmol Sci, May 2014 But does self-centration control cyclotorsion? And What is the degree of cyclotorsion?

12 Distribution of error and astigmatism Cyclotorsional Axis Error Astigmatism Assuming Normal distribution Mean cyclotorsion: 3.3 ± 2.4 Calculated from 9,887 eyes presenting for LASIK 0.25 D or more error in 11.8% of eyes 0.50 D or more error in 3.1% of eyes Courtesy of DZ Reinstein, London

13 Ways of cyclotorsion control The Danish method (Ivarsen et al, JRS 2014)

Study by Brar & Ganesh/India, 2016 Once centration achieved eye docked followed by application of suction With the suction on, the extent of cyclotorsion was determined using the reticule

14 Study by Brar & Ganesh/India, 2016 Once centration achieved eye docked followed by application of suction With the suction on, the extent of cyclotorsion was determined using the reticule in the right eye piece Any cylotorsion was measured in degrees by noting the relative position of the limbal marks in relation to the degree axis of the reticule/screen with protractor

15 PREOPERATIVE DATA Low cylinder ( 1.5D) High cylinder >1.5D NO OF EYES Mean SE(D) ± ± 2.27 Mean Cylinder(D) -1.09D ± D ± Mean Cyclotorsion (Deg) 3.46 (0-15) 2.36 (0-10) Study by Brar & Ganesh/India, 2016

16 3 months post operative Low cylinder ( -1.5D) High cylinder ( >-1.5D) Mean SE(D) ± ± 0.36 Mean Cylinder(D) ± ± 0.23 Study by Brar & Ganesh/India, 2016

17 Study by Brar & Ganesh/India, 2016 CORRECTION INDEX=sia/tia= MEASURE OF AMOUNT OF CORRECTION (IDEAL= 1) <1:UNDERCORRECTION, >1:OVERCORRECTION Low cylinder=0.91 High cylinder=0.92

18 Study by Brar & Ganesh/India, 2016 Index of success(ios)- RELATIVE MEASURE OF SUCCESS OF CORRECTION, SMALLER THE VALUE, BETTER IOS Low cylinder=0.16 High cylinder=0.06

19 Ways of cyclotorsion control My current routine approach: Reticule in the eye-piece is in the non-dominant eye This reticule is aligned with the screen reticule Watch the Purkinje image in the 1 st position (observation) Applanate up to 90%, but not too hard, watching for rotational movements Marks at 3-9 o clock position outside the laser area, if cyl> 1.5D Adjust the head in the observation position (prior to suction) Correct if necessary by twisting the suction cone ( contact glass ) If possible use larger zones ( mm)

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