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
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.freiheitlich.me www.sueddeutsche.de Excimer laser: I am in charge using sophisticated machinery VisuMax fs-laser: I, the surgeon, have to (partially) rely on the patient
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 36 37 (22 to 55) 34 35 16 20 51-5.96 (-1.25 to -10) -0.95 (0 to -4.0) 43.53 fs-lasik 36 34 (23 to 65) 33 36 16 20 63-4.96 (-0.75 to -10) -1 (0 to -4.5) 43.43 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 -5.76 (-1.25 to -10) -0.79 (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 -4.88 (-0.75 to -10) -0.91 (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 -4.75 Dpt Decentration from Apex: 0.297mm Decentration from Pupil centre: 0.180 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 - 5.38 Dpt Decentration from Apex: 0.533 mm Decentration from Pupil Centre: 0.421 Thickest point Fs-LASIK (OS) Mean Spherical Equivalent of the Correction - 5.38 Dpt Decentration from Apex: 0.149 mm Decentration from Pupil Centre : 0.041 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: 0.243 Thickest point ReLEx Smile (OS) Mean Spherical Equivalent of the Correction - 8.25 Dpt Decentration from Apex: 0.863 mm Decentration from Pupil Centre: 1.062 Thickest point
Results Decentration in relation to the corneal apex (0,0) 1.50 OD, OS 1.50 OD, OS 1.00 1.00 0.50 0.50 0.00-1.50-1.00-0.50 0.00 0.50 1.00 1.50 0.00-1.50-1.00-0.50 0.00 0.50 1.00 1.50-0.50-0.50-1.00-1.00-1.50-1.50 ReLEx Mean Decentration: 0.315 fs-lasik Mean Decentration: 0.516
Results Decentration in relation to the pupil centre (0,0) 1.50 OD, OS 1.50 OD, OS 1.00 1.00 0.50 0.50 0.00-1.50-1.00-0.50 0.00 0.50 1.00 1.50 0.00-1.50-1.00-0.50 0.00 0.50 1.00 1.50-0.50-0.50-1.00-1.00-1.50-1.50 ReLEx Nasalisation of the fixation in relation to the pupil centre = positive angle κ Mean Decentration: 0.326 fs-lasik Centration is randomly distributed Mean Decentration: 0.452
Results: Summary 45 40 35 30 25 20 15 10 5 0 Decentration (mm) from pupil centre 42 35 23 16 9 10 1 2 0-0,2 0,2-05 0,5-1 >1 perfect good acceptable poor 35 30 25 20 24 ReLEx Fs-Lasik Decentration (mm) from corneal apex 32 28 31 15 10 9 12 5 0 0-0,2 0,2-05 0,5-1 >1 1 1
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?
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
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 in the right eye piece Any cylotorsion was measured in degrees by noting the relative position of the limbal marks in relation to the 0-180 degree axis of the reticule/screen with protractor
PREOPERATIVE DATA Low cylinder ( 1.5D) High cylinder >1.5D NO OF EYES 71 72 Mean SE(D) -5.01 ± 2.45-5.14 ± 2.27 Mean Cylinder(D) -1.09D ± 0.509-2.46 D ± 0.705 Mean Cyclotorsion (Deg) 3.46 (0-15) 2.36 (0-10) Study by Brar & Ganesh/India, 2016
3 months post operative Low cylinder ( -1.5D) High cylinder ( >-1.5D) Mean SE(D) -0.24 ± 0.35-0.37 ± 0.36 Mean Cylinder(D) -0.20 ± 0.40-0.25 ± 0.23 Study by Brar & Ganesh/India, 2016
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
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
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 (6.5-6.8mm)