Intraoperative fine tuning of sphere & cylinder

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Ilene Carpenter
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1 Intraoperative fine tuning of sphere & cylinder Hussein Ali Alex. University ESOIRS 2015 Intraoperative fine tuning of sphere 1

2 IOL power calculation r requirements - Axial length by IOL Master - Precise Keratometry - Prediction of ELP Prediction of ELP Accuracy of ELP Depends on : - IOL formula - Surgical technique to implant the IOL in the capsular bag at the plane of the zonules anterior displacement gives myopic shift posterior displacement gives hyperopic shift - Refine your lens constant your technique should be consistent 2

3 Variables affecting estimation of final IOL position (ELP ) - surgical variations in capsulorhexis - IOL thickness, material, haptics design Configuration of capsulorhexis CCC maintains a consistent ELP CCC should be round, central &smaller than IOL optic with circumferential capsular overlap of IOL optic - CCC larger than IOL optic : forces of capsular contraction displace the IOL Anteriorly - Small CCC can cause capsular Phimosis or capsular block syndrome & should be enlarged 3

4 Influence of IOL haptics design - The floppier haptics of 1-piece IOL have minimal early axial displacement but do not offer resistance to capsular contraction - there early forward IOL shift of 3-piece IOL after one month it may better resist capsular contraction & over perform the 1-piece IOL & provide more predictable ELP. ( Savini et al 2014 ) Diopteric changes in eyes with reversed IOLs the Diopteric change depends on IOL design: - Anterior biconvex IOLs with similar anterior & posterior radii : no change - Posterior biconvex IOLs have smaller posterior radius & results in myopic shift - Convex-plano IOLs results in hyperopic shift 4

5 IOLs placed in the sulcus IOL power should be decreased depending on IOL power when placed in the sulcus D D no change D 17.0 D 0.5 D D 27.0 D 1.0 D D 35.0 D 1.0 D Perfect centration of IOL IOL Decentration causes defocus,asigmatism,hoa & coma - Intraoperative cent ration of IOL optic on the visual axis is important especially in aspheric, Toric & multifocal IOLs - IOLs with zero spherical aberration have better visual outcome in IOL decentration 5

6 Perfect centration of IOL Causes of Decentration : - in out of the bag placement - big capsular bag - IOL in sulcus - radial bag tears - capsular Phimosis Causes of Decentraton : Asymmetric, eccentric or irregular CCC result in asymmetric capsular forces & delayed optic Decentration, tilt & shift in ELP If zonules are weak insert a CTR 6

7 Perfect centration of IOL Premium IOLs are contraindicated in : - super prolate cornea - decentered visual axis in Keratoconus - decentred corneal refractive surgery Correction of Astigmatism 7

8 . Astigmatism decreases visual acuity through meridional blur As little as 0.5 D may result in glare, ghosts, haloes & image blur Patients with PC-IOLs are sensitive to minor degrees of astigmatism Determining what to correct? Planning correction with cataract surgery is based on corneal astigmatism not on refractive astigmatism Planning correction and enhancement in Aphakic & pseudophakic eyes is based on refraction 8

9 Measurement of astigmatism Manual & auto-keratometer Corneal topography IOL Master. Corneal topography Confirm Keratometry measurements Detect cornea with risks of ectasia. Keratoconus Marginal corneal disease Detect asymmetric cornea 9

10 Preoperative measurements Readings from different devices do not always correlate & there is disagreement in axis location between these devices especially with low astigmatism Astigmatic power & axis is best determined by a combined assessment of 2 or 3 devices Preoperative steep axis determination Inaccurate measurement of steep axis may result in under correction of astigmatism Axis deviation of 5,10,15 degrees will result in 17%,33% or 50% reduction in effect 10

11 Pre operative markings Once the patient is draped, it can be hard to identify the horizontal meridian. Eye rotation may occur in supine position : - Cyclotortion - Change of patient position on operating table or head tilt. Preoperative markings Keratometry is recorded with the patient upright whereas ocular surgery is performed with the patient supine Cyclotortion may occur when the patient assumes a supine position. 11

12 Preoperative marking of the eye 2 steps: o clock meridians A marking pen covers 10 degrees at the limbus Use an insulin syringe for marking Steep Axis marking: Axis of IOL orientation. 12

13 Strategies for minimizing preoperative astigmatism Phaco incision on steep axis ( 0.5D) Paired CCIs on steep axis (1-1.5 D). PCRIs ( 1-2 D ) Toric IOL (1-4 D) Used alone or in combination. On axis incision Today cataract incisions are small & induce small amount of astigmatism - A 3.2mm CCI results in SIA of D - Making the incision less than 2.4 mm wide does not reduce SIA much because incisions stretch during IOL implantation.( Hill 2008 ). 13

14 On axis incision vs Temporal incision Many surgeons prefer operating temporally on all eyes Giang 2006 did not find significant difference between SIA induced by temporal & on axis CCI, Opposite clear corneal incision The same keratome can be used to make an opposite CCI. It corrects D of astigmatism Results are variable & regression may occur. 14

15 The surgically induced astigmatism - No incision is astigmatic ally neutral. The cataract incision changes the vector of preoperative astigmatism. -The two are added together to create the post operative astigmatism. - The new astigmatism has a new power & axis.. A big mistake is to place a Toric IOL or PCRI at Keratometric or topographic axis & do not consider SIA. 15

16 The surgically induced astigmatism calculator Surgeon downloads the SIA calculator Enter incision location, steep K, flat K, flat meridian & postoperative steep & flat K After 10 cases, he can obtain the magnitude of his SIA. Determining surgically induced astigmatism For use with on-line toric IOL calculator Surgically Induced Astigmatism Calculator SIAC.xls Free, downloadable stand-alone Microsoft Excel program. Warren E. Hill, MD, FACS 16

17 . Astigmatism effect of major cataract incision ( SIA ) : CCI 3mm 0.5 D SIA Corneal incision > limbal > scleral Superior CCI > temporal. Coaxial > biaxial. Peripheral Corneal Relaxing Incisions PCRIs are successful in Correcting moderate astigmatism beyond 2 D astigmatism risks overweight benefits 17

18 Contraindications to PCRIs Keratoconus. Peripheral corneal pathology. Prior RK. Severe dry eye. Autoimmune disease PCRIs The results of PCRIs are variable & depend on - incision length & depth - size of optical zone relative to corneal diameter - patient age - type of astigmatism 18

19 PCRIs Nomograms J. Gills D.Koch R.Lindsrom B.Wallace L.Nichamin E.Donnenfeld Improved nomograms NAPA (Nichamine age & pachymetry adjusted) nomograms based on patient s age angular nomograms Pachymetry adjusted nomograms 19

20 Improved nomograms Consider astigmatic effect of major cataract incision www LRIcalculator.com uses vector analysis to calculate where to make LRIs based on preoperative Keratometry & surgeon induced astigmatism Creates a surgical diagram & plan of location & length of LRIs that can be copied & brought to operating room. 20

21 Surgical procedure pachymetric reading Over the entire arc length of intended incision To achieve predictable permanent results incision must be 90% of corneal thickness Surgical procedure Center the guide instrument on the cornea Knife perpendicular. 0.5 mm inside limbus. Press firmly to full depth. Extend incision from mark to mark. 21

22 Toric IOLs Proper selection of patients Regular corneal astigmatism ( 1 D 4 D ) Intact capsule and zonules Central round CCC ( 5 mm ) In the bag fixation Cyl Powers, SN6AT2-T5 *Based on an average human eye AcrySof Toric IOL Model Cylinder Power of IOL Cylinder Corneal Plane* SN6AT SN6AT SN6AT SN60T

23 Cyl Powers, soon, SN6AT6-T9 *Based on an average human eye AcrySof Toric IOL Model Cylinder Power of IOL Approx cylinder Corneal Plane* SN6AT SN6AT SN6AT SN6AT Determine the vector sum of preoperative corneal astigmatism & SIA before selecting the IOL Online Toric power calculators are available 23

24 AcrySof IQ Toric IOL Calculator Makes precise surgical planning easy! Intuitive input Patient data Keratometry IOL spherical power Surgically induced astigmatism Incision location Powerful output Recommended IOL model and spherical equivalent power Optimal axis placement Magnitude and axis of anticipated residual astigmatism Final dialing & axis alignment 24

25 Toric IOL Pros: Excellent predictability. No induced irregular astigmatism. Rapid visual rehabilitation. Cons: High cost. Less effective in correcting asymmetrical bowtie. Correcting corneal astigmatism with lens at IOL planeproduces distortion. LRIs Vs Toric IOL LRIs Pros: Easy - safe. Patient will not pay. Incisions do not rotate. Can be enhanced postoperatively Can enhance Toric IOLs Works well for asymmetric cornea. 25

26 LRIs Vs Toric IOL LRIs Cons: Less predictable in high astigmatism Less effective in young age. FB sensation. Not suitable in dry eye rheumatoid disease, post RK. 26

Incision along Steep Axis

Toric IOL An option or a must? ~ 15% cataract surgical patients >1.5 D Options: spectacles, CLs, Incision along steep axis, LRI, AK, toric IOL, Excimer Laser or a combination Walter J. Stark, MD Professor