Toric iol

Brief and salient points about Toric intraocular lenses

1. TORIC IOL’s Jagdish Dukre

2. Modern cataract surgery is more of refractive surgery. Myopia & hypermetropia can be corrected using appropriate spherical powers of IOL’s. However approximately 20% of patients who undergo cataract surgery have 1.25D of corneal astigmatism or more. It can be corrected with Toric IOL’s.

3. Other options for correction of co-existent cataract and astigmatism LRI during cataract surgery( upredictable results) Laser procedures postoperatively (are associated with new set of complications).

4. History of Toric IOL’s First introduced by Shimizu et al in 1994. It was nonfoldable 3 piece toric IOL made from PMMA. It had oval optic with loop haptics ,available in cylinder power 2-3 D. Postoperatively 20% IOL’s rotated > 30 degrees and 50% IOL rotated about 10 degrees.

5. AVAILABLE TORIC IOLs

6. Model of Acrysof IQ Toric Model Cylinder power at IOL plane(D) Cylinder Power at corneal plane(D) SN60AT3 1.50 1.03 SN60AT4 2.25 1.55 SN60AT5 3.00 2.06 SN60AT6 3.75 2.57 SN60AT7 4.50 3.08 SN60AT8 5.25 3.60 SN60AT9 6.00 4.11 Spherical powers available are 16- 25 D.

7. Factor Affecting Rotation of Toric IOL IOL material Hydrophobic Acrylic < Hydrophilic Acrylic < PMMA < Silicon (2) Overall IOL diameter - Larger diameter prevents rotation . Toric IOL’s are available nowadays in 11-13 mm overall diameter. (3) Haptic design – Initial concept - Loop haptics prevent early rotation . - Plate haptics prevent late rotation. Recent concept – No difference in incidence of post operative rotation between plate and loop haptics provided material of both loop and plate is same.

8. Patient selection Regular corneal astigmatism > 1.5 D Vision compromising cataract Patient wants spectacle independence

9. Facts 20% of patients with cataract have astigmatism >1.25 D Every incision on cornea induces additonal astigmatism (SIA). Implantation of monofocal lens will require distance and near correction both in these cases. B/L Toric IOL’s give high level of spectacle independence(97%). Requirement of near correction can be overcome by multifocal toric IOL( AcriLisa multifocal toric IOL)

10. Toric IOL power calculation : Precise keratometry Surgically induced astgmatism [SIA].

11. Keratometry Can be done with Manual keratometer Automated keratometer with steps of 0.12 only Corneal topography K readings from all the three show high repeatability and are comparable. Manual keratometer should be calibrated regularly.

12. Corneal topography is required in case of unusual reading & poor quality mires. Precautions Reading must be quick to avoid drying of cornea. Don’t rub on the cornea. Centration must be proper.

13. Surgically Induced Astigmatism Every incision changes the cornea. Closer to the centre & larger the incision more effect on corneal curvature. Other factors affecting it are preoprative corneal astigmatism, suture use and patient’s age. In addition there is variability from patient to patient. Overall effect can be summed up with vector analysis.

14. SIA Calculation Obtain SIA calculator Fill it for 20-30 cases minimum Be precise about axis and incision Calculator auto calculates SIA

15. AcrySof Toric IOL Calculator Data input Patient data Keratometry IOL spherical power Surgically induced astigmatism Incision location 15

16. Output screen Recommended IOL model and spherical equivalent power Optimal axis placement Magnitude and axis of anticipated residual astigmatism 16

17. Marking of Eye Instruments Bubble marker Gravity marker

18. STEPS A) Reference marking Done prior to surgery with patient upright Two reference markers placed at limbus 180 degree apart Used to align marking instuments for placement of axis marks B) Axis marking : Using reference marks as a guide the patient eye is marked accurately at two positions 180 degree apart TIPS:- - Dry the conjunctiva with a swab - Enhance marking at 3-9 o clock - Apply mark with twisting action - It lasts throughout surgery

19. Surgery Standard phacoemulsification Incision size 1.5 – 3.4 mm Well centered rhexis with diameter 5- 5.5 mm with 360 degrees overlap of IOL margin Marks on IOL indicate flat meridian or plus cylinder axis of toric IOL Cohesive viscoelastics are preferred.

20. IOL alignment Tap (“nudge”) IOL down into capsular bag to seat lens onto the posterior capsule.

21. If any compromise of zonular integrity or capsule occurs please switch to standard non toric IOL Postoperative axis alignment : Slit Lamp with dilated pupil Wavefront aberrometry in undilated pupil Realignment should be done in < 2 wks

22. Complications Rotational stability is critical to effectiveness of toric IOLs. 1° rotation results in 3.3 % IOL power loss 30° rotation negates cylindrical correction of toric IOL Further rotation induces more astigmatism 22

23. Conclusion Bilateral toric IOL implantation shows high percentage of spectacle independence for distance vision.