Astigmatism correction methods Alireza Peyman, MD

1. Astigmatism correction methods Alireza Peyman, MD http://www.drpeyman.ir

2. One of the troublesome aspects of refractive surgery

3. What is astigmatism • Regular • Irregular

4. Regular astigmatism

5. Presbyopic with the rule in near vision

6. Source of astigmatism • Cornea-tear film • Crystalline lens • Including tilt • Posterior segment

7. Measurement of astigmatism • Auto-refraction and retinoscopy • Subjective refraction • Astigmatic dial • Cross cylinder • Wavefront PPR • Keratometry • Automated or manual • ORA could be calculated

8. Correction methods • Glasses • Contacts • Soft (toric) • RGP • orthokeratology • Incisional methods • Traditional • FS assisted • full thickness paired incisions • Intra-corneal inlays • Excimer ablation • ToricpIOLs • Toric IOLs

9. Glasses • Easy and difficult! • Cause distortion of images and depth due to dissimilar meridional magnification in eyes

10. Easy cases • Persons that have had astigmatic glasses for years or from childhood • Minor vertical or horizontal astigmats • Monocular patients, and children

11. Most difficult ones • New glasses with > 2.5 diopters of oblique astigmatism and enantiomorphism • Impaired proprioception (diabetics in some stages)

12. Contact lens • Always worth try in difficult cases • Irreplaceable for irregular astigmatism

13. Incisional methods • AK • Arcuate • Straight • LRI • Induced wound dehiscence • After PKP or improperly sutured wounds • Compression sutures & wedge resection • Paired full 3.2 incision • FS assisted

14. Incisional methods mostly used during or after a major intra-ocular surgery like cataract extraction or PKP

15. Corneal inlays • ICRS • Intra-corneal lenses

16. Excimer ablation • Case selection • R/O lens problems • Lens tilt or subluxation • Lenticonus • R/O KC

17. Evaluations • Inquiry about recent refractive change and FHx of KC are important • Check both Placido based topographies and elevations • In Pentacam check • 4 map • Front & Back elevations in detail • Belinenhacedectasia map • Refractive map for KC indices

20. Toric ellipsoid fixed reference body

23. Use front and back Pentacam elevation maps with “toric ellipsoid fixed” reference if you have decided to proceed to surgery.

24. Measurements • Always look at autorefraction • Check subjective refraction and BCVA • Consider keratometric astigmatism • Amount • Axis • Check PPR and optical aberrations

25. Decide for the amount and axis of the correction seeing all measurements • Under-correct the power for at least 5% to decrease induced astigmatism due to angle of error of corrections. • Check, check, and recheck the numbers at each stage.

26. Determine ablation protocol • Conventional (Plano-scan) • Tissue Saving • Aspheric • Customized WF guided

27. WF guided ablation(APT) • Best for moderately aberrated corneas • Not suitable for highly aberrated eyes • Removes much higher amount of tissue • Post-op hyperopia may arise • Not appropriate for patients with non-corneal aberrations • Crystalline lens opacities • Cloudiness of vitreous • No benefit in eyes with low aberration

28. Errors of angle of correction • Exact alignment of measured angle of astigmatism with angle of correction is of paramount importance for best results in astigmatic correction.

29. Basis of error in angle alignment • Position of head and eyes are different in upright measurement phase and supine correction stage. • Incorrect position of head compared to body in operation cradle. • Misaligned and unlucked operating bed.

33. Only 5 degrees of tilt make difference

35. Head tilt in upright position

36. This type of rotation does not occur in supine position. • This phenomenon cause error even if the amount of tilt were similar in upright and supine positions

37. Rotational registration • Manual • Mark 90, 180, and 270 in upright • Re-align with axes in operating bed • Automated • Iris image registration

38. Automated Iris registration • Takes iris image in sitting position • Takes another image immediately before Sx and compensate rotation comparing two images

39. Iris registration tips • Add another image taken in exam room with room lights on • Turn off lights in OR • Align with pupil center exactly • Don’t move head until beginning of ablation

40. Tips (cont.) • If registration unsuccessful: • Turn off all lights even of monitor and red green target lights • Use both of two LED IR light sources • I prefer to remove epithelium before registration for quick continuing of the surgery.

41. Toric pIOLs & IOLs • Available options: • Toric phakic artisan • ToricArtiflex • Toric ICL • Toric IOLs of multiple brands • Toric supplement IOLs for sulcus

42. Drawbacks • Cost • Availability • Imaginable complications with intra-ocular surgery • Problems with stability of lens

43. Occasionally Difficult pre-op marking • Sometimes difficult intra-operative alignment

44. ضمن عرض پوزش بدلیل حجم بالای LECTUER ادامه اسلایدها امکان پذیر نمیباشد در صورت نیاز به ادامه لطفا به واحد سمعی و بصری مرکز آموزشی درمانی فیض مراجعه و یا با شماره تلفن 03114476010 داخلی 392تماس حاصل نمائید با تشکر