1. Astigmatism correction methods
Alireza Peyman, MD

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 Incisional methods
Soft (toric)
RGP
orthokeratology
Incisional methods
Traditional
FS assisted
full thickness paired incisions
Intra-corneal inlays
Excimer ablation
Toric pIOLs
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 LRI Induced wound dehiscence
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 R/O KC
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
Belin enhaced ectasia 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
Toric Artiflex
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 داخلی 392 تماس حاصل نمائید با تشکر