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INCISIONAL CORNEAL SURGERY ( AK , LRIs )

INCISIONAL CORNEAL SURGERY ( AK , LRIs ). M . NOURI FESHARAKI MD.  In modern phaco surgeons no longer seek to avoid inducing ast. but rather must address to reduce significant pre-existing cylinder.

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INCISIONAL CORNEAL SURGERY ( AK , LRIs )

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  1. INCISIONAL CORNEAL SURGERY ( AK , LRIs ) M . NOURI FESHARAKI MD

  2. In modern phaco surgeons no longer seek to avoid inducing ast. but rather must address to reduce significant pre-existing cylinder. Patients have now come to judge the success of their surgery largely by their refractive result.

  3. Several different methods may be employed to achieve this goal . 1- Placing the incision upon the steep meridian 2- Varying size and design of incision . 3- Relaxing incisions . 4- Toric intraocular lens . 5- Bioptics approach (excimer laser or other keratorefractive modality).

  4. In conjunction with cataract surgery Incisional procedures can be used to reduce or eliminate astigmatism.( > 0.75 D ) The most common incisional surgery for the correction of astigmatism associated with cataract surgery is the limbal relaxing incisions (LRIs). LRIs for the correction of mixed ast. can be very safe , inexpensive , useful technique for surgeons experienced in incisional surgical techniques.

  5. Arcute incisions and transverse incisions are both placed in the steep meridian of the cornea. Both techniques flatten the steep meridian of the cornea and cause steepening of the opposite meridian (coupling). Although the coupling ratio can be quite variable,in general the meridian of the incision will flatten approximately 2 to 3 times as much as the opposite meridian will steepen.

  6. Pre - op Evaluation • Topography –keratometry to detect steep meridian • Evaluation of tear film (no incisional keratotomy in moderate to sever dry eye • Evaluation of fellow eye • R/0 keratoconus

  7. Arcuate Keratotomy • %95 depth in 7 mm optical zone • Depend to age –length – number of incision • 2/3 effect with first symmetric incision • Lesser effect in young patient ( < 30 y decreased 0.2 D/year • Coupling effect .

  8. 30 -90 degree AK CR =1 stable SE no change IOL power . AK<20 CR >1 hyperopic shift AK>90 CR < 1 myopic shift.

  9. At study in eyes undergoing phaco , evaluated the efficacy of paired intraoperative arcuate keratotomy combine with 3.5 mm limbal steep axis clear corneal incision. Arcute incisions were performed in the steep axis at 7 mm optical zone based on lindstrom nomogram ( after 8 weeks). Arcute group 2.281.02 D (1.26 D) S Arcute group 2.041.55 D (0.48 D)

  10. Limbal Relaxing Incisions The notion of Astigmatic relaxing incisions in cataract procedures : Osher mid .1980. For many years corneal incisions done at 7 mm optical zone . Although effective , causes irregular ast.  More recently , a number of authors have recommended moving these incisions out to the peripheral cornea .Indeed these LRI are proving to be a less demanding and more forgiving approach to Ast.

  11. LRIs advantages -Less likely to cause a shift in the resultant cylinder axis (deminished need to centration). - Technically , they are easier to perform . - Patients generally report less discomfort. - Coupling ratio ,(1:1 ratio) negligible change in spheroequivalent (no need to adjust the IOL power) - Peripheral incisions are less powerful but are still capable of correcting up to 3-4 diopters.  For these reasons more refractive surgeons now prefer LRIs for all patients.

  12. Incision Strategy Because of decrease incision sizes under 3.5 mm in single plane or beveled fashion causes astigmatically neutral incision. Most authors would agree that mild residual with-the-rule ast. is desirable since most patients will drift against-the-rule over their lifetime, and such residual ast. may enlarge the conoid of sturm , increasing the depth of focus. Keratometry tends to provide an accurate determination of Ast. axis , topography also can be helpful.

  13. LRIs Surgical technique - At the onset of surgery . - One exception (against-the-rule Ast.) - Most surgeons placing an orientation mark at 6 or 12 o clock limbus in an upright position . - Furthermore , it is helpful to identify the steep maridian intraoperatively by using keratoscopy. - The LRIs are placed at the most peripheral extent of clear corneal tissue , just inside the true surgical limbus irrespective of the pannus - Empiric blade depth setting :600 µm.

  14. Trapezoid shape blade • Back –cutting better in LRIs • Front – cutting better in AK

  15. Post – PkArcuate Keratotomy AK in graft –host interface or in graft 45 - 90 degree , > 6 mm o . Z Evaluation by lindstromnomogram and keratoscopy In high astig , Have high response Pre –op 10 D astigmatism decreased to 3 .3 post –op Misallignment 15 degree % 50 decreased effect 15-30 degree shift of axis and no effec > 30 degree increased astig

  16. Complications Infection - Weakening of the globe - Perforation (BCL –Suture ) - Decrease corneal sensation – Dry eye - Induced irregular astigmatism - Misalignment/ axis shift - Glare - Wound gape and discomfort(in long –horizontal ) Central – corneal epitheliopathy (more in horizontal meridian )

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