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.

Patients have now come to judge the

success of their surgery largely by their

refractive result.

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).

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.

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.

Pre - op EvaluationTopography –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

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 .

30 -90 degree AK CR =1 stable SE

no change IOL power .

AK<20 CR >1 hyperopic shift

AK>90 CR < 1 myopic shift.

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 2.28 1.02 D (1.26 D) S Arcute group 2.04 1.55 D (0.48 D)

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.

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.

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.

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.

Trapezoid shape blade

Back –cutting better in LRIs

Front – cutting better in AK

Post – Pk Arcuate KeratotomyAK in graft –host interface or in graft 45 - 90 degree , > 6 mm o . ZEvaluation by lindstrom nomogram and keratoscopyIn high astig , Have high responsePre –op 10 D astigmatism decreased to 3 .3 post –opMisallignment 15 degree % 50 decreased effect 15-30 degree shift of axis and no effec > 30 degree increased astig

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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