Costas Karabatsas MD, PhD, MRCOphth, FEBOphth, FRCS Ophth Irregular Corneal Astigmatism & Cataract (assessing ocular surface, IOL selection)
In both LRS and Cataract Surgery aim = Emmetropia Refractive expectations of cataract surgery patients today are very high. Expecting emmetropia as if they had LRS performed Spherical emmetropia is relatively easily achieved after cataract extraction nowadays 2
Preop (subjective) astigmatism is a combination of corneal AND lenticular astigmatism Provided that our IOL is correctly positioned and not creating astigmatism Postop refractive astigmatism will depend upon the neutralization of corneal astigmatism with a combination of techniques In order to fully correct corneal astigmatism, this has to be properly evaluated first
Preoperative astigmatism evaluation Today we can improve our refractive cataract surgery outcomes by skillful interpretation of corneal mapping Placido Scheimplug Cassini 4
Placido systems 5
Oculyzer (Scheimpflug) 6
Cassini 7
Irregular Astigmatism definition has changed 8
Astigmatism definition 9
Astigmatism classification 10
11 PK astigmatism classification based on corneal topography Karabatsas CH et al : Proposed classification for topographic patterns seen after penetrating keratoplasty Br J Ophthalmol 1999; 83:403-9.
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Post-PK astigmatism 80 60 40 20 0 3 M. 6 M. 9 M. 12 M. Non astigmatic REGULAR IRREGULAR 13
RESULTS Oblate Asymmetric Bow-Tie (OABT) was the regular pattern more often found in keratoconic corneas.
Irregular Astigmatism management Before cataract surgery At the same time as cataract surgery After cataract surgery
Μethods of Astigmatism Correction 1) by changing Corneal Curvature Astigmatic keratotomies (straight / arcuate) Relaxing keratotomies near limbus ΡRΚ / LASIK Femto RKs 2) by refractive neutralization of existing Corneal Astigmatism Toric intraocular lenses 16
Astigmatism correction at the time of surgery implanting toric IOLs executing laser arcuate incisions the simplest and most cost-effective is the manual LRI
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Residual astigmatism correction with T-IOL 19
ΑSTIGMATIC KERATOTOMY (ΑΚ / LRIs) Used in : Naturally occurring astigmatism Postoperative astigmatism Post cataract surgery Post - PKP Post PRK KC Athens 2008 20
nomograms ASTIGMATIC KERATOTOMIES instruments corneal topography (placido) results 21
Cataract Onaxis Incision 22
2 3 Corneal Architecture Corneal behavior is similar to an elastic dome, which is placed over a round scaffold (limbus) with a diameter remaining always stable, despite any procedures to the surface of the dome
Βasic Principles of Astigmatic Keratotomy 1. The AK is always placed on the STEEP meridian [ (+) cyl axis ] 2. Transverse sections on the (+) axis result in FLATTENNING of this meridian, with concurrent steepening of the meridian at 90 ο 24
Refractive result of a Transverse Relaxing Incision INCREASE of R => FLATTENING of the cornea => Reduction of refractive power over this meridian 25
Βasic Principles of Astigmatic Keratotomy 3. The closer to the optic axis the transverse keratotomies (small ΟΖ), the greater effect 4. > 2 pairs of TK on the same meridian do not increase significantly the astigmatic result 5. Keratotomy depth < 80% 6. Max keratotomy length is 3 clock hours [90 ο ] (spheq ct) 26
Straight transverse T- cuts single symmetric pair multiple Arcuate transverse T symmetric pair asymmetric pair TRANSVERSE KERATOTOMIES but always transverse to (+) axis 27
What is an LRI? Partial-thickness penetrating incisions typically placed within 1 mm of the limbus and, as such, can more accurately be named peripheral corneal relaxing incisions. These incisions can effectively correct upwards of 1.25 to 1.50 D of corneal astigmatism. A preset depth of 600 µm can be used, as can a variable depth with pachymetry set at 90% of the thinnest pachymetry reading. well-established nomograms Koch/Wang, Nichamin Age Pachymetry Adjusted Intralimbal Astigmatic [NAPA] Donnenfeld www.lricalculator.com.
LRIs tips Manual limbal relaxing incisions (LRIs) and LRIs in general can produce a hyperopic shift of about 0.20 D, so it is sometimes advisable to choose a higher-powered IOL than is suggested by the IOL power calculation Any bleeding from corneal neovascularization can blunt the desired flattening effect of the LRI If an overcorrection occurs, it is safest to wait 2 to 3 months before performing any enhancements.
A slight undercorrection can instantaneously be adjusted by creating a new LRI central to the existing one or lengthening the existing LRI (Figure)
Manual LRIs Although manual LRIs can be less predictable than other options, they are a triedand-true strategy for correcting low levels of corneal astigmatism. Every cataract surgeon who is committed to maximizing refractive outcomes should be knowledgeable about and proficient at performing this particular type of corneal relaxing incision
LRIs advantages : LRIs are cost-effective. LRIs are an excellent means by which to fix low amounts of astigmatism (< 1.00 D) when a toric IOL is not available for the patient, they are also a less expensive option than a toric IOL. usually taking less than 5 minutes to perform. manual incisions are ergonomically friendlier for the surgeon and more comfortable for the patient than laser arcuate incisions. they can be performed on the spot, not the case with toric IOLs or laser arcuate incisions.
Why should you perform manual LRIs?
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video
Femto AK
Correction of residual astigmatism by refractive surgery PRK LASIK Topography-guided ablations 40
Topo-guided LASIK advantages Correction of irregular astigmatism Regular & smooth corneal surfaces can be obtained (improved BSCVA) Transition zone size can be topo-guided to maintain a constant minimum slope @ 360 o to avoid regression μm of ablation can be saved compared to standard ablation 41