EyeMail Insights
A look at limbal-relaxing incisions

As biometry and IOL technology have moved us toward refractive cataract surgery, incisional refractive surgery has reemerged as a much-needed tool to fine tune our endpoint.
The following thread—generated in response to a member’s request for guidance with astigmatic incisional correction—should help cataract surgeons feel comfortable making corneal relaxing incisions. Each technique discussed below is effective and reflects a tremendous amount of wisdom and experience. Choose one that makes you comfortable and begin creating a new level of post-op vision correction.
Keep in mind that any nomogram mentioned will provide results. As well, you will generate some slight differences that will create In effect your personal nomogram. Keep your astigmatic incisions peripheral incisions, at least peripheral to the 8-mm optical zone. Either measure with pachymetry and set your knife right on your reading or stick with the 600-mm incision in patients younger than 70 years old and 550 mm in patients older than 70. Take it slow and stop if a perforation occurs.
If you create a small perforation and stop, it is no more than a vertical side port incision. At most, it will take a simple suture to close.
Thank you to the experienced surgeons who participated in this discussion. This type of online conversation ensures ASCRS EyeMail is a valuable, instantly available resource. Nothing beats having 10 experienced colleagues electronically offering support when you embark on a journey into new territory. I know that any of those mentioned would be glad to give you personal coaching. Do not be afraid to e-mail them and ask for clarification. Incisional surgery for refining your post-op results can be gratifying to you and your patients.

I would like to begin to perform surgical astigmatism control using limbal relaxing incisions (LRIs) as part of my cataract surgeries. As a novice in this arena, I welcome comments on the following points:
1. Arcuate vs. T cuts
2. Blade type
3. Is optical zone important (6, 7, or 8 mm), or should one plunge into the cornea somewhere near the limbus?
4. Which nomogram should I begin with until I develop my own?
5. Are most of you doing the LRI at the beginning or end of cataract surgery?
6. Is special equipment necessary—other than a pachymeter, markers (please indicate type), and diamond blade (please indicate type)?
Michael Loeffler, M.D.
Lighthouse Point, Fla.

“Arcuate cuts give a much more regular topography than T cuts. T cuts also have a radial component that can affect the spherical equivalent and result in a hyperopic shift, whereas arcuate cuts have 1:1 coupling and should not affect the spherical equivalent. Regarding blades, in my experience, a rectangular trifacet diamond has worked well.
I have found that an 8-mm optical zone provides the best trade-off among surgical effect, minimizing incision length and providing regular topography. Optical zones of 7 mm provide even more powerful correction of cylinder, but at the expense of regular topography and should be used with caution. Optical zones less than 7 mm confer a high risk of irregular astigmatism and should not be used. 
True LRIs are much more forgiving but require a substantially greater total chord length of incised tissue to achieve a given effect. In my hands an 8-mm optical zone represents the ‘sweet spot.’
Dr. Charles Casebeer’s (M.D.) nomogram from the old radial keratotomy (RK) days was designed for a 7-mm optical zone but would be a reasonable place to start using an 8-mm optical zone.
I do a lot of single, 30-degree arcs, which don’t appear on this nomogram; in cases of with-the rule (WTR) astigmatism in recent years, I have tended to do these at the steeper hemi-meridian.
Dr. Casebeer recommended setting depth at 100% of minimum pachymetry plus 50 microns, which is added to overcome tissue compression that occurs with the rectangular trifacet diamond.
Many years ago I abandoned pachymetry for arcs placed at the time of cataract surgery in favor of recommendations by James P. Gills, (M.D., professor of ophthalmology, The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore), to use 600 microns for patients younger than 80 and 550 microns for those older than 80.
After routinely placing arcs for about the last 12 years in virtually all cataract patients with corneal cylinder of approximately 1 D or more there have been less than five micro-perforations and two macro-perforations requiring sutures. I still see many of the patients who had surgery a decade or more ago. I have seen no late post-op problems from these arcs and have been impressed with the long-term stability of the procedure.
I create LRIs at the beginning of surgery before entering the eye for paracentesis. After making arcs I fashion a Langerman groove temporally. I wish to belatedly acknowledge Dr. David W. Langerman’s (M.D.) great contribution of his hinged wound, which maximizes wound integrity for a given wound aspect ratio.
I abandoned markers approximately six years ago but strongly encourage their use while gaining experience. I still use my Chiron Arc-T knives (Chiron Corp., Emeryville, Calif.), which haven’t been available for years. We just replace the diamonds when necessary because we have not found a replacement handle that is as good or better.
Joel K. Shugar, M.D.
Perry, Fla.

For those of us who do not have optical zone markers, in an average cornea how far from the limbal vessels is an 8-mm optical zone?
Paula A. Hicks, M.D.
Yankton, S.D.

An 8-mm optical zone is approximately 1.5mm to 2.5 mm from the limbal vessels, depending on the white-to-white (WTW). I strongly recommend using arcuate markers set at an 8-mm optical zone when starting with this technique.
Dr. Shugar

I have been very satisfied with my LRI technique for many years. For patients younger than 80 years, I make a 600-micron incision; for those 80 years and older, I make a 500-micron incision. I make an arcuate incision as close to the limbus as possible in the steepest axis. My nomogram is as follows:
1.00-1.75 D cylinder, one 6-mm arc
2.00-2.75 D cylinder, two 6-mm arcs (180 degrees apart)
3.00-3.75 D cylinder, two 8-mm arcs
I set my caliper at 6 mm or 8 mm, depending on what I am trying to achieve. Then I straddle the actual axis marking at the limbus and make my arc between these two marks.
If topography shows a bow-tie type of astigmatism that is equal on both sides (and I am making only one incision), I pick the side farthest from my corneal cataract section. If the astigmatism is more on one side than the other, then I make it where the astigmatism is greater.
If the astigmatism is 2-2.75 D but primarily on one side, I usually make only one 8-mm incision on that side rather than the two 6-mm incisions.
The LRI is always done before any other incision for cataract surgery.
For a long time I moved my corneal section superiorly in cases in which the steepest astigmatism is temporal. However, for the past two years I have stopped doing that. Now I make my corneal section through the LRI incision. If you do this, be certain to place the corneal section blade (I use a diamond blade) flat in the bed and try to extend the incision as centrally as possible before entering the eye. That gives a good hinge effect for closure without the need for a suture. If a suture is needed, I remove it at one week.
Lawrence M. Loewenthal, M.D.
Sterling Heights, Mich.

I have always made my LRIs in terms of degrees of arc. To measure chord length, as you describe, gives more degrees with a smaller cornea, but for a typical eye have you found arc length differences are not meaningful?
Your technique is exciting because I would think it is far simpler than fiddling with degree markers to determine the length of the arc (continuing use of degree marker, of course, to determine the location of the center of the arc). Is your chord length measurement technique common?
If one really wanted to be precise, you could measure WTW and do the geometry to determine the correct chord length for each patient given the WTW and degrees desired.
Mitchell V. Gossman, M.D.
Saint Cloud, Minn.

“I have done this for several years. I recently reviewed 100 consecutive patients with a follow-up of at least three months and found that cylinder reduction was excellent, with final cylinder no more than 0.25-0.50 D at most. I have not done a review at one year or more (which I will do).
The technique is simple and has been effective in my hands as well as my partner’s hands. I have not had to make any adjustments for different corneal sizes, although that should be examined, theoretically.
Dr. Loewenthal

I use nomograms by Louis D. “Skip” Nichamin, M.D., for LRIs, to which I added LRI-C at the higher end of corrections.
Basically, with LRI-C the LRI is broken into three overlapping segments, with the middle segment approximately 0.5 mm more central than the outer segments. The C procedure, originally described by Dr. Canrobert Olivera (M.D.) of Brazil, was done at the 7 mm to 8 mm optical zones. I modified it for LRI, just inside the limbus in clear cornea.
For patients 60 years old and younger I use a pachymetry-adjusted nomogram. I perform the pachymetry measurements just before prepping the patient and take three measurements along each LRI site. I use the thinnest of the set of three measurements for each LRI site and set the blade depth to 90% of that.
Therefore, the two LRI depths may differ.
I use the pachymetry-adjusted nomogram in younger patients because they tend to have more aggressive healing and regression of LRIs. It’s important to mark the limbus at 12:00 and 6:00 with patients upright, just before they recline, because the eye can undergo spontaneous cyclotorsion when they are horizontal.
I then use a circular-degree gauge with lines at every 10 degrees and a two-wing modified RK marker to mark the extent or limits of the LRIs.
I use the Thornton Arcuate Diamond micrometer knife from Mastel Precision (Rapid City, S.D.). It is easier to do the LRIs at the beginning of the procedure. If the LRI is in the same location as my temporal clear corneal incision, I use the LRI as a groove for the incision but wait until the end of the case to extend the LRI to its full length. This prevents excessive corneal striae and LRI gaping during phacoemulsification.”
Jack A. Singer, M.D.
Randolph, Vt.

“You can use any trapezoidal or pointed blade [which allows preset] depth. Many of us have been using old RK keratomes!
Although I once measured pachymetry and aimed for 90%, I now set the diamond at 550 to 600 microns and place the incision as far peripherally as possible without getting into the arcade vessels. Given the degree of long-term problems I have seen with more central T cuts, I always try to make it an arcuate incision as far as possible from the corneal center.
It is far easier to do these before entering the anterior chamber if you are combining them with lensectomy surgery. After surgery, they can be performed at the slitlamp, but don’t expect the refraction and Ks to correlate well with the improvement in uncorrected visual acuity.
A number of nomograms is available, but I honestly believe the technique is imprecise enough that you would do better developing your own based on your particular surgeon factors. A general guide is that in the absence of any radial incisions, a 45-degree pair will reduce 1D of cylinder. (It should go without saying that you need to re-confirm that you are centering on the steep axis.) In eyes that have had RK, reduce the length by 50% to achieve the same effect.
Others may disagree, but I don’t believe anybody can dependably achieve more than 2D of correction, although this can occasionally be the case. I never make an incision more than 90 degrees of arc length—and rarely do even that.
I find the excimer laser to be a superior way to deal with post-operative cylinder.
J. Trevor Woodhams, M.D., F.A.A.O.
Atlanta

If you are performing arcuate cuts, which knife do you prefer? Because you like peripheral locations, do you also adjust where you place your cataract incision? For instance, if you have a temporal LRI to correct WTR astigmatism, do you still use the temporal location for your cataract wound? Do you use your old RK markers to outline a 45-degree segment or another measuring device? At which level of astigmatism are you starting?
I don’t perform corneal refractive surgery, so I would need to send out patients with severe astigmatism or residual refractive errors (assuming I don’t want to do piggyback or IOL exchange).
Dr. Loeffler

“I have developed a nomogram that has worked well. I use the markers from ASICO LLC (Westmont, Ill.) with my name on them. (I have no financial interest in them.) One marks in degrees and the other in millimeters. A new one (for marking in degrees) was available at the ASCRS•ASOA Symposium & Congress.
I use the 600-micron LRI knife from Acutome (Malvern, Pa.), which is inexpensive but effective.
Douglas D. Koch, M.D.
Houston

“I can usually count on 0.5-1 D of cylinder just from the limbal cataract entry itself, so I try to place this where it will do the most good on preexisting cylinder. A pearl: Go by the keratometry, not necessarily the refraction.
I have several knives that I prefer, but the 600-micron LRI that Dr. Koch mentions is fine.
I try to use the cataract incision itself as much as possible for its refractive effect. You can perform your LRIs first and then enter the ACD at the bottom of one if that is a convenient location. You don’t want to put an LRI at 90 degrees to your wound, though; it just counteracts the relaxing effect. Or you can make your primary entry site the usual 3 mm and then put your LRI on the opposite side.
Others may disagree, but I don’t think LRIs are a terribly exact science, at least not to the degree that refractive surgery demands.
Dr. Woodhams

“I use Dr. James Gills’ (M.D.) LRI technique: ww.stlukeseye.com/professionals/lri_nomogram.htm.
Shannon M. Wong, M.D.
Austin, Texas

“I’d like to offer another pearl: Correct only corneal astigmatism on topography, not refractive astigmatism. For the amount, I use the sim-K from the topography. For the axis, I use the Maloney best fit axis. If your topography system does not compute this, set your color scale to “normalize,” print out a hard copy, and visually draw a straight line on what appears to be the steepest axis.
Dr. Singer

I suggest Dr. Nichamin’s nomogram. Arcuate cuts with a square tip are possibly better. At 7 mm or 8 mm you’re performing an astigmatic keratotomy, which requires a different nomogram. You’ll have to determine just how far anterior to the limbus you want to go and be consistent so you can fine-tune the nomogram. Many will advise performing the LRI at end of the case, but I prefer to do it right up front. If the incision is temporal, treat it like a Langerman hinge incision.
Decide whether you want to perform pachymetry because this may make for a tighter cluster of results, but if your goal is to simply reduce cylinder, you can do without. Start conservatively because if you under-correct, you have still improved the situation.
Consider adjusting IOL power and be sure to have a drawing of your planned incisions in the room because nothing is worse than increasing the cylinder by misplacing incisions—except possibly flipping the axis by overcorrecting.
Jon-Marc Weston, M.D., F.A.C.S.
Roseburg, Ore.

In addition to what has already been said by other experts, I feel that performing videokeratography (VKG or corneal topography) is essential in the planning of these procedures. Not only does VKG provide us with guidance with respect to the type of astigmatism that we're dealing with, but also allows detection of forme fruste or subclinical keratoconus patients, which may not be ideal candidates for LRIs.
Finally, I'd like to mention a few words regarding terminology. At meetings and journal articles, there occasionally appears to be a confusion between the terms "axis" and "meridian" when discussing corneal astigmatism in general, and in particular when referring to LRIs. Axis corresponds to the straight line which determines the orientation of the cylinder (i.e., cylinder or cylindrical axis). As such, and being a straight line, an axis cannot be steep or flat. It can only be straight. Meridian, on the other hand, does correspond to the shape of a particular sector of the cornea. As such, when a more pronounced curvature is present, we can talk about a steep meridian.
When a lesser curvature is encountered on the cornea, then we refer to it as a flat meridian.  Thus, when deciding or reporting where to place limbal relaxing incisions, it should be mentioned that these are placed on the steep meridian of the cornea.
Of course, this corresponds to the axis of the cylinder in PLUS cylinder form. It should not be said that incisions are placed on the steep axis, as this is incorrect.
The December 2005 issue of Techniques in Ophthalmology (www.techniques-in-ophthalmology.com) has an excellent review of all these issues, written by Matthew S. Niemeyer, M.D., and Julio Narvaez, M.D.
Guillermo Rocha, M.D., F.R.C.S.C.
Cornea Section Editor,
Techniques in Ophthalmology
Brandon, Manitoba, Canada

It is not infrequent to see non-orthogonal steepening. I adjust my cuts so they are perpendicular to the steep hemi-meridians and also shift some of the cut to the broader steep zone if there is much difference on topography in a patient with high cylinder. This seems to give me better results.
Dr. Weston

Contact Information:
Gossman: mvgossman@astound.net
Hicks: pdhicks@iw.net
Koch: dkoch@bcm.tmc.edu
Loeffler: oculaser@bellsouth.net
Loewenthal: lloewenthal@comcast.net
McDonald: mcdonaldje@mcdonaldeye.com
Rocha: rochag@westman.wave.ca
Shugar: stareyes@gtcom.net
Singer: jack@SingerEye.com
Weston: DrW@WestonEyeCenter.com
Wong: Shannon@Austineye.com
Woodhams: TWoodhams@woodhamseye.com

ABOUT THE PHYSICIAN

J. E. “Jay” McDonald II, M.D., is the EyeMail editor. He is the director of McDonald Eye Associates, Fayetteville, Ark. Contact him at 479-521-2555 or mcdonaldje@mcdonaldeye.com. To join ASCRS EyeMail, where you can receive and exchange the most current thoughts about the hottest topics in ophthalmology, search archives, and more, log on to www.ascrs.org.