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| The Best Way to Straighten a Bow Tie
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| The Best Way to Straighten a Bow Tie
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| Several expert surgeons share their best tips for managing astigmatism with toric intraocular lenses.
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| Walter Bethke, Managing Editor
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Cataract surgeons say that individuals who have suffered from astigmatism their entire lives can be some of the happiest patients in your practice following toric intraocular lens implantation. However, to get them that way, you’ve got to follow certain protocols and take care when performing your preoperative preparations. In this article, several experienced surgeons share their tips for getting the best outcomes with toric IOLs.
Measuring Up
Surgeons say your ability to capture the magnitude and axis of the patient’s astigmatism is the key to getting the sharpest vision after surgery.
James Davison, MD, of Marshalltown, Iowa, uses four methods of keratometry ahead of time. “We do the keratometry manually and on an automated keratometer,” he explains. “Then we look for corroborating measurements from the simulated Ks on the IOLMaster and computerized videokeratography.” Some surgeons have begun to use the Haag-Streit Lenstar optical biometer for these measurements, as well. In addition to keratometry, the Lenstar also measures pachymetry, anterior chamber depth, lens thickness, axial length, white-towhite distance, pupillometry, eccentricity of the visual axis and retinal thickness with one scan.
Stillwater, Minn., surgeon Stephen Lane appreciates all the information the various methods bring to the table, but says manual keratometry is still the surgeon’s best friend. “In the clinical trial for the AcrySof toric lens, we used manual keratometry, and I’ve found that to be the most consistently accurate,” he says. “Not that IOLMaster Ks or topography should be discounted, but I’m very hesitant to use IOLMaster Ks as the sole determining factor for the magnitude and direction of the astigmatism. We rely much more on manual keratometry and topography. I like to see those two measurement methods correlate closely. The challenge with manual keratometry is that it’s a bit of a lost art. Even though we have automated keratometers, they don’t allow any room for adjustment or interpretation of the quality of the image you’re getting with them to determine just how accurate or inaccurate it might be. For instance, many times the topographic map may show a magnitude and axis of astigmatism, but if the overall map is irregular because of dry-eye disease, it won’t give a reliable reading.”
Dr. Lane expands on how to improve the results of manual Ks. “Essentially, you have to match up a T to a T,” he says. “They have to overlap. If the image is skewed or blurry, then you know the quality of the ocular surface isn’t very good. Maybe the patient needs some artificial tears, or maybe he needs to come back another day when he’s not as dry. Sometimes the quality of the measurement depends on when it’s done. The patient may have already been dilated and had his intraocular pressure checked with Goldmann tonometry, so the surface may be distorted and he’ll have to come back. In fact, if we and the patient determine he’s going to receive a lifestyle lens, either toric or presbyopia-correcting, we ask him to come back another day to get the measurements taken. That way, we know we have a fairly pristine cornea and, if there is ocular surface disease, we can treat it ahead of time.”
Robert Osher, MD, professor of ophthalmology at the University of Cincinnati and medical director emeritus of the Cincinnati Eye Institute agrees that, when it comes to precise identification of the steepest axis, manual keratometry by an experienced person is the most accurate method. “I have two technicians repeat it,” he says. “The second-most accurate method is the IOLMaster or the Lenstar, with topography being the least accurate. However, topography helps eliminate irregular astigmatism and keratoconus, which are essential to know. Topography is also helpful in confirming the amount of cylinder. The least helpful is the patient’s refraction because, in the presence of a cataract, it’s going to be highly inaccurate. The patient’s spectacles aren’t helpful either. However, if the patient has high cylinder I always check the axis in the old glasses.”
Surgeons say it’s also important to note the sources of the astigmatism. “Many patients have a lot of artificial against-the-rule astigmatism in their refraction and their glasses because of the presence of the cataract,” says Chicago surgeon Randy Epstein. “If you look at the topography and the IOLMaster and find that the patient has substantially less—or more—than on his refraction, you always have to go with those two measurements because that’s what you’re going to be left with after the cataract surgery, and any I'm - pact from lenticular astigmatism will be gone. Similarly, if a patient has a lot of topographic astigmatism, say withthe- rule, and almost no astigmatism in his glasses or on refraction, that generally means that he has induced againstthe- rule astigmatism from the cataract that’s negating it and making it look as if he’s got no significant astigmatism.”
If a patient is a candidate, knowing how much astigmatism your cataract wound induces may affect your approach to the procedure. “Wound placement plays a role,” says Pit Gills, MD, of Tarpon Springs, Fla., who primarily uses the Staar toric lens in his patients. “Whether the patient has with-the-rule or against-the-rule astigmatism will determine if the wound’s going to work in my favor or not. For instance, if I had a patient with 1.7 or 1. 5 D of with-the-rule cylinder, I know that my temporal wound will increase that, so I’ll probably use the toric lens, especially if the patient has dry-eye problems that will make a limbal relaxing incision less desirable. However, if the patient has against-the-rule astigmatism, I know my temporal wound will decrease the astigmatism, and I don’t really want to use a toric lens in that case. If a patient has a good corneal surface, I may do an LRI nasally and then not have to worry about managing lens rotation afterward.” Dr. Gills says this is an issue because about a fifth of his Staar toric lenses rotate postop.
Cincinnati surgeon Edward Holland also uses the effect of his incision in conjunction with the toric lens. “I know that my induced astigmatism is about 0. 4 D,” he says. “So, if I’m implanting the lens at the oblique axis, during my surgical planning the AcrySof toric lens calculator [acrysoftoriccalculator.com] will tell me how much residual astigmatism I’ll have, allowing me to move my incision toward or away from the axis of the lens to enhance or reduce the lens’s effect.”
Finer Points of Marking
Since being off-axis with a toric lens can result in a decrease in the treatment effect, many surgeons take pains to be as accurate as possible when marking meridians and the toric axis preop.
Dr. Osher puts a premium on precise marking. “The standard method for marking in the United States is the inadequate marking pen,” he says. “The ink runs and disperses, the patients are apprehensive that you’re coming at them with a marker and, by the time you get to the O.R., the marks have diffused or may even disappear altogether. It’s as insensitive as diagnosing pregnancy at eight and a half months. As an alternative, in my Innovators Award lecture at the last meeting of the American Society of Cataract and Refractive Surgery, I introduced a technique I rely on: iris fingerprinting. I realized the iris would be an excellent reference for establishing landmarks because it has fixed crypts, nevi, pigmentation, stromal patterns and Brushfield spots. So, I helped finance software that can take a high-resolution photograph of an eye and superimpose the horizontal and vertical meridians on the image. Using this software, on the monitor I can move a cursor and place it on any landmark on the iris and the program will tell me at what meridian that landmark is located. Finally, I can place a gold line [my goal line] at the meridian at which I want to orient the axis of the toric lens. I can then print out the image and take it with me to the O.R.” The software is made by Micron Imaging Systems (Pegram, Tenn.). A similar program is soon going to be released by Haag- Streit, as well.
Dr. Osher then places a semi-lunar, open marker adjacent to the limbus and precisely aligns the meridians at zero and 90 degrees. “Or, if the patient has an iris crypt at 36 degrees, it’s then very easy for me to orient the semi-lunar marker to identify the intended axis for toric lens alignment,” says Dr. Osher. As a marking aid, Dr. Osher uses a small point cautery device that he designed to leave two tiny white dots on the conjunctiva on the steep axis. “I can then orient the toric lens at the end of the surgery along the axis marked by those two white dots.”
For marking, Dr. Lane prefers to use a device he helped develop, the Nuijts-Lane Preop Toric Reference Marker (ASICO). “Essentially, it’s for marking the 3 and 9 o’clock positions, but it also has a little level on it, just like the yellow level you’d use for leveling a wood project,” Dr. Lane explains. “You line up the little bubble in the level so that it bisects the line, and now you know you’re perpendicular to the floor and the eye, and you can accurately mark the 3 and 9 o’clock positions with a marking pen. It leaves a fine little line at the limbus that acts as your reference point.” Dr. Lane has no financial interest in the marker.
Though surgeons may take different paths to achieve accurate toric correction, the common thread running through their advice is to make the initial marks with the patient sitting up to negate any cyclorotation effects.
Dr. Gills says the Staar toric’s propensity for rotation influences many of the initial steps. “I used to mark the eyes, but I eventually stopped because the rotation rates were about the same either way,” he says. “I use my best judgment as to what is the right axis with the patient on the operating table. Typically, the limbus has pretty good landmarks—the actinic changes from sun exposure—to use for 0 and 180 degrees. Then, postoperatively, I’ll use my slit lamp to check the lens to make sure it’s truly on axis.”
The Surgery
Here are surgeons’ tips for implanting the lens, making sure it’s on-axis and managing residual astigmatism.
First, surgeons say it’s helpful to have a printout of the preop calculations, especially the correct axis, on hand during the procedure, perhaps even taped to the microscope so you can see it at a glance. They note that the actual implantation is similar to non-toric IOLs, except for having to align the lens with the astigmatic axis.
“A trick for getting the lens on the proper axis is to remove the viscoelastic behind the IOL,” says Dr. Holland. “This is because residual viscoelastic behind the lens can cause it to tip a little, or, as the viscoelastic moves, it can also move the lens. The other step is to make sure the haptics have completely unfolded. There will be some adherence to the bag, and you can tell when you push on the lens whether the haptics have unfolded and the lens is then going to stay in that meridian.”
Surgeons also like to allow for some rotation during the removal of the viscoelastic, so they won’t put the lens in the final position right away. “I usually leave about three clock hours of dialing remaining, then empty out the anterior chamber with irrigation/aspiration, so the eye’s been effectively evacuated of viscoelastic,” says Dr. Epstein. “I’ll go behind the lens with BSS and irrigate out the viscoelastic that’s trapped there, as well. Many times, when you’re getting the viscoelastic out of the eye at the end of the case, the lens will rotate, and it may actually end up close to its final position, so you should allow for a little residual rotation. However, if the lens doesn’t rotate during viscoelastic removal, simply fill the eye with BSS and rotate with that rather than viscoelastic. This avoids getting stuck in a cycle of injecting more viscoelastic to rotate the lens only to have it move again as your remove that viscoelastic.”
In an effort to get the most effect from the lens and his other astigmatism treatments, Dr. Lane has been using the new Orange intraoperative aberrometer (WaveTec Vision). “You can take an Orange measurement after you put the lens in and it will tell you to rotate it 10 degrees clockwise or counterclockwise, for instance,” he says. “I think there will continue to be enhancements to the instrument, and it will continue to improve in accuracy to the point where it will be vital in really nailing down the postop refraction.”
If you expect there to be residual astigmatism after the lens is implanted, several surgeons recommend incorporating an LRI or two into your procedure. “At the beginning of the case, I’ll map out where my cataract incision is going to go, where the toric lens is going to be and where the LRIs are going to be placed,” says Dr. Holland. “I do the LRI at the beginning of the case, right after the stab incision. I’ve found I can get 1.5 to 2 D with paired LRIs.”
Dr. Gills has a tip for users of the Staar toric. “If you put one in a patient with a Morcher ring, the lens can get hung up on the ring,” he warns. “Try to get all of the lens injected into the bag at once. Sometimes, with a plate lens, you might allow the proximal end to sit up on the iris and then push it in afterward. But, with a Morcher ring present, the plate lens can capture the ring as you push the proximal end down, and it can dislodge the ring into the bag so that it’s wrapped around the lens.” To remove the ring, Dr. Gills says you bring the plate back up out of the bag and have to work the Morcher ring from around the lens. You then take the ring out before pushing the lens back down.
Managing Postop Rotation
In some patients the toric lenses will rotate postop. Here’s how to manage these cases when they occur.
Dr. Davison performed a study of 850 AcrySof toric implantations at his practice, and found that 1 percent [9 implants] rotated postop. “It was usually myopic patients with really large eyes,” he says. “They rotated an average of 47 degrees. To reposition them, I used BSS on a syringe for two of the cases. For the remaining seven, I opened the original incision, put in ProVisc, and used an I/A tip and a Lester hook to rotate the lens. I believe you can use either method, and I recommend using a cohesive viscoelastic on the surface, not in the capsular bag. Make sure that all the viscoelastic is removed afterward.
“It’s an unusual procedure to do,” Dr. Davison adds. “You don’t have to do it very often. I think surgeons who try to do it without the viscoelastic are going to be challenged, but I don’t think that challenge is necessary; you can do it with visco and just the I/A, similar to the way you rotated the lens originally.”
For repositioning the Staar toric lens, Dr. Gills uses a TB syringe. “If I need to rotate the lens 15 degrees clockwise for instance, I’ll go in with the TB syringe at the 15-degree mark where I want to be,” he says, “and I’ll then rotate the lens and move it so that it lines up with that 15-degree position.”
Overall, these surgeons have been pleased with toric lenses. “I believe that all surgeons should feel comfortable with a toric lens,” says Dr. Osher. “If a patient is a good candidate and asks me what I would do, I tell him that I’d have the toric lens. When asked why, I reply, ‘When I remove a cataract in a patient without astigmatism, he sees as well as he did before the cataract developed. But when I remove a cataract and replace it with a toric lens in someone who has had significant astigmatism, he not only sees as well as he did before the cataract developed, he sees better than he has in his entire life without his glasses.’ These toric-lens patients are the happiest patients in our practice.”
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Vol. No: 17:1Issue:
1/1/2010
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JULY DIGITAL EDITION
Review of Ophthalmology
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