Management of the irregular cornea
Tips for using topographic ablation
by Ellen Stodola EyeWorld Staff Writer
Topographies of one of Dr. Barsams patients pre and post topography-guided PRK. Prior to the procedure, the patient had moderately severe keratoconus with 5 D of irregular astigmatism. After topography-guided PRK with the WaveLight system (Alcon), the astigmatism was halved and is more regular. The patient had improvement in both unaided and best spectacle-corrected visual acuity. Source: Allon Barsam, MD
Physicians discuss which patients are strong candidates for topographic ablation
As topographic ablation becomes more popular worldwide, its important for physicians to know which patients may be the best candidates, which patients are not the best candidates, and when it will benefit them most to use this technology. Karl Stonecipher, MD, Greensboro LASIK, Greensboro, N.C.; Allon Barsam, MD, AB Vision, London; and Daniel Durrie, MD, Durrie Vision, Overland Park, Kan., discussed when they would use topographic ablation, pearls to ensure a good topography, and when topographic ablation may be used with certain conditions.
When to choose a topographic over a wavefront or optimized ablation
Dr. Durrie was a clinical investigator for the topography-guided study in the U.S. One of the most important things about this new system is for surgeons to understand that this is different from doing diagnostic topography, he said. Topography helps in diagnostics to make decisions, he said, but if theres a bad test, it wont hurt anyone as a diagnostic tool. However, using it now as a therapeutic tool, Dr. Durries worry is that physicians will think they already know how to use it, even though there are different considerations. You need to pay a lot more attention to the quality of the image, he said. Be sure that its a high quality topography before using the data.
Patients who have asymmetric topography do well because the topography will drive the asymmetric ablation pattern, he said. However, Dr. Durrie said its important to note that all of the patients in the U.S. clinical trial had virgin eyes, so there were no enhancements or touch-ups. Its approved for treating virgin eyes who have asymmetric topography, he said. One worry, he said, is that some patients may not be the best candidates for this procedure, and if these patients dont get good results, the procedure could get a bad reputation. Topographic ablation could work for patients who have had previous surgery, but its important to remember that there is currently no U.S. data on this.
Dr. Barsam currently only uses topographic ablations on diseased corneas that also have an irregular corneal shape and poor quality of vision as a result of this. He uses wavefront-optimized ablations in routine cases. I find wavefront scanning to be somewhat unpredictable on diseased corneas and therefore do not do wavefront-guided treatments on diseased corneas, he said. It goes without saying that either with Contoura [Alcon, Fort Worth, Texas] treatments or wavefront-guided treatments, you must first be able to capture an accurate, reproducible, and complete diagnostic measurement, Dr. Stonecipher said. Otherwise, the outcomes could suffer. He suggested using wavefront-guided treatments for patients who have higher-order aberrations of 0.4 microns RMSH or higher and no lenticular issues. As for Contoura, he follows the guidelines and treats over 18 years of age and up to 9 D of myopic astigmatism and up to 3 D of astigmatism.
Pearls for assuring a good topography to treat
As physicians are beginning to use topographic ablation more frequently, Dr. Durrie said its important to understand a few major points. First, he said that its possible for patients noses to get in the way, so the surgeon simply has to know to tilt the head. Some patients dont open their eye wide enough, so you need to help them but without putting pressure on the eye and distorting it. You need to make sure the tear film is really good, he added. Also, surgeons need to be able to look at the Placido disc rings on the topography device and be able to see the raw data. This treatment is all about the measurement, Dr. Stonecipher said. If you dont have a good picture, you cant get a good outcome. He finds that in some patients, because of their anatomy, he ends up reverting back to a wavefront-optimized treatment. Dont let the computer interpolate the data, he said. That is very important. Taking multiple pictures will help to ensure reproducibility and eliminate noise. Make sure the ocular surface is healthy, and definitely treat any ocular surface disease prior to measuring and treating patients, Dr. Stonecipher said.
Additionally, positioning the patient in the device is extremely important. In some cases it will take more than one person to take the picture in those instances where patients cant open their eye wide enough, he said. If the lashes are in the way, we have used an eye lash curler to get them out of the way. The ocular surface must be optimized by medical therapy in advance of the treatment day, as a good topography scan is reliant on a healthy tear film, Dr. Barsam said. The WaveLight laser (Alcon) analyzes the Pentacam (Oculus, Arlington, Wash.) images and grades them according to quality; he then reviews them all before treating to ensure that they correspond and are of good quality.
Optimizing the ocular surface
The very first thing to consider in optimizing the ocular surface is the tear film. Roughly one-third of my patients will come in with the diagnosis of dry eye or ocular surface disease, Dr. Stonecipher said. If needed, I will place these individuals on cyclosporine and discontinue their contact lens wear until the surface is normalized. In some cases, he will use punctal occlusion after treating inflammation, and if meibomian gland disease becomes a problem, an antibiotic of corticosteroid may become necessary. Finally, with newer diagnostics, we are seeing significant meibomian gland dropout even in younger patients, he said. If severe, I have recommended LipiFlow [TearScience, Morrisville, N.C.] treatments prior to surgery. Dr. Barsam will pretreat any meibomian gland dysfunction with a combination of nutritional supplements, hot compresses, or LipiFlow and a topical anti-inflammatory, such as cyclosporine. Be sure to treat issues like blepharitis and dry eye ahead of time in order to allow good readings, Dr. Durrie said. You also need to be fairly quick, he said, and not have the patient staring at the screen for a long time before taking the reading because this could dry out the eyes.
When not to use a topographic ablation
We cant look at this technology as a way to treat all of our previous refractive surprises and unhappy patients, Dr. Stonecipher said. We need to learn from out colleagues that this technology can create problems in this patient population, and they may be permanent problems. He recommended not treating patient with active dry eye disease.
We are currently learning from several great clinical trials where this technology can be coupled with crosslinking to help this subset of patients, he said. Patients with active systemic disease (i.e., collagen vascular, autoimmune, or immunodeficiency diseases) or ocular disease (i.e., advanced glaucoma or uncontrolled diabetes) should not be considered. Its also important to follow the golden rules of refractive surgery, Dr. Stonecipher said, to ensure that patients are good candidates. At this time, Dr. Durrie would not use topographic ablation for patients who have had previous surgery or those who have already thin corneas. He said that its important to realize that you could really get into trouble if using this technology in a patient in whom its not currently indicated. Move slow and easy with it, he said.
Topographic ablation for a patient with an irregular cornea
One option that has been used for patients with an irregular cornea, outside of the U.S., is topography- guided surface ablation and corneal crosslinking, Dr. Durrie said. Looking toward the spring, hopefully we will have both topography-guided ablation and crosslinking approved, he said. I think there will be a lot of interest in that. But currently this treatment is off-label. If the patient is intolerant of contact lenses and suffers from poor quality of vision, Dr. Barsam will use topographic ablation as an option for patients with irregular corneas. As I combine these treatments with crosslinking, they need to have a total corneal thickness of more than 425 microns to allow room for the ablation and epithelial removal before safe crosslinking, he said.
Editors note: Drs. Stonecipher and Durrie were clinical investigators on the U.S. topographic ablation clinical study. Drs. Barsam and Stonecipher have financial interests with Alcon.