Eyeworld

EW FEATURE 86 Corneal collagen crosslinking • September 2016 AT A GLANCE • Factors to consider when deciding whether to pursue crosslinking include patient age, clear signs of progression, and how the patient is doing with his or her current visual strategy. • A patient who already has severe keratoconus may not be the best candidate for crosslinking. He or she may already need a corneal transplant. • When talking to patients about crosslinking, many surgeons emphasize its goal of stopping progressive keratoconus. It's also important to discuss with patients the visual recovery associated with crosslinking. by Ellen Stodola EyeWorld Senior Staff Writer because crosslinking could affect their endothelial function. Very thin corneas have a higher risk, although this isn't necessar- ily a contraindication. Physicians could still consider crosslinking for patients with very thin corneas if the alternative is a corneal trans- plant. Dr. Randleman added that he wouldn't recommend crosslinking to patients who are stable and doing well with their current situation refractive correction. Post-LASIK ectasia patients Crosslinking is recently approved for post-LASIK ectasia. "Those patients tended to do well when we treated them in the first clinical trial," Dr. Randleman said. For patients who have developed ectasia after LASIK, the question is when it happened. Those patients may or may not ben- efit tremendously from crosslinking if they developed ectasia many years ago and are now stabilized, he said, adding that physicians should be aggressive about treating those who have developed ectasia after LASIK early in the process. Pellucid patients For pellucid patients, an ectatic corneal disorder in the same fam- ily as keratoconus and post-LASIK ectasia, Dr. Randleman said these are good candidates for treatment with crosslinking. Many diagnosed with this actually have a form of keratoconus, but it looks different from average keratoconus, Dr. Randleman said. Pellucid patients need a larger UV optical zone and are usually more aggressive, Dr. Rocha said. You want to treat them all the way close to the limbus, she said. Customized corneal crosslinking may be a good option for these cases. Patients with RK Addressing patients with RK is a different process, Dr. Randleman said. Since there is an incision made in the cornea, the cornea is weaker by design. It's different tissue because the crosslinking would have to cross the bridge of that incised tissue to have an effect. It's also a different cornea, he said. These patients have a fluctu- ating, weaker cornea because they've had surgical incisions. profile maps. Thinner epithelium is observed over areas in which the anterior stromal curvature is steep and the corneal surface is elevated. Thicker epithelium is observed in areas of stromal thinning. Consid- ering that the cytotoxic irradiance threshold for endothelial cell dam- age in corneal collagen crosslinking may be reached with a stromal thickness of less than 400 µm, direct measurement of epithelial and stro- mal thickness within the treatment zone may improve the safety profile by ensuring that the minimum residual stromal bed is present for standard epithelium-off crosslinking procedures. The customized pachy- metric-guided epithelial removal technique may overcome the lim- itations of the preoperative corneal pachymetry, expanding the appli- cation of the procedure in patients with significant regional stromal loss and epithelial remodeling. Dr. Suh said she uses both qual- itative and quantitative measures when determining whether she should use crosslinking for a kerato- conus patient. Qualitative measures include worsening vision or glare, and quantitative measures include tomography, mean keratometry, maximum keratometry, pachymetry, and other measurements. She added that when deciding whether or not to treat, the patient should show definite signs of keratoconus. "A young patient often is still progress- ing, so these are the patients who I think benefit the most from cross- linking," she said. Sometimes crosslinking is not the best option There are also instances when cross- linking would not be the best choice for a particular patient. Dr. Rocha said she would not use crosslinking in patients who already have severe keratoconus and bad visual prog- nosis. For these patients, it might be more appropriate to do a corneal transplant, she said. Dr. Suh added that crosslinking may not be the appropriate choice for a patient who has been stable for awhile and has good vision with contacts and is content overall with his or her best correctable vision. Those with severe keratoconus with significant thinning of the cornea may also not be good candidates patient age, clear signs of progres- sion, and how the patient is do- ing with his or her current visual strategy. Crosslinking is approved in the U.S. specifically for documented signs of progression of keratoconus. Another important factor to consider is patient age. If a patient is diagnosed at a young age with ker- atoconus, especially before the age of 25, it is usually better to treat at diagnosis rather than wait for signs of progression. Dr. Randleman said that another patient group to consider are those who are not doing particularly well with their current visual strategy. They may not be seeing well with glasses or tolerating their contact lenses well, or could be progress- ing to a point where the next step would be a corneal transplant. For some patients, he said, if you make the cornea a bit flatter or a bit more stable, they could be improved in glasses or contacts. Many parameters for deciding when to do crosslinking still need to be improved upon, Dr. Randleman said. More research into crosslink- ing is needed, especially regarding what metrics are the best to define progression. The maximum keratometry value is used to tell how steep the cornea is in a particular location, but this is not always the best metric, he said. Physicians can also use correct- ed acuity and look at cornea thick- ness, but these are not particularly helpful to determine progression or regression. There's a difference between procedures in the U.S. and in Eu- rope, Dr. Rocha said. In her expe- rience, you don't necessarily need to wait for progression because you want to treat the patient before he or she gets much worse. This is particularly important in young patients. Dr. Rocha said it's also import- ant to decide whether epi-off or epi-on crosslinking will be the best option for the patient. She uses spec- tral domain OCT to determine this. Spectral domain OCT measures the anterior and posterior corneal curvature in addition to qualitative and quantitative analysis of the re- lationship of the corneal epithelium and stroma that can be expressed as total and corneal epithelial thickness Surgeons discuss when to offer crosslinking as well as the conversation to have with patients about the procedure W ith its recent approval in the U.S., crosslink- ing has become avail- able for an even larger number of patients. However, there are still a number of factors to consider when deciding which patients are the right candi- dates for this treatment. J. Bradley Randleman, MD, professor, De- partment of Ophthalmology, Keck School of Medicine of USC, and director of cornea, external disease and refractive surgery, USC Roski Eye Institute, Los Angeles; Leejee Suh, MD, Miranda Wong Tang as- sociate professor of ophthalmology, and director, Columbia University Laser Vision Center, New York; and Karolinne Maia Rocha, MD, PhD, director of the cornea service, Med- ical University of South Carolina, Charleston, South Carolina, com- mented on their experiences with crosslinking and how they decide when it's the best option. Crosslinking in a keratoconus patient Dr. Randleman said there are three factors he looks at when deciding whether to pursue crosslinking: Deciding when to use crosslinking

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