In this installment of Interventional Mindset, Preeya K. Gupta, MD, sits down with William Trattler, MD, to review how surgeons can screen patients for and manage corneal ectasia after refractive surgery.
Dr. Trattler is a board-certified refractive, corneal, and cataract surgeon at the Center for Excellence in Eye Care in Miami, Florida, where he also serves as the Director of Cornea.
Diagnostic tools for identifying corneal ectasia
Corneal ectasia includes a group of conditions that cause the cornea to thin and bulge outward, which can occur naturally (e.g., keratoconus) or as a complication of corneal refractive surgery.1 Consequently, having accurate pre-operative diagnostic testing is critical to screening patients appropriately for refractive surgery.2
Drs. Gupta and Trattler explained that their current go-to tool for evaluating the corneal surface in refractive surgery candidates is the Pentacam (OCULUS) corneal tomographer. This is in part because it features a Belin/Ambrósio enhanced ectasia display, which can produce a BAD_D (Belin/Ambrósio enhanced ectasia display total deviation value) score.
The BAD_D is a multivariate index that integrates anterior elevation, posterior elevation, and pachymetric data to provide a complete overview of the corneal shape.3 Dr. Trattler added that he also analyzes the percentage thickness increase (PTI) to understand the progression of thickness from the thinnest point of the cornea to the periphery.3
Chart review of patients who underwent corneal cross-linking
Recently, Dr. Trattler analyzed the medical records of patients he performed corneal collagen cross-linking (CXL) on and found that 82% had no history of any type of eye surgery, and in the 18% that did, 97% underwent laser assisted in-situ keratomileusis (LASIK) and 3% had a history of photorefractive keratectomy (PRK). He noted that LASIK may be a risk factor for corneal ectasia, potentially because of the flap created during the procedure.4
For a discussion on when Drs. Gupta and Trattler use epithelial thickness maps, make sure to watch the full interview!
Surgical pearls for performing corneal cross-linking
Based on findings from a 2008 study by Dawson et al., Dr. Trattler explained that the flap created during LASIK provides little to no strength to the cornea.5 Consequently, when he is doing corneal CXL, he aims to go deeper than the flap, as the goal is to get good penetration of the riboflavin into the cornea and then complete the CXL procedure.
Further, during the procedure, he prefers not to center the light treatment on the center of the cornea, and instead, he looks at the Pentacam to identify the thinnest spot on the cornea, and that becomes his goal for centering.
For patients who have corneal thinning that is inferior to the center of the cornea, he asks the patient (who is lying supine) to look up (i.e., above the light) so he can access and treat the lower part of the corneal. He explained that because the beam is 9mm in diameter, if surgeons perform corneal CXL centrally and the patient has more inferior disease, they will not effectively treat the entire weakened cornea.
Figure 1: CXL procedure with iLink UV light technology demonstrating centration on the lower part of the cornea in a keratoconus patient with thinning of the cornea located inferiorly.
Figure 1: Courtesy of William Trattler, MD.
Corneal ectasia in cataract patients who underwent LASIK
Dr. Gupta highlighted that many patients who had LASIK right when it came out (i.e., 1999) are now coming in for cataract surgery, creating an interesting dilemma if they come in with corneal ectasia.
In patients who underwent myopic LASIK, Dr. Trattler explained that he tends to see a flat central area (usually marked blue on Pentacam) with peripheral steepening. He added that in his professional medical opinion, if surgeons see irregularities in this shape of the cornea in patients with a history of LASIK, one potential cause can be early keratoconus (or post-LASIK ectasia).
Should I do corneal cross-linking or cataract surgery first?
Dr. Gupta explained that some of the deciding factors for whether she does corneal CXL or cataract surgery first are the amount of astigmatism and how irregular the cornea is. If the patient’s cornea is very irregular, she has found that it is unlikely that CXL will make them “glasses independent.” However, if the patient has a regular enough cornea that they could be fitted with a toric intraocular lens (IOL) later, she recommends corneal CXL first and cataract surgery second.
Dr. Trattler noted that if a patient has a very mild cataract, he considers cross-linking first, but otherwise, he focuses on extracting the cataract first and leaving them a bit myopic because corneal CXL can lead to a mild hyperopic shift over time.6
For a deeper dive into how surgeons can use Pentacam to identify progression in patients with corneal ectasia, watch the full interview!
Conclusion
Drs. Gupta and Trattler emphasized that having a good corneal tomographer is critical to following and screening patients for corneal ectasia.
While advancements in diagnostic technology have helped reduce the incidence of corneal ectasia after corneal refractive surgery,7 it is still important that surgeons know how to manage it—especially given the increasing number of patients with prior refractive surgery.
