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Preoperative cone location appears to affect topographic and visual acuity outcomes of CXL, according to study results.
Chicago-Preoperative cone location appears to affect topographic and visual acuity outcomes of cornea collagen crosslinking (CXL), according to results of a study presented by Steven Greenstein, BA, at refractive surgery subspecialty day during the annual meeting of the American Academy of Ophthalmology.
Greenstein reported findings from analyses of data collected in a single-center study including 99 eyes of 76 patients followed for 1 year after standard CXL. The indication for treatment was progressive keratoconus in 66 eyes and ectasia in 33 eyes.
Overall, treatment resulted in significant mean reductions in both maximum K (–1.7 D) and average K (–0.9 D) comparing baseline and 1-year values, while both uncorrected visual acuity and best spectacle-corrected visual acuity (BSCVA) improved by an average of about 1 line at 1 year.
"Further investigation is required to determine the effect of preoperative cone location on other CXL outcomes and to determine if the CXL treatment should be more focused on preoperative cone location," said Greenstein, pre-residency research fellow at the Cornea and Laser Eye Institute-Hersh Vision Group, Teaneck, NJ and medical student at the Albert Einstein College of Medicine, Bronx, NY.
The CXL study was undertaken at the Cornea & Laser Eye Institute, CLEI Center for Keratoconus, Teaneck, NJ. Peter S. Hersh, MD, FACS, director of the Cornea & Laser Eye Institute and clinical professor of ophthalmology, UMDNJ-New Jersey Medical School, Newark, NJ, is the principal investigator.
The three cone location groups were defined by whether the maximum K was located within a central 3-mm, 3 to 5-mm, or >5-mm central optical zone. There were 42 eyes with centrally located cones, of which 34 (81%) had keratoconus and eight (19%) had a diagnosis of post-LASIK ectasia. The middle group was composed of 24 eyes with keratoconus (75%) and eight eyes with ectasia (25%), and there were 25 eyes with the most peripherally located cones, including only eight eyes with keratoconus (32%) and 17 eyes with ectasia (68%).
Results from the topographic analyses showed a mean decrease in maximum K of –2.6 D in eyes with the centrally located cones versus only –0.4 D in those with the most peripherally located cones; mean changes in average K for these two groups were –1.8 and –0.3 D, respectively. Mean logMAR BSCVA improved by –0.14 (~1.5 lines) in eyes with the centrally located cones versus –0.08 (<1 line) in the other two groups.
"Patients in all three groups achieved significant improvement in BSCVA and all had an equivalent likelihood of topographic stability at 1 year after CXL," Greenstein said.
Discussing possible reasons for the cone location-dependent differences in outcomes, Greenstein suggested the explanation may reflect a difference in response to CXL based on either cone location or underlying diagnosis.
"Perhaps the biomechanical forces after CXL may be more symmetrically distributed across the centrally located cones and this symmetric stretching of the cone may induce more topographic flattening and therefore more improvement in BCVA," he said. However, another possibility for the between-group differences may be related to the difference in diagnosis distribution between groups because the eyes with the most centrally located cones were predominant in those with keratoconus whereas ectasia was the predominant diagnosis for the group with the most peripherally located cones.
"Perhaps the results of this study reflect an inherent response difference between these two diagnostic entities with a more robust response of keratoconus to CXL," Greenstein said.
In addition, the energy profile of the UV light, which may be more powerful centrally than peripherally, could also contribute to the findings in the study.
Peter S. Hersh, MD, FACS
Greenstein has no financial interest in the subject matter. Dr. Hersh is a consultant to Avedro, manufacturer of a riboflavin/UVA system for accelerated CXL (KXL Accelerated Cross-Linking).