Topography-Guided Laser Vision Correction
A preview of an ongoing US clinical trial for topography-guided customized ablations.
Topography-guided customized ablation treatments (T-CAT) are a new treatment modality currently available internationally and under investigation in the United States.1 A phase 3 FDA clinical trial has recently commenced to evaluate the new technology on the Allegretto Wave Eye-Q excimer laser (Alcon Laboratories, Inc.; Fort Worth, TX). What follows is general information about the procedure and preliminary details about the study.
WHAT IT IS
Conventional and wavefront-optimized excimer laser treatments place a spherocylindrical correction on the cornea. Wavefront-guided treatments measure aberrations in the optical system of the eye and change the corneal curvature to correct them. T-CAT differs from traditional procedures available in the US because they use information about corneal topography along with refractive data to design a treatment plan.
The topography-guided procedure may offer several advantages over wavefront-guided and wavefront-optimized ablations. First, because higher-order aberrations in the young eye typically arise from the cornea, it makes sense to measure and correct the cornea rather than measuring the optical system of the entire eye and then correcting aberrations on cornea. Second, T-CAT may be more accurate and reproducible than wavefront-guided measurements, especially in eyes that are highly aberrated and in most need of correction.2 Third, T-CAT may provide a more accurate correction of peripheral corneal curvature compared to wavefront-guided treatments, which are limited in coverage by the diameter of the pupil (topography-guided corrections are independent of pupil size). For these reasons, topography-guided treatments may provide a better quality of vision in both bright and dim lighting conditions than wavefront-guided treatments. T-CAT may also offer better outcomes than wavefront-guided treatments for individuals with highly aberrated corneas.3
HOW IT MAY BE USED
Topography-guided ablations may be used as a primary treatment for patients who want to eliminate their need for glasses or contact lenses. This treatment may also be used as a secondary procedure to correct eyes that are symptomatic after previous LASIK or PRK–especially those that have decentered ablations and small optical zones (see Dr. Lin’s article on page 11). Topography-guided ablations may also be effective for the treatment of patients who have undergone previous radial keratotomy or corneal transplants.
So far, about 20 patients with myopia or hyperopia have been treated as part of the ongoing FDA T-CAT clinical trial, and the early postoperative observations have been extremely encouraging. The sponsor also submitted a plan to treat patients who had visual symptoms after previous refractive surgery, but the FDA has so far not approved a protocol to do so. It is our hope that the FDA will take this opportunity to offer treatment to this small but important segment of the population that might benefit from T-CAT.
The FDA clinical trial will evaluate whether topographyguided laser vision correction provides a strategy to improve objective and subjective visual performance in patients who otherwise would receive conventional, wavefront- optimized or wavefront-guided treatments. The approval range is expected to be similar to that in existence for excimer lasers that are currently marketed in the US. Many hope that future clinical trials will include patients who are symptomatic after previous corneal refractive surgery.
TOP 5 ARTICLES FROM 2010
- DIFFICULT CASES: Severely Subluxated Pediatric Cataract in an Eye With Aniridia and Glaucoma
By Amar Agarwal, MS, FRCS, FRCOPHTH
- IOLs: How to Succeed With the AcrySof IQ Restor Lens
Six steps for excellent outcomes after cataract surgery with this multifocal IOL.
By Thomas G. Adell, MD
- Corneal Protection In Cataract Surgery
Safeguarding the cornea against disease elements and environmental challenges.
- Macular Function
Cataract & Refractive Surgery Today asked five surgeons to discuss the importance of assessing macular function in cataract patients.
By Steve Charles, MD; Samuel Masket, MD; Jay S. Pepose, MD, PHD; Richard Tipperman, MD; and William B. Trattler, MD
- Intraoperative Floppy Iris Syndrome
A systematic approach.
By Samuel Masket, MD; David F. Chang, MD