Phototherapeutic Keratectomy (PTK)...
In 1996 the U.S. Food and Drug Administration (FDA), Center for Devices and Radiological Health, gave PMA (Pre Market Approval) approval to:
LaserVision Centers, Inc. 540 Maryville Centre Drive, Suite 200, St. Louis, Missouri 63141, Phone (314) 434-6900 (Note, the company has since merged with TLC Laser Eye Centers)
to use Phototherapeutic Keratectomy (PTK) with the VISX Excimer Laser System Model C for a number of problems, including Thygeson's superficial keratitis.
However, the clinical trials (as of June 1999) had not treated anyone with Thygeson's. Here is the detailed answer I received in late June 1999, from the study's Medical Monitor, Marc G. Odrich, MD, :
"...The labeling for the VISX Excimer Laser System mentions Thygeson’s. Please note that during our clinical trials NO patients with Thygeson’s SPK were treated. Further, during training of doctors with this device we actively discourage the treatment of patients with active Thygeson’s as this is an inflammatory condition of the cornea and the condition might be exacerbated by the use of this laser. Rather the use of this laser is more appropriate in inactive (what is typically called "burned-out") Thygeson’s corneal scarring that is left after the disease has run its course. These small nebulae of scar can cause a reduction in visual acuity. This laser has the ability to remove or reduce these scars from the cornea with submicron precision..."
He added, "The excimer does not vaporize...Vaporization is referable to a heat based reaction which makes a liquid (sometimes a solid) gaseous. The excimer is not a heat based energy source but rather uses highly energetic photons to disrupt carbon-carbon bonds in a process known as photoablative decomposition. This is a relatively cool process generating little heat."
Marc G. Odrich, MD marco@visx.com. Medical Monitor, VISX, Inc., Director of Refractive Surgery, Columbia University