Until recently, most ophthalmologists have largely ignored the plume (smoke) created by excimer laser corneal ablation. There are two aspects of the plume that surgeons need to consider. First, what are the health effects of this material for the surgeon and staff who are present during the procedures? Second, how does the plume affect the delivery of the laser treatment to the cornea?
During a refractive surgery procedure, ablated corneal particles are suspended over the surface of the cornea. These plume particles scatter the subsequent refractive laser pulses and attenuate the laser energy that strikes the corneal surface. This effect can lead to variable results. The central islands associated with broad-beam lasers are due to the effect of the plume.1 By removing the plume from the pathway of subsequent laser strikes, more accurate treatment profiles can be expected. This finding was confirmed in a study using the EC-5000 laser (Nidek Inc., Fremont, CA) in which significantly better patient outcomes were achieved when the plume was evacuated from the corneal surface.2VIRAL TRANSMISSION POSSIBLE
It was assumed in the early years of excimer laser corneal treatments that the plume was safe, because the laser worked by precisely breaking molecular bonds rather than burning tissue. When considering laser effluence, there is cause for concern about infection as well as the possibility of developing reactive airway disease and/or bronchitis for laser-room personnel. It has long been known that live viruses can be isolated from the CO2 laser plume, specifically, papilloma and papova virus. Incidentally Pseudorabies virus did not grow on a culture plate suspended above a previously inoculated plate exposed to excimer energy.3 However, a study4 using oral polio vaccine virus showed that the virus survives excimer laser ablation, as the live virus is isolated from the plume. Using eyebanked corneas, the same group showed that potentially respirable particles are created during excimer corneal ablation.5 The possible transmission of prions has not yet been studied, but viral transmission through the respiration of the corneal excimer laser plume is possible.
Respirable particles with a size of 0.5µm or more could form deposits on the walls of the nasopharynx, trachea, and bronchial bifurcations. Those of less than 0.2µm could settle in respiratory bronchioles and alveoli, although particles smaller than 0.1µm are absorbed directly into the bloodstream. A study of plume particles collected on the filter of a Mastel Clean Room plume evacuator (Mastel Precision Instruments, Rapid City, SD) by Glen A. Stone, PhD (written communication, March 2003), revealed a distribution of particle size from 0.85 to 0.1µm. Mass spectrometry of the filter extracts revealed proteinaceous fragments that were classified as likely degraded proteins and/or nucleic acids. The proteinaceous fragments have molecular weights of up to 5kd. Proteins of this magnitude or greater are known to be human pathogens.6 Based on these findings, it is sensible to filter the plume particles down to a size of at least 0.1µm.SURGICAL MASKS ARE NOT adequate
The laser-plume surgical masks that are used by a few excimer surgeons generally have a pore size too large to safely filter the respirable particles present in the excimer laser plume. The plume filter on the S4 laser (Visx Inc., Santa Clara, CA) has a pore size of 0.22µm, which is also not sufficient to remove the respirable particles. Furthermore, the ejection velocity of the particles from the ablated corneal surface is 1500m/s. Therefore, a plume evacuator must be located at the corneal surface to be effective, and it must have the ability to filter particles down to a size of at least 0.1µm. The evacuator must remove the plume without adversely affecting the laser treatment, permit the surgeon to observe and control the treatment, and allow normal function of the laser tracker.CONFIGURATION OF THE DELL PLUMESAFE
The Dell Plumesafe System (Buffalo Filter, Buffalo, NY) utilizes 0.1-µm VLSI-ULPA (very large scale integration-ultra low penetration air) carbon filters and will block the most worrisome infectious particle sizes. The device is configured with a nonreflective black handpiece that rests upon the limbal surface during a refractive surgery procedure (Figure 1). A single flexible plastic tube connects the handpiece to the base unit. The surgeon holds the handpiece with one hand during the procedure, while his other hand free to control the laser or utilize other instruments if necessary. The bottom of the handpiece is textured to help the surgeon stabilize the eye during the procedure, a helpful maneuver in patients who have trouble fixating. Patients do not complain of discomfort, and there is no increased redness or subconjunctival hemorrhage postoperatively associated with Plumesafe use. Furthermore, the unit is quiet.CONCLUSION
In summary, to ensure surgeon and staff safety and improve patient results, the Dell Plumesafe is a useful tool for excimer refractive surgery. I find it easy to use and economical. I believe that refractive surgeons should no longer ignore the hazards of an excimer laser plume. n
Nancy A. Tanchel, MD, is Medical Director at the Liberty Laser Eye Center in Vienna, Virginia. She states that she holds no financial interest in any product or company mentioned herein. Dr. Tanchel may be reached at (571) 234-5678; firstname.lastname@example.org. Noack J, Tonnies R, Hohla K, et al. Influence of ablation plume dynamics on the formation of central islands in excimer laser photorefractive keratectomy. Ophthalmology. 1997;104:823-830.
2. Charles K. Effects of laser plume evacuation on laser in situ keratomileusis outcomes. J Refract Surg. 2002;18(suppl 3):340-342.
3. Hagen KB, Kettering JD, Aprecio RM, et al. Lack of virus transmission by the excimer laser plume. Am J Ophthalmol. 1997;124:206-211.
4. Taravella MJ, Weinberg A, May M, Stepp P. Live virus survives excimer laser ablation. Ophthalmology. 1999;106:1498-1499.
5. Taravella MJ, Viega J, Luiszer F, et al. Respirable particles in the excimer laser plume. J Cataract Refrac Surg. 2001;27:604-607.
6. Liu Y, Mayo GL, Baribeau AD, et al. Solid particles in excimer laser plume. Poster presented at: The Association for Research in Vision and Ophthalmology Annual Meeting; May 9, 2002; Fort Lauderdale, FL.