For years, many refractive surgeons have anecdotally complained that their chronic exposure to plume smoke from the excimer laser has led to a variety of health problems, including chronic bronchitis, asthma, and other respiratory ailments. Although there is no proof that the benzene, toluene, formaldehyde, and other chemicals known to be present in plume smoke have caused any health problems, the issue warrants our attention.
THE POTENTIAL FOR HARM
The dermatology literature contains several references to the hazards of breathing aerosolized plume smoke from CO2 lasers. Moreover, the National Institute for Occupational Safety and Health and the Occupational Safety and Health Administration have concluded that plume smoke should be evacuated and treated as infectious waste. In addition, investigators studying plume smoke from the excimer laser found that a potentially infectious live virus can be isolated from the plume evacuate.1
Although there has never been a documented case of an infectious agent transmitted by plume smoke, some surgeons have voiced the concern that they may be at risk. When operating on patients who are unknowing carriers of hepatitis C or hepatitis B or who hail from countries where prions taint the food supply, for example, could refractive surgeons be in danger of contracting infection? During excimer laser ablation, innumerable protein fragments from vaporized keratocytes and perhaps the occasional infectious microbe launch off the patient's corneal surface at a high velocity. As surgeons, we should consider that we carry all our patients with us in the form of microscopic particulates in our lungs.
SURGICAL MASKS
Some ophthalmologists advocate wearing laser plume masks as a precaution, but I believe these masks are essentially worthless. To be effective, the wearer would need to achieve an airtight seal around the mask with tape, and the mask would need to be replaced frequently because moisture from the user's breath rapidly degrades the filter's efficacy. These steps are impractical in the setting of a busy laser clinic. Even if perfectly effective, these masks are designed to filter out particles as small as 0.1 µm, whereas the size of many viruses and all prions is smaller. It is also important to note that surgical masks are designed to protect the patient, not the wearer.
Improving Outcomes
Although the potential health issues concern me, I have never experienced any adverse effects from inhaling excimer plume smoke. I initially became interested in plume evacuation as a potential means of improving surgical outcomes.
The microclimate above the corneal surface can have a profound impact on the rate with which tissue is ablated; for example, changes in air density and humidity are well known to affect treatment nomograms. Moreover, it may be possible to aspirate many proposed causes of DLK such as bacterial endotoxins or molecules of Betadine (The Purdue Frederick Company, Stamford, CT). Evacuating plume smoke has been shown to reduce the incidence of DLK in LASIK.2
Finally, it is well known that plume smoke can have a blocking effect on subsequent excimer pulses, so removing the plume seems to be a logical step toward establishing consistent corneal ablation.Available Systems
In my opinion, the plume evacuators integrated into existing excimer laser systems are extremely inefficient. The efficacy of an evacuation system relates mostly to the distance between the plume source and the evacuator's orifice. On current excimer laser systems, the evacuators are located too far from the plume source to effectively capture the smoke. The most efficient way to remove plume smoke and establish even corneal hydration is to control a microclimate above the patient's cornea by means of a fixation ring that features a cylindrical chamber and an evacuation port. Because evacuation flow rates can be relatively low using this type of system, corneal desiccation is less likely to occur. I have performed several thousand cases with two systems that employ a fixation ring, the Mastel Cleanroom System (Mastel Precision, Inc., Rapid City, SD) and the Dell PlumeSafe Evacuator (Buffalo Filter, Buffalo, NY).
Design
I designed the Dell PlumeSafe Evacuator with assistance from engineers at Buffalo Filter and ASICO (Westmont, IL). Our goal was to create a device that allowed manual globe fixation, superbly evacuated plume smoke, permitted even corneal hydration, and was compatible with all eye trackers. In addition, we wanted the device to have a low cost per case and be easy to use. The Dell PlumeSafe Evacuator consists of a plume-aspirating fixation ring (Figure 1) and a control unit with high performance ULPA filters (Figure 2). The evacuation flow rates are adjustable, and the system provides real-time data on the actual rate achieved. Knowing the actual flow rate is critical because loading a filter with debris can degrade flow rates and affect treatment outcomes.
Why Manual Fixation?
After using manual globe fixation extensively, I have come to appreciate how critical this underused technique is in LASIK surgery. Although all my lasers feature eye trackers, I believe that manual fixation allows superb control over the procedure. All eye trackers assume that the eye moves in an x-y plane, but the eye obviously rotates through an arc in space rather than a flat plane. The result is a small but real disparity between the actual and the tracker-assumed location of any given portion of the cornea. Manual fixation of the globe significantly limits saccadic movements, and I find that it also allows me to exert better control over head movements during laser ablation, thereby reducing the likelihood of treatment decentrations. Additionally, manual fixation can also control cyclotorsion, which none of the currently available eye trackers addresses. Aside from a surgeon's physically holding the eye in an incorrect position, I have yet to hear a compelling argument against the use of routine manual globe fixation.
Compatibility
At the ASCRS annual meeting in April 2003, I presented a study that examined the compatibility of the Dell PlumeSafe Evacuator with the eye trackers of the VISX Star S3 (VISX, Inc., Santa Clara, CA) and the LADARVision4000 (Alcon Laboratories, Inc., Fort Worth, TX).3 The prospective study examined 163 consecutive patients treated with the Dell PlumeSafe Evacuator and found that no tracking failures occurred. With the Star S3, the tracker paused for a fraction of a second on three eyes due to head movement beyond that for which the tracker could compensate. No patients treated with the LADARVision4000 experienced any tracking disruption.
Technique
Using the Dell PlumeSafe Evacuator generally requires the surgeon to adjust his nomogram. Because the device removes plume smoke so thoroughly and rapidly, the laser ablates tissue more efficiently. The degree of nomogram adjustment depends somewhat on the surgeon's current technique. I typically wipe the corneal bed with a sponge in order to achieve a uniform sheen prior to laser ablation, and I do not perform any additional wiping or drying during the ablation. In general, when using the VISX and Alcon lasers, I have found that the Dell PlumeSafe Evacuator combined with this technique achieves a 10% greater ablative effect than using the identical technique without the device. It is important to note that, although the surgeon enters a 10% smaller treatment amount into the laser when using the evacuator, he must perform depth calculations as though the full amount of tissue were being treated.
CONCLUSION
Because no firm data link a surgeon's exposure to plume smoke with any negative health effects, it is unlikely that laser manufacturers will wish to focus on the possibility of a health hazard. From an epidemiological standpoint, the number of individuals exposed to large amounts of excimer plume smoke is relatively small, and years may elapse before researchers can determine if such exposure has an adverse effect. Unfortunately, practicing refractive surgeons are the experimental group in this study. To me, it makes sense for us to take precautions.
1. Taravella MJ, Weinberg A, May M, Stepp P. Live virus survives excimer laser ablation. Ophthalmology. 1999;106:1498-1499.
2. Dell SJ. Plume-aspirating fixation rings and postoperative acuity in LASIK. Paper presented at: ASCRS/ASOA Symposium on Cataract, IOL, and Refractive Surgery; May 2001; San Diego, CA.
3. Dell SJ. Plume-Evacuating Fixation Rings and Tracker Disruption in LASIK. Paper presented at: ASCRS/ASOA Symposium on Cataract, IOL, and Refractive Surgery; April 13, 2003; San Francisco, CA.
