LASIK and SCUBA Diving
by David A. Wallace MD
People who engage in recreational, commercial or military SCUBA diving may have questions about the appropriateness of laser vision correction surgery to this particular pursuit. We present here a discussion of the relevant factors that affect and pertain to LASIK in the context of diving. I have been a certified diver for many years, and believe that having laser vision correction treatment poses absolutely no additional risk for any diving, whether recreational, commercial, or military. I make this statement based on all available data , scientific research, and vast experience of those in military service including Navy SEALs.
The following are excerpts from a series of online interchanges between eye care professionals and other experts in diving and its effect on the eye. Names of contributing participants have been removed to preserve confidentiality, as some of the posts are from physician-only discussion groups. Where Dr. Wallace has contributed personally, posts are appropriately identified. These posts date from approximately '99 and '00.
An initial question raised to the discussion group related to how long after corneal transplant surgery it might be advisable to wait before allowing SCUBA diving.
[by Dr. Wallace] Almost all pressure-related risks of SCUBA diving relate to gases, not liquids, at various pressures, levels of (dis)solution in the bloodstream, or in states of pressure change. Fortunately for us, the eye is filled entirely with liquid (absent recent retina surgery with gas insufflation) which are not compressible in the same way.
A superb online resource that addresses these various issues can be found at http://www.scuba-doc.com/diveye.htm. This site discusses a series of issues relating to diving and the eye in a clear, detailed fashion.
The website referenced does state that face-mask barotrauma (which occurs in descent with failure to equalize pressure in the mask through nasal exhalation) has been reported to induce rupture of incompletely healed corneal or scleral wounds. This kind of severe barotrauma injury is usually associated only with descent in individuals rendered unconscious through a prior diving accident.
If your patient is certified and has prior experience, and takes proper precautions, I think he's OK for recreational diving.
[By a recognized LASIK expert and corneal surgeon, Dr. "S."]: The web site referenced by Dr. Wallace is sketchy and not original. A better reference is the article by Dr. "B." in Survey of Ophthalmology 39:347, 1995. In it, "B." makes dogmatic recommendations about waiting times between corneal surgery and diving (6 months for PK). But, if you carefully read the article and look at the references, you will find that it contains only general references on corneal wound healing and information about the IOP required to rupture various types of wounds (RK, for example). Notably, there seem to be no reports of surgical wound rupture after ocular surgery, nor are there any data to show that IOP increases in divers that fail to equalize their masks. On the contrary, it is noted that there have been no reports of wound problems in Navy and Coast Guard divers after RK. If you critically read the section on diving after corneal surgery (page 357), you will see that the six-month recommendation is totally unsubstantiated by any data or theory.
[by Dr. Wallace]: I appreciate the time and effort you have put into your reply re this topic. It seems that you are displeased with my response, with the "Dining and the Eye" web site, and with the "Dr. B." article directly referenced by the site. Yet when all is said and done, we arrived at exactly the same conclusions and recommendations re the original question.
I, too, was only attempting to lend assistance to another physician asking a legitimate question. Having been a certified diver since my teens, I felt the web site was a good starting point that (a) explained the fundamentals of diving; (b) touched on the critical issues of compressibility of gases and (not) liquids, (c) summarized current literature and thinking re ocular risks appropriately and (d) provided reasonable (if perhaps overly dogmatic) advice that made sense.
It seems to me that the author of the above site was trying to assimilate and coalesce information from widely disparate sources including original research, ophthalmology, general medicine, basic physics, trauma, military experience, and his own expertise gleaned through years of diving. To do so in a handful of web pages in a fashion that makes sense and offers reasonable advice is not so bad, in my opinion.
I appreciate Dr. S's very insightful, if rather critical comments about the "Diving and the Eye" web site referenced in my last correspondence on this topic. I forwarded his comments (and mine) to Dr. "C.", author of the web site. Dr. "C's" comments back to me are copied below:
Dr. "B"" is a personal friend and is quite knowledgeable about all aspects of diving (previous leader of Navy Seal Team 1). His review is very well done and his conclusions about post surgical wait are well thought out and substantiated by good basic work on animals. As you would expect, there are no 'double-blinded, random' human studies on a subject of this nature.
Dr. S seems intent on a debate, but I'm only an observer. Consequently I am referring this to Dr. "B" and hopefully he will respond. I'll keep you in touch as to any more information on the subject.
Best regards for safe diving!
[by Dr. Wallace]: Interestingly, though it seemed that Dr. "S" was keenly critical of the observations and 'dogmatic' recommendations of others, the recommendations made by us all, including his, are consistent and in agreement regarding the relative safety of SCUBA diving in Dr. "T's" patient, 14mos post PKP.
I have tremendous regard for Dr. "S" and his contributions to our profession, as well as to our chat group. I also understand that from a strictly academic and research perspective, his take on this issue may be precise. In a real world context, should a real disagreement ever arise, I'll side with the experienced diver and Seal Team member every time.
[by Dr. "C.", author of the "Diving and the Eye" website]: Hello Dr. "S."
Thanks for visiting our web site! I appreciate your insightful comments and observations, particularly the one about the 'constipated Valsalva maneuver'. Prophylactic Metamucil would seem to be in order for post op eye surgery.
I'm a retired general surgeon and other than being an avid diver with considerable training in diving medicine I can offer very little in the way of rebuttal to your observations. My section on the Eye in Diving is essentially a compilation for the non-medical diver and the non-diving medical professional. It does not profess to be a learned original medical treatise but is attempting to carry a message to the many divers and doctors who don't seem to have access to any diving medical information. My role is somewhat that of a messenger; the material published on the web site is factual to the extent that it all has been published or presented by authorities on each subject.
With that background in mind, I have referred your letter to Dr. "B." (also Captain, US Navy) who is an Ophthalmologist/Navy Seal (Diver) for his comments. Here is his response:
[by Dr. "B"]: Got your e-mail today. I am heading out to Tampa for a workshop on the Tactical Management of Urban Warfare Casualties and do not have time to answer this issue as well as I would like, but I do need to make a few quick observations.
1. Dr. "S." is indeed a nationally recognized leader in the field of cornea surgery. In fact, one of the two cornea specialists that I had review the proposed guidelines for minimum convalescent periods after surgical procedures trained under Dr. S and speaks very highly of him.
2. I'm not sure what Dr. "S." means by "dogmatic." The recommended convalescent periods before diving are just that. They are certainly not based on prospective, double-blinded, and randomized trials of diving exposures on post-operative patients. Institutional review boards tend to frown on that sort of thing. They are based on a combination of the available literature on wound healing and clinical experience. The proposed guidelines were reviewed by cornea specialists (2) and retina specialists (2) prior to being published and their recommended changes incorporated. Dr. S. (or anyone else, for that matter) would be welcome to publish their own recommendations on this issue. It would be most illuminating to generate a dialog on this topic in the literature.
3. The discussion on IOP in the messages is misleading. As you remember from the diving physics talk in Little Cayman, the normal IOP measurement is a "gauge" pressure rather than an absolute pressure. Thus, an IOP of 15 as measured in the clinic reflects an absolute pressure of 15 + 760 or 775mmHg. At 66 feet, the intraocular pressure in this eye (and the rest of the body tissues) would be 1535 mmHg. As long as there is not a facemask with its accompanying air space in front of the eye - there is no trans-corneal pressure differential and no problem. Likewise, if a facemask is in place, but the air space pressure is equalized - no problem. If, however, the facemask is not equalized, the relative vacuum inside the mask could theoretically be as high as 1535-760 or 775 mmHg. The pressure required to rupture at least one corneal incision in post-RK human cadaver eyes is approximately 215mmHg (reference cited in the Survey article). This is a study that I doubt will be repeated on living eyes.
Hope this helps,
[by Dr. Wallace]: Thank you ever so much for forwarding all our comments to Dr. "B.", and for forwarding his reply. I believe this has elevated the level of understanding, and level of interest, in diving issues as they affect the eye by our online group.
The group consists of at least several hundred ophthalmologists worldwide, all of whom specialize in or are interested in corneal disease, surgery, and related topics of anterior segment surgery, cataract, uveitis, and external (ocular) disease. As such, it is sometimes a little self-absorbed. I think it is fantastic that we can get world-class input, literally, 'from the horse's mouth' within hours of discovering your web site. I am also pleased that Dr. B's comments were able to clarify for the group some misconceptions.
One of the reasons the forum is so popular, to be honest, is that the new methods of laser vision correction (PRK for photo-refractive keratectomy and LASIK for laser-assisted surgical in-situ keratomileusis) have become so popular. This forum is used by participants to address issues of problem-solving, troubleshooting, case analysis, and current thinking about evolving technology. These new methods of vision correction are extraordinarily promising, with far greater stability, predictability, and accuracy of correction than with any prior incisional technique including radial keratotomy.
[by Dr. "S."]
Guess my post stimulated a feisty discussion (which was the intent), and I certainly appreciate the inciteful responses from Dr. "C." and Dr. "B." My comments were actually stimulated by Dr. Wallace's statement that, "The website referenced does state that face-mask barotrauma (which occurs in descent with failure to equalize pressure in the mask through nasal exhalation) has been reported to induce rupture of incompletely healed corneal or scleral
wounds," because I have sought and never been able to find such reports in the literature. I still do not know of such a report.
It sounds as if the only issue for further discussion is the one regarding mask barotrauma.
Dr. 's theoretical calculation of the differential pressure change is only applicable to an enclosed vessel with a rigid wall and is not appropriate for the eye.
A basic principle of physics is that unbalanced force on an object will produce movement until the forces are again equalized. If the pressure differential between the inside of the eye and the outside of the eye increases, something
must happen to equalize forces on the eye wall again. This occurs by two mechanisms (excluding aqueous dynamics): expansion of the eye and an increase in tension on the eye wall.
At sea level, the IOP is about 15 mm Hg higher than atmospheric pressure (about 760 mm Hg), and this IOP is balanced by the tension of the sclera/cornea. During descent with an unequalized mask, the mask pressure remains at roughly 760 mmHg, while the pressure in the body increases by about one atmosphere per 33 feet (in addition to the 760 mmHg at the surface) to about 2280 mmHg. If the cornea and sclera were configured exactly as they were at the start of the dive, then the pressure differential across them would be 2280 - 760 + 15 = 1535 mm Hg. (Dr. B., I get a different number than you did. Correct me if I am wrong, but I think you neglected to add sea level pressure to the absolute pressure within the eye when you did your calculation.)
The problem with this calculation and that of Dr. B. is that it assumes rigidity of the eye wall. In fact, the eye expands during descent without mask clearing until forces on the wall of the eye are again balanced. For noncompressible fluids (like aqueous/vitreous), minimal expansion (permitted by the elasticity of the cornea/sclera) causes a rapid decline in the pressure differential across the eye wall. This translates to a relatively small increase in cornea/scleral tension, which is the force leading to wound separation. Furthermore, changes in aqueous production and drainage can help to restore normal IOP differential.
The difference between the behavior of the fluid-filled normal eye and the vitrectomized eye containing gas is the relationship between volume and pressure of the intraocular contents. Descent to 66 ft without mask clearing in an air-filled, vitrectomized eye would require the eye to triple in volume to make the absolute pressure in the eye equal that in the mask. Clearly, the sclera is not sufficiently elastic for this to happen without an increase in tension sufficient to rupture almost any wound.
As far as I know, nobody has ever measured IOP during mask squeeze. (It would be an interesting project that could be carried out in a decompression chamber with an appropriate apparatus simulating a mask.) However, common sense would suggest that extremely high IOP's must not be reached in real world situations--even with failure of mask equalization. If Dr. "B." were correct in calculating an increase in IOP (differential) during mask squeeze at a rate of 760 mmHg per 33 feet of water, then we should see an increase of 185 mmHg to 200 mmHg IOP differential if a diver descended to only 8 feet without equalizing his/her mask (33ft/760mmHg = X/185mmHg, where X = depth of dive). If this actually happened, one would think that beginning divers would experience pain, nausea, and vomiting like patients who experience an increase in IOP to only 50-60 mmHg after surgery or during angle closure glaucoma.
If IOP's really reach 775 mmHg as Dr. B. calculates or 1535 mmHg as I calculate at 66 ft with mask squeeze, why have we not seen RK wound rupture, even 6 or more months postoperatively in divers? Note that the 215 mmHg level cited as the rupture pressure by Dr. B. should be reached at just below 8 feet!
Dr. Wallace, I am not "displeased" with your answer or Dr. C's web site except to the extent that they may contain misinformation with regard to wound rupture and diving. And I certainly don't question your intention to lend
assistance to another physician asking a legitimate question. As physicians, scientists, and academicians, it is important for us to validate information before we "pass it on" to our colleagues/trainees in the form of papers, review articles, web sites, lectures, and even e-mail. So, if there are wound ruptures from diving out there, let's hear about them - and both of us can learn something. If we can find no evidence that they occur, let's stop saying that they do. I agree that we can make educated guesses about appropriate waiting times after surgery, but they should be labeled as such (as Dr. B. does in his excellent Survey review), and we should recognize that others may reach different conclusions.
I think we all learn more from a little skepticism and healthy discussion.
By the way, there is an excellent book edited by Richard H. Strauss, MD., titled Diving Medicine, (not referenced in Dr. B.'s article). It is 420 pages in length and was originally published in 1976 by Grune and Stratton. I am not sure it is still in print, but it contains a wealth of information including case histories, specialized diving tables, accident investigation techniques, etc.
[by Dr. Wallace]:
I thank Dr. C. for the correction to my prior posting, generated in the wee hours. Dr. C., a general surgeon, is the author of the "Diving and the Eye" web site, and Dr. B. is a board-certified ophthalmologist who wrote the "Survey" article. The previous postings by me, Dr. S., Dr. B. and others re face-mask barotrauma failed to include three other contributing factors that might blunt the effect of face-mask barotrauma on the eye:
1. Persons rendered unconscious can still breathe. In an underwater setting, loss of consciousness per se may not be fatal if the regulator mouthpiece is retained. If retained, during descent any additional inspiratory effort (great enough to open the low-pressure stage of a 2-stage regulator) might afford at least partial equalization, assuming no air blockage between mouth and nose.
2. Venous stasis in the facial tissues inside the mask seal: If intra-mask negative pressure is greater than venous return negative pressure, venous pooling can occur. I have no idea how significant this may or may not be, relative to the overall volumes under consideration.
3. Third-spacing. Third spacing is the accumulation of fluid within body tissues or cavities but outside the vascular system. Eyelid and subconjunctival hemorrhages would be considered a subset of this category, I think. The time-lag to develop third-space non-hemorrhagic fluid accumulation would be expected to be slow relative to rates of pressure
change in a mask during uncontrolled descent, so overall I do not think this contribution would affect the acute situation significantly. At least the topic of third spacing will be less foreign to Dr. C., as a general surgeon, than to the ophthalmologists participating in this dialogue.
[by Dr. "B."]
A few more comments on the facemask barotrauma discussion:
1. Let me go over the pressure issue once more. At 66 FSW, the absolute pressure on the body IS 2280 mmHg. Nothing theoretical about that figure. Dr. S. - you did in fact catch me forgetting to add the 760 mmHg of pressure at the surface to this figure. I corrected this mistake in an earlier e-mail. The THEORETICAL relative negative pressure that could be generated in the air space of the facemask is then 2280-760 or 1520 mmHg. This magnitude of pressure
differential is probably rarely, if ever, achieved, primarily because divers instinctively add air to their masks as they breathe. In addition, one would expect distention of both the mask and the periocular tissues to partially collapse the air space and partially compensate for the pressure differential. In my experience, a negative pressure in the mask does not cause water to leak in.
2. What is the ACTUAL maximum negative pressure achieved in the air space of a facemask once these factors are considered? I don't know, but I can provide some observations:
- I am unaware of any published reports of RK or PKP incisions rupturing as a result of facemask barotrauma and I've looked pretty hard.
- I have heard of two anecdotal, unpublished reports of endophthalmitis occurring after diving in eyes with recent RK. This information was a post-lecture comment at one of the Medical Seminar diving meetings and I unfortunately don't remember the name of the physician who made the comment. It's worth remembering, however, that we have to consider the possibility of sea water gaining access to the eye through non-healed incisions. Again - no data but something to consider.
- I know of two anecdotal, unpublished reports of divers who had hyphemas as a result of facemask barotrauma. My partner here in Pensacola treated these patients. Both were native breathhold divers in the Philippines who became unconscious and sank 20-30 feet in the water column before being rescued.
3. Doctor Wallace - you asked about refractive surgery in the Navy. I'm happy to say that the current PRK initiative is one that I started in 1992 in my capacity as Biomedical Research Director for the Navy SEALs. The results obtained by Steve Schallhorn at the Naval Medical Center in San Diego were excellent, and the Navy has now (for the first time ever) approved this procedure for SEALs, divers, and everybody else. The SEALs have been extremely happy with this procedure and are having it done as fast as we can get them in there. The Air Force is studying it as we speak (or type, I guess) and the Army is, well, the Army. Don't know when they'll come around. The question now is - do we want to look at LASIK for the SEAL community or should we wait a few more years until the surgery has developed a bit more. I would be most interested in your thoughts and those of Dr. S. on this issue, since this project will be discussed in Tampa on Friday by the US Special Operations Command Biomedical Initiatives Steering Committee as a candidate for FY00 funding.
The above is not intended to be a complete discussion of all risks associated with either SCUBA diving or laser refractive surgery in association with diving. We hope you at least find the information valuable and worthy in a real-world context to you.