FACT: The LASIK Flap is Sturdy, and Would Require Extreme Force to Dislodge It
Since its approval by the U.S. Food and Drug Administration in 1998, LASIK has been performed on an estimated 30 million eyes worldwide. The procedure is utilized by the United States armed forces to improve readiness of active duty soldiers, and many professional athletes have enjoyed its benefits as well. One common concern amongst the general public, however, is the possibility of the LASIK flap becoming dislodged or dislocated.
While extremely uncommon, flap dislocations occur more frequently in the early postoperative period (the first few days) than later. In fact, flap dislocations more than 1 year following surgery are extraordinarily uncommon. Early flap dislocations are generally caused by eye rubbing in the first several days after surgery. LASIK patients are counseled not to rub their eyes for several weeks after surgery, and most patients are advised to sleep in protective goggles for up to the first postoperative week. Late flap dislocations are always associated with ocular trauma, though most ocular trauma does not cause a dislocation, thus accounting for their significantly reduced frequency compared to early dislocations.
The LASIK flap actually consists of two wounds: (1) the planar interface between the flap and the underlying corneal stroma and (2) the circumferential, vertical (or near-vertical) edge of the flap. Laboratory and animal studies have demonstrated that the tensile strength of the edge of the flap is approximately 28% of that of the normal corneal stroma while the flap interface is less than 5%. This is not surprising because the cornea does not have blood vessels and, thus, wound healing following cornea stromal incisions is significantly weaker than vascularized tissues (eg skin). LASIK surgeons actually take advantage of this reduced tensile-strength wound healing; in the unlikely scenario in which additional laser treatment may be necessary, LASIK flaps can usually be re-lifted months or even years following the original surgery. So, it is well documented that the tensile strength of the LASIK flap is less than that of unoperated corneal tissue.
LASIK flaps were initially created using mechanical microkeratomes. Starting in the early 2000s, femtosecond lasers were introduced to create LASIK flaps; today, nearly 75% of LASIK procedures are performed using these lasers. Notably, a study comparing microkeratome-created and femtosecond-laser created flaps showed that the incidence of early flap dislocations in the laser group was significantly less than that in the microkeratome group. It is believed that the architecture of the flap edge created by the laser results in a more secure wound compared to those created by the microkeratome. The incidence of flap dislocations was extraordinarily low (2.5%) even in the microkeratome group. Additionally, these studies were performed using early generation microkeratomes and femtosecond lasers; modern microkeratomes and femtosecond lasers are believed to produce even more stable flaps. While no study to date has documented the incidence of late (more than 1 year) postoperative flap dislocations, it is well accepted that this is extraordinarily uncommon and always associated with ocular trauma. These traumatic events fall into two main categories: (1) significant blunt trauma to the eye in which the flap can be dislodged or, in some cases, lacerated and (2) tangential forces (eg, fingernail or pet claw scratching of the cornea) that disrupt the flap edge and secondarily dislodge the flap. In the former group, frequently the severity of the trauma is significant enough to cause other serious eye injury.
In conclusion, it is recognized that LASIK flaps can be dislodged and that this is more of a risk in the very early postoperative phase before healing of the flap wound has occurred. Even so, dislocations early after surgery using modern flap-creation technologies are uncommon, likely far less than 1% of cases. With proper patient education regarding eye rubbing and protective goggles, the incidence of early dislocations becomes extremely uncommon (probably less than 1/1000 procedures). Even though LASIK flap wound strengths are significantly less than that of unoperated corneal tissue, late flap dislocations are decidedly rare and can only occur with trauma; in many cases, these traumatic events produce other eye injuries much more severe than the dislodged flap. So, are LASIK flaps “fragile”? The answer is decidedly “NO”, particularly with modern flap-creation technologies and common-sense postoperative patient precautions. And the proof is in the LASIK pudding: the most avid recipients of LASIK are active individuals, (eg athletes, military, law enforcement, etc) who are exposed to higher trauma risks than the general population. There is even a celebrated case of a US Navy fighter pilot who had LASIK and had to eject from his aircraft; his LASIK flaps remained completely intact in spite of the severe forces he underwent during ejection. Additionally, it is well accepted that the vast majority of dislodged LASIK flaps can be successfully repositioned without causing permanent vision changes. With proper postoperative precautions, flap dislocation should not be a valid concern for individuals considering having LASIK unless they have a reasonable expectation of regular, repeated trauma; for example, mixed martial arts (MMA) fighters may be better suited to PRK or ICL refractive surgery.
Title: Effect of Altitude on LASIK
Authors: Jason W Dimmig MD, Geoff Tabin MD
Précis: The authors report the effects of high altitudes on a group of individuals who had previously had laser in-situ keratomileusis (LASIK) during their multi-day ascent to Mt. Everest (above 26,000 feet). Pre-ascent uncorrected visual acuities were 20/20 in all of the 12 subject eyes at sea level. The patients were then assessed at base camp of 17,600 foot altitude. While visions in all subjects remained unchanged at the 17,600 foot base camp evaluations, 2 of the climbers reported mild visual fluctuation starting at about 26, 400 feet; these resolved by the time they returned to the base camp. Three of the climbers had no reported vision changes even up to the summit at 29,000 feet. The authors noted that these mild vision fluctuations did not interfere with the climbers’ activities. They also observed that this post-LASIK fluctuation in selected subjects at ultra-high altitudes was very different from the uniform hyperopic shift that had been previously reported in post-radial keratotomy (RK) patients who ascended to high altitudes (above 10,00 feet) for prolonged periods. Additionally, the authors noted that individuals who had not had any prior refractive surgery had reported similar vision changes at these ultra-high altitudes and they attributed this to the very extreme hypoxia. The authors concluded that LASIK appeared to be a good and safe refractive surgical option for individuals exposed to high altitudes, certainly superior to RK and probably a better option than spectacles or contact lenses in these scenarios, but those ascending above 26,400 feet should be aware of the possibility of visual fluctuation.
Full reference: Dimmig JW1, Tabin G: The ascent of Mount Everest following laser in situ keratomileusis. J Refract Surg. 2003 Jan-Feb;19(1):48-51
Keywords: LASIK, Laser In-Situ Keratomileusis , Altitude, Hypoxia
Title: Refractive Surgery to Improve Readiness
Authors: Diane Angelucci, Contributing Writer for Refractive Surgery Outlook, interviewing Capt. Elizabeth Hofmeister, MD, MC, USN, and Françoise Froussart-Maille, MD, MSc
Précis: In this American Academy of Ophthalmology Clinical Update, US military surgeon state that “For us, refractive surgery is not a casual procedure, not a cosmetic procedure. It is critical to our operational safety and all the work that we do to try to improve the readiness of our service members.”
In 2015 alone, collectively the US military branches performed 37,000+ refractive surgery procedures, Authors state that refractive surgery offers significant safety advantages, while delivering exceptionally sharp vision. Specifically noted in this article is that “…flaps have remained in place after a pilot’s ejection from aircraft or blast injuries to the eye.” Additionally noted are the few flap dislocations which “… resulted from noncombat accidents, as when patients tripped and poked themselves in the eye.”
Keywords: LASIK Flap Stability,
Title: Extreme LASIK Flap Stability
Authors: Christopher J Richmond MD, Patrick D Barker MD, Edgar M Levine MD, and Elizabeth M Hofmeister MD
Précis: A 28-year-old male F/A-18F Super Hornet naval flight officer ejected from an aircraft at 13 000 feet at a speed in excess of 400 miles per hour 7 years after LASIK. His LASIK flap was unharmed, and vision the next day was 20/15.
Full reference: MD CJR, MD PDB, MD EML, MD EMH. Laser in situ keratomileusis flap stability in an aviator following aircraft ejection. Journal of Cartaract & Refractive Surgery. 2016;42(11):1681–1683. doi:10.1016/j.jcrs.2016.10.001.
Keywords: LASIK, Safety, Flap Stability