With LASIK still the most popular form of refractive surgery, it behooves refractive surgeons to keep updated on potential complications, even those that remain quite rare. Those involved with performing this type of surgery must understand the risk factors, prevention, early diagnosis, and treatment of LASIK complications. Keratoectasia, although quite uncommon, is a serious complication that has severe implications for the patient's vision (Figure 1).PREOPERATIVE SCREENING
I divide ectasia into the preoperative risk factors for developing it. Screening patients preoperatively for their susceptibility to ectasia involves a careful examination for evidential markers.
First, I examine the stability of the patient's refraction. Someone who presents with a refraction or keratometry that has changed significantly needs his refractive stability evaluated over several months. If he is in his early 20s, he may be a premature keratoconus patient. One should be concerned about contact-lens or spectacle intolerance due to unstable refractions as well as a BCVA of less than 20/20 if no ophthalmic pathology is evident.Suspicious Medical History
A history of atopic dermatitis or chronic conjunctivitis, although not necessarily a risk factor for ectasia after LASIK, is reason enough to further work up a patient before considering treating him with refractive surgery. Chronic eye rubbing also denotes a poor refractive surgery candidate.
Type of Refraction
Work performed by Doyle Stulting, MD, and others showed that ectasia is extremely rare in low myopia.1 Among risk factors they identified for developing ectasia were refractions greater than -8.50D, a residual stromal bed, and evidence of forme fruste keratoconus.
PREOPERATIVE CORNEAL MAPPING AND PACHYMETRY
All the aforementioned conditions require further investigation. I would not necessarily rule out performing LASIK in these patients, but I would proceed cautiously. I will not perform LASIK on a patient who cannot stop rubbing his eyes. Likewise, I reject LASIK for those whose preoperative mean keratometry is above 47.20D or whose central corneal pachymetry is less than 500µm, regardless of their prescription in either case. I will instead recommend surface ablation to those patients. I have been performing more surface ablation in recent years, because I have become less tolerant of the potential risks of LASIK (Figures 2 and 3). Furthermore, I do not feel that new technology, such as the Intralase FS laser (Intralase Corp., Irvine, CA) has sufficiently alleviated those risks to make me more comfortable performing LASIK than surface ablation.
I use keratometry and topography to rule out any suspicion of forme fruste keratoconus. A difference in inferior and superior steepening of more than 1.50D might indicate an irregular cornea. If I see topographic or keratometric evidence of irregular astigmatism, or if I cannot correct the patient to 20/20 despite a normal preoperative examination, then I will choose surface ablation.INTRAOPERATIVE PRECAUTIONS
The most important thing for the refractive surgeon to know is the parameters of his devices. I am extremely nervous when asked to try a new microkeratome, because I do not know how it will cut in my hands. It behooves each surgeon to measure and keep track of the thickness of the flap in every LASIK case. I use the Moria 1 disposable microkeratome unit (Moria, Antony, France), with which I produce flaps from 90- to 135µm. I always use the thickest flap I have ever created as a basis for calculating a patient's ablation depth and amount of residual stroma. I will plan to leave 300µm in the stromal bed after laser application as opposed to the FDA's recommended 250µm for a primary LASIK procedure.
To calculate the residual stromal bed, I measure the stromal depth before ablating it and then postoperatively subtract the amount that the laser indicates it has removed from the central cornea. Subtraction technology is currently the best way to measure flap thickness, although a more direct method would be preferrable. I make sure to include these data in the patient's chart so that, if he returns for an enhancement, I know the postoperatively calculated stromal bed.
Also on the subject of enhancements, surgeons must review any available surgical notes preoperatively so that they know the original ophthalmologist's intent. When it is time to relift the corneal flap to perform the enhancement, the surgeon needs to know (1) how much tissue is available and (2) how much he is going to remove in order to calculate the residual stromal bed. For example, if 350µm of tissue is available after measuring under the flap, calculating the ablation for 120µm will certainly leave less stromal tissue than the FDA's recommendation of 250µm, and the surgeon will have to abort the procedure. Aborting a procedure is a difficult chore for a surgeon, but preoperative planning can avoid it. If planning reveals that the flap is thicker than anticipated, then the surgeon's best option is to put the flap back down. The literature supports laser surface ablation treatments on the flap itself for such patients at a later date,2 which is an important option to remember.TREATING ECTASIA AFTER LASIK
Diagnosing ectasia after LASIK is critical, because these patients tend to have wonderful early postoperative results and only schedule a return visit when they have problems. One hopes that they will see their operating surgeon, because he has all their data. My staff and I strongly encourage our patients to return to us if they experience a postoperative problem. We tell them that their data are important to us. We always take postoperative topographic measurements with an Orbscan topographer (Bausch & Lomb, Rochester, NY) at 1 month and measure the pachymetry at 3 months. We record both of these calculations in the patient's chart. If we see myopia developing, we follow it for 1 to 2 months while taking serial topographies and refractions to make sure the refraction is stable. I become very suspicious if the patient's BCVA is less than it was in the preoperative or early postoperative period. A patient who becomes myopic, who develops some astigmatism, and whose BCVA drops to 20/30 is a big concern.
Making the diagnosis is important because it is very tempting to automatically enhance an eye. In following such an individual, I use the Orbscan topographer and examine the posterior float, which I use as a tie-breaker rather than an absolute determination. I rely on other clinical and historical findings to give the diagnosis much more weight than an abnormally elevated posterior float from the patient's Orbscan.
Once I have diagnosed ectasia, I inform the patient and advise him about his treatment options. I explain that my goal is to improve his BCVA. This is a critical time for the operating surgeon, who has earned the trust of and developed a good rapport with the patient. On the other hand, a surgeon whom the patient has sought for a second opinion must spend time with the patient and deal with his anger, disappointment, and shock at the situation, even if he understood the risks. A patient who has to revert to using contact lenses will almost always resist this treatment, because he underwent refractive surgery to eliminate this dependence. The surgeon must be cognizant, empathetic, and supportive of the patient's duress, but he must also be firm in delivering his advice. I tell the patient that contact lenses are likely his best option, because they have the highest likelihood of improving his visual acuity to a satisfactory level.MANAGING IOP
In my early management of ectasia, in addition to using a contact lens, I will lower the patient's IOP with a beta-blocker (Betimol; Santen Inc., Napa, CA) once or twice per day if the patient tolerates it. If an IOP component is furthering the ectasia, the beta-blocker may retard or limit it. I think this approach is worth a trial early on. This type of beta-blocker usage has had few case reports,3 but it has been impressive in very mild cases of ectasia. Certainly, full-blown keratoectasia will not respond to IOP lowering.
Finally, if the patient cannot tolerate contact lenses, I will explore every possible means of treating the ocular surface to make this modality viable. For patients who simply cannot wear a contact lens, intrastromal corneal ring segments (Intacs; Addition Technology, Inc., Des Plaines, IL) are a very interesting option. I am planning to use them for several patients to treat their ectasia. Although the available literature on Intacs is early, it seems to support their use as a modality for ectasia once contact lenses have failed,4 and I think the approach is definitely worth a try. The only other alternative is corneal transplantation, which is a last resort because of the intraocular nature of the procedure and the long-term immunological and postoperative care those patients need.
Also, I am looking forward to the work of Theo Seiler, MD, PhD, in Dresden, Germany, and Brian Boxer Wachler, MD, in Los Angeles with regard to using corneal collagen crosslinking riboflavin (see Corneal Collagen Crosslinking With Riboflavin). This modality seems very promising in keratoconus and should be quite applicable to ectatic eyes. It may allow us to remedy this thankfully rare but devastating complication.Shachar Tauber, MD, is Director of Refractive Surgery and Ophthalmic Research at St. John's Hospital and Clinic in Springfield, Missouri. He states that he holds no financial interest in the products or companies mentioned herein.
Dr. Tauber may be reached at (417) 820-9723; firstname.lastname@example.org.
1. Stulting D. Risk factors and prognosis for corneal ectasia after LASIK. Ophthalmology. 2003;11:2:267-275.
2. Trattler W. Safety and efficacy of LASEK to enhance previous LASIK. Paper presented at: The ASCRS/ASOA annual meeting; April 28 to May 2; San Diego, CA.
3. Huang X, He X, Tan X. Research of corneal ectasia following laser insitu keratomileusis in rabbits. Yan Ke Xue Bao. 2002;18:2:119-22. Chinese.
4. Siganos CS, Kymionis GD, Astyrakakis N, Pallikaris IG. Management of corneal ectasia after laser in situ keratomileusis with Intacs. J Refract Surg. 2002;18:1:43-46.