Refractive mishaps following corneal procedures typically result in corneal irregularity, opacification, or both. Although corneal irregularity can be treated with a rigid contact lens, opacification requires removal by ablation or grafting. Avoiding these problems is essential, however, as with any surgical procedure it is inevitable to incur a small number of adverse and unexpected complications.IRREGULAR ASTIGMATISM
The causes for irregular astigmatism following LASIK include flap complications such as buttonholes and partial or fragmented flaps. After ablative refractive procedures like LASIK, LASEK (Figure 1A), and PRK, ectasia can arise, causing irregular astigmatism. Ectasia can also occur after incisional refractive surgery such as radial keratotomy (RK) (Figure 1B). Additionally, decentrations and ablations in spite of a partial flap can lead to irregular astigmatism as can inflammation such as diffuse interlamellar keratitis (Sands of the Sahara) and microbialkeratitis. OPACIFICATION
The aforementioned postoperative LASIK flap complications with subsequent scarring (Figure 2) can produce postoperative opacification. Other causes of opacity include postoperative surface ablation haze, scarring, and stromal outgrowth or “sub-epithelial fibrosis” following incisional surgery. As mentioned earlier, inflammation such as diffuse interlamellar keratitis or microbial keratitis can cause corneal scarring. Sporadic cases of atypical mycobacterial keratitis have been reported,1,2 and, because of the nature of this organism, it is frequently diagnosed late, requires prolonged treatment, and often requires flap amputation. These cases result in both opacification and corneal irregularity.MANAGEMENT
The best noninvasive option for managing irregular astigmatism is a rigid contact lens, but it is typically not a favored option in a refractive surgery patient who has electively chosen vision correction. Opacification requires the removal of the opaque tissue, depending on its extent, by way of further ablation or excision and replacement by a grafting technique.
Many surgeons electively use mitomycin C (MMC) to prevent haze. This technique seems to be effective, but there is little scientific evidence demonstrating its long-term safety. MMC 0.02% is effective when used in conjunction with phototherapeutic keratectomy (PTK) for the elimination of superficial scarring. I have used MMC successfully in this context with a total application time of 15 seconds, rather than 2 minutes. Figure 3A shows scarring from an occult buttonhole post-LASIK (UCVA of 20/40, treated by PTK and a 15-second application of MMC). Figure 3B shows an eye 6 months after treatment that achieved 20/15 UCVA.
What options are available in cases of extreme irregularity and deeper opacification or where there is reduced corneal thickness? An alternative that I favor is a homoplastic automated lamellar therapeutic keratoplasty (ALTK). This procedure involves using a microkeratome to remove the anterior cornea and replacing it with a similarly fashioned flap from a donor globe or cornea. Commercially, the Moria ALTK system (Moria, Antony, France) is available specifically for this purpose. I adapted the Automated Corneal Shaper microkeratome (Bausch & Lomb, Rochester, NY) and designed an artificial anterior chamber to enable flap creation from donor corneal discs (Figure 4). The advantage of this technique is I am able to remove the anterior cornea and replace it with a donor of predetermined thickness by changing the thickness plate. This method is useful for removing corneas that have anterior opacification and those with relatively fine irregularities. Figure 5 shows an eye that underwent RK followed by PRK and developed severe scarring. I performed a homoplastic ALTK procedure, and, after the patient achieved refractive stability at 18 months, I performed LASIK to correct the residual refractive error. The eye now has a UCVA of 20/30 and a BSCVA of 20/20.
When a cornea is too thin for a flap resection, a PTK can be performed, and a lamellar flap can be added to the epithelialized surface to prevent further scarring, provide more corneal substrate, and make future ablative refractive surgery possible.ECTASIA
Ectasia remains a problem. It occurs in corneas predisposed to the condition. Corneal refractive surgery is best avoided in corneas with inferior steepening. Additionally, surgeons should maintain a high index of suspicion for thin and steep corneas with a steep posterior float on Orbscan topography (Bausch & Lomb,). Because of variation in flap thickness,3 I advocate measuring the corneal bed's thickness following flap resection and prior to laser ablation in cases of a thicker-than-expected flap. I believe this process should be standard practice. Recently, two cases of ectasia with flaps thicker than 220µm on ultrasound biomicroscopy were referred to me.
Although contact lenses remain the mainstay of treatment, there have been reports4 of using intracorneal rings, either Intacs (Addition Technology, Inc., Des Plaines, IL) or Ferrara rings (Mediphacos Ltd., Belo Horizonte, Brazil) to stabilize and flatten the cornea. The long-term effect of these rings is unknown, but the devices are worthy of consideration prior to corneal grafting. Figure 6 shows an eye after RK with inferior ectasia initially sutured with some early effect. This same patient later benefited from the implantation of a single Intacs ring.
In the long term, collagen crosslinking may play a role in the prevention as well as the treatment of ectasia by strengthening the cornea and averting the progression of the ectatic condition.5
With improved keratomes and the advent of the Intralase FS laser (Intralase Corp., Irvine, CA), the prevalence of refractive surgery disasters will decrease. Luckily, there are a number of options available for the correction of such catastrophes. However, ultimately, many patients may still require a deep lamellar or penetrating keratoplasty.
Sheraz M. Daya, MD, FACP, FACS, FRCS(Ed), is Director and Consultant at the Centre for Sight, Corneoplastic Unit and Eye Bank, the Queen Victoria Hospital in East Grinstead, United Kingdom. He states that he does not hold a financial interest in any product or company mentioned herein but is occasionally reimbursed for travel expenses by Bausch & Lomb. Dr. Daya may be reached at +44 1342 321 201; email@example.com. Freitas D, Alvarenga L, Sampaio J, et al. An outbreak of Mycobacterium chelonae infection after LASIK. Ophthalmology. 2003;110:276-285.
2. Fulcher SF, Fader RC, Rosa RH Jr, Holmes GP. Delayed-onset mycobacterial keratitis after LASIK. Cornea. 2002;21:546-554.
3. Giledi O, Mulhern MG, Espinosa MM, et al. Reproducibility of LASIK flap thickness using the Hansatome microkeratome. J Cataract Refract Surg. 2004;30:1031-1037.
4. Colin J, Cochener B, Savary G, Malet F. Correcting keratoconus with intracorneal rings. J Cataract Refract Surg. 2000;26:1117-1122.
5. Wollensak G, Spoerl E, Seiler T. Riboflavin/ultraviolet-a-induced collagen crosslinking for the treatment of keratoconus. Am J Ophthalmol. 2003;135:620-627.