Precise cuts with FS laser

Stronger wounds and faster healing improve refractive outcomes

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As with many ophthalmic procedures, restoring vision is no longer enough for penetrating keratoplasty. “Patients want to know how quickly they will get back to their life, what is the rate of their visual recovery, are they going to be limited to wearing rigid gas permeable lenses… Refractive goals really are our current challenges,” Marjan Farid MD told the American Academy of Ophthalmology 2017 Annual Meeting in New Orleans, USA. Femtosecond lasers help, said Dr Farid, of the University of California – Irvine, USA. Lasers enable precise cuts at specified depths that cannot be done manually. The resulting interlocking incisions have been shown to be stronger, and promote faster wound healing and earlier suture removal. They may also improve refractive outcome, though more study is needed to confirm this, she added. The medical and biomechanical characteristics of femtosecond PK incisions vary with profile. For example, a “top hat” profile provides a broad expanse of donor endothelium, but is not self-sealing due to aqueous leaking in dislodging the posterior flap. A “mushroom” profile features a broader anterior surface and preserves more host endothelium, making it attractive for keratoconus patients, but does not inherently align the anterior surface or hermetically seal. Inspired by self-sealing cataract incisions and developed by the late Roger Steinert MD, the “zig-zag” profile provides a smooth transition between host and donor tissue, while its interlocking pattern creates a precise apposition over 360 degrees. Its structure also guides suture placement, making it easier to use, Dr Farid said. Early lab tests show zig-zag PK grafts have higher burst strength than conventional incisions (Steinert et al., Am J Ophthal 2007; Maier et al. Cornea 2016; Malta et al. Curr Eye Res 2009; Bahar et al. Cornea 2008), Dr Farid noted. “Several studies have clinically shown patients who have had femtosecond laser cuts can have sutures removed at an earlier timepoint,” she added (Chamberlain et al. Ophthal 2011; Bahar et al. BJO 2009; Birnbaum et al. Graefes Arch Clin Exp Ophthal 2013; Shivanna et al. Indian J Ophthal 2013). Easier and lower-tension suturing enabled by zig-zag incisions also reduce torsional tension and vertical misalignment, Dr Farid said. Ongoing retrospective studies at UC Irvine suggest this reduces astigmatism and HOAs. The resulting more-regular astigmatism is easier to correct with LASIK or toric IOLs, leading to even better refractive outcomes. However, other studies are less conclusive regarding refractive benefits, Dr Farid noted. Standardised, prospective head-to-head studies comparing incision patterns and similar graft size are needed to quantify any differences. Nonetheless, she believes femtosecond laser incisions are superior. “If you had to have PKP, what incision would you prefer? Femto is the future.” Marjan Farid: mfarid@uci.edu