Applications for corneal stromal allografts continue to grow
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Small incision lenticule extraction has been used in more than 3.5 million refractive surgery procedures globally, primarily for the treatment of myopia and astigmatism.
Developed by Carl Zeiss Meditec of Jena, Germany, SMILE was approved by the FDA in 2016 for the treatment of –1 D to –10 D of myopia with 0.75 D to 3 D of astigmatism. The procedure requires a very precise femtosecond laser, exemplified by the Zeiss VisuMax laser, and a skilled surgeon. More than 600 articles have been published in the peer-reviewed literature supporting the safety and efficacy of SMILE.
A side benefit of SMILE is the living donor lenticule that is removed to induce the refractive change. Innovative and pioneering surgeons have developed many uses for this pristine lenticule removed from a healthy human patient who chooses to donate it to benefit others. The lenticule can be stored short term in standard corneal preservation media such as Optisol GS (Bausch + Lomb) or simply placed in any sterile container in balanced salt solution. Lenticules can also be processed for long-term preservation in anhydrous glycerol at –78°C, freeze dried and even cross-linked for enhanced tissue stability. Cross-linked sterile corneal stromal lenticules are also prepared by some eye banks, including the widely used CorneaGen VisionGraft.
The applications for corneal stromal allografts are many and growing. Glaucoma surgeons use corneal stromal tissue to reduce erosion in tube shunts and to treat complications of trabeculectomy. Corneal surgeons use corneal stromal allografts for therapeutic applications in tectonic grafts. Now, refractive surgeons are joining in with a host of refractive indications. Near the top of the list are several potential applications for enhancing refractive outcomes in keratoconus. These include tissue addition procedures across the visual axis that thicken, strengthen and regularize the cornea, exemplified by stromal lenticule addition keratoplasty and the use of properly sized human lenticules as an alternative to the PMMA Intacs (CorneaGen) in corneal tissue addition for keratoconus. Early results are promising, and many of the pioneering surgeons are quoted in the accompanying cover story. Tissue addition procedures can also be used to correct presbyopia, hyperopia and hyperopic astigmatism.
These new procedures are bringing refractive surgery to keratoplasty. Every patient, even those with a diseased or dystrophic cornea, desires the best possible best corrected visual acuity — and the best possible uncorrected visual acuity. To the well-established refractive corneal surgery and refractive cataract surgery, we are now adding refractive keratoplasty and refractive cross-linking. Waiting in the wings are refractive scleroplasty for presbyopia and progressive myopia and perhaps even refractive retinal/vitreous surgery. One could argue that nearly every ocular surgery has a potential impact on the patient’s refraction, either positive or negative, and surgeons and companies worldwide are focusing their energy on not only preserving and restoring vision, but also enhancing it through the application of refractive surgery.
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