BLOG: PK is now a ‘last-resort procedure’ for keratoconus
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Corneal transplantation for keratoconus has traditionally been performed as a full-thickness penetrating keratoplasty and generally is a very successful procedure.
Practitioners certainly shouldn’t hesitate to refer a patient in need of a PK, but today it should be considered a last-resort procedure, rather than a first-line treatment for keratoconus. The availability of corneal cross-linking, better contact lens options and new surgical techniques have significantly changed the landscape for keratoconus management and have reduced the need for PK.
Corneal cross-linking
CXL slows or halts the progression of keratoconus, significantly reducing the need for a PK, especially when the disease is arrested early, preserving vision and corneal stability at the milder stages. CXL with the FDA-approved iLink system (Glaukos) results in a significant lifetime savings of nearly $44,000 per patient, due in large part to fewer PK surgeries (Lindstrom RL, et al).
Keratoconus and other forms of ectasia were once the leading indication for corneal transplant but have dropped to the sixth most common indication since the approval of iLink CXL in the U.S. (Lindstrom RL, et al). This mirrors what has been seen outside the U.S., where CXL has been available for a longer period of time. National registry data in the Netherlands, for example, demonstrated an approximately 25% reduction in corneal transplantation in the 3 years following the introduction of CXL compared with the 3 years preceding it (Godefrooij DA, et al).
Specialty contact lenses
Another factor in the reduction in PK procedures for keratoconus is an increase in specialty contact lens options to manage advanced disease. One study found that among patients with severe keratoconus who were referred for corneal transplantation, 78% could have their vision successfully managed with scleral lenses and avoid keratoplasty even at the later stages of the disease (Koppen C, et al).
While scleral lenses won’t slow or halt keratoconus progression, the technology has become so advanced that it is extremely rare in our clinic that a patient would need a corneal transplant because of the curvature of their cornea being too steep.
For patients with severe keratoconus who have aberrations that affect the quality of vision, we can create custom wavefront-guided optics (Ovitz) to further improve vision. The addition of these optics may be able to improve vision to a point where corneal transplantation is no longer necessary. Currently, our most common indication for corneal transplant is corneal scarring in the visual axis, which does not improve with specialty lenses.
Complications with PK
These are all important treatment advances because, as successful as PK is, the procedure can add challenges to the keratoconus patient journey. Complications, intraoperatively and postoperatively, may occur. The graft may undergo rejection or failure. After each transplantation, patients face long-term topical steroid use, which has its own complications such as secondary glaucoma and cataract formation. There is a lifetime of elevated risk of traumatic dehiscence of the graft. Young patients who undergo one corneal transplant may need a repeat graft later in life.
Therefore, with modern keratoconus management, PK should be reserved for patients who cannot achieve functional vision in contact lenses, including scleral lenses for the advanced keratoconus population, and other surgical procedures carrying less risk, such as intracorneal ring segments or topography-guided excimer laser procedures.
Specialty contact lenses should always be tried, without prejudging whether the patient’s vision can be improved with them or whether the patient could be comfortable wearing or caring for them. The best scenario is that we halt keratoconus progression with CXL, manage vision after that in specialty contact lenses and/or with other surgical procedures and avoid a transplant altogether.
Surgical options
When a transplant is necessary, there recently have been some significant innovations. Deep anterior lamellar keratoplasty (DALK) utilizing the “big bubble” technique is a procedure in which the surgeon removes the corneal stroma all the way down to Descemet’s membrane (DM), preserving the still-healthy DM and endothelium (Trimarchi F, et al). Compared with PK, DALK reduces the chance of immunological rejection.
The adoption of DALK has been slow, however, likely because it is technically challenging. New approaches to anterior lamellar keratoplasty, including the “grip-and-rip” and “groove-and-peel” techniques, have the potential to make DALK simpler to perform. Unlike big bubble, these techniques leave a thin residual stromal bed, which may provide greater protection against intraoperative perforation and possibly more postoperative globe integrity when compared with DALK by big bubble or PK. However, remaining stroma, especially a thick layer of stroma, may lead to interface irregularities which could limit the final postoperative visual result.
There has also been work in the area of intrastromal lamellar keratoplasty, such as Bowman’s layer transplant, intrastromal lenticules, femtosecond laser-assisted stromal lenticule addition keratoplasty and the use of intrastromal tissue ring segments such as corneal allogenic intrastromal ring segment.
Over several years, our group has developed a novel lamellar keratoplasty procedure, corneal tissue addition keratoplasty, in which gamma-radiated allogenic corneal tissue (CorneaGen) is custom-shaped by a femtosecond laser (Ziemer) to create a custom intrastromal inlay. The tissue inlay functions as a lamellar addition of corneal stroma to change the corneal geometry and structure, which can improve visual acuity (Greenstein SA, et al). It is important to note that CXL remains necessary to halt keratoconus progression.
Keratoconus can be a devastating disease, and corneal transplantation remains a key surgical tool to improve patients’ vision. But thanks to CXL, specialty lenses and new surgical techniques, many more patients can achieve excellent visual outcomes with less risk.
References:
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Godefrooij DA, et al. Acta Ophthalmol. 2016;doi:10.1111/aos.13095.
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Greenstein SA, et al. J Cataract Refract Surg. 2023;doi:10.1097/j.jcrs.0000000000001187.
- Koppen C, et al. Am J Ophthalmol. 2018;doi:10.1016/j.ajo.2017.10.022.
- Lindstrom RL, et al. J Med Econ. 2021;doi:10.1080/13696998.2020.1851556.
- Trimarchi F, et al. Ophthalmologica. 2001;doi:10.1159/000050894.
For more information:
John D. Gelles, OD, FIAO, FCLSA, FSLS, is director of the specialty contact lens division at the Cornea and Laser Eye Institute in Teaneck, New Jersey. He also is a clinical assistant professor at Rutgers New Jersey Medical School and an adjunct clinical professor at State University of New York College of Optometry, Illinois College of Optometry and New England College of Optometry.
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