KeraKlear keratoprosthesis an option for treating corneal blindness
A second generation of the artificial cornea addresses more corneal issues and indications.
Corneal opacity and scarring secondary to a wide spectrum of infectious and inflammatory corneal diseases are a major cause of global blindness. Worldwide, about 45 million people are blind, and corneal blindness is the second leading cause, with about 4.9 million people having bilateral corneal blindness.
Corneal blindness with a healthy posterior segment is often surgically reversible, and keratoprosthesis may be one of the avenues to achieve this goal, especially in cases of high-risk graft failure. With advances in keratoprosthetic devices, there is a move toward using these devices as a primary transplantation procedure in select patients. However, currently popular commercially available keratoprosthetic devices require a donor cornea, and demand exceeds supply, thus limiting the outreach of corneal transplantation to those who need the procedure.
Some of the favorable uses of the foldable keratoprosthesis described in this article include the elimination of the need for a donor cornea because the device is housed within the recipient cornea and does not violate the interior of the globe. Further, it does not enter into or alter the anterior chamber anatomy, and hence, there is usually no secondary glaucoma associated with this keratoprosthesis. Continued research is required to further improve the interactions between human corneal tissue and the prosthetic materials for longer lasting residence within the recipient cornea, without tissue melt or extrusion of the device over time.
In this column, Drs. Shiuey and Vargas describe the KeraKlear foldable keratoprosthesis (KeraMed), the surgical implantation technique and early results. This device is not FDA approved in the U.S.
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
The KeraKlear keratoprosthesis is foldable and has a 4-mm central optic and an overall diameter of 7 mm (Figure 1). Unlike other commercially available artificial corneas, the KeraKlear is implanted using a non-penetrating technique and does not require donor tissue for implantation.
The KeraKlear artificial cornea is implanted into the cornea by using a femtosecond laser to create a uniform lamellar pocket within the cornea and to create a trephination incision. After preparation of the cornea, the KeraKlear is then inserted into the corneal pocket through the anterior opening in the cornea using non-toothed forceps. The rim of the device is then tucked into the pocket recesses. (See video for surgical technique at http://video.healio.com/video/KeraKlear- XT-implantation;Ophthalmology.) Optionally, four sutures can be placed in each quadrant. This procedure requires removal of approximately 5% of the corneal tissue volume to implant (Figure 2). Postoperatively, these patients wear a bandage contact lens and receive prophylactic antibiotic eye drops.
The 4-year results of the KeraKlear artificial cornea were presented at the 2014 EuCornea conference in London. In this study, 19 patients with corneal blindness, defined as Snellen acuity less than 20/200, received treatment with the KeraKlear. This population had a wide range of diagnoses, including failed corneal transplants, limbal stem cell deficiency, corneal scars, corneal dystrophies and keratoconus. All patients had an improvement in their visual acuity, with an average improvement of 4.2 lines of vision at the last follow-up visit. Figures 3 and 4 show before and after pictures of a patient with Reis-Bucklers corneal dystrophy who was treated with the KeraKlear. Vision improved from 20/400 preoperatively to 20/40 without correction after the KeraKlear implantation. In this series, there was one case of corneal melting in a patient with a history of chemical burn and one case of corneal ulceration in a patient who had been noncompliant with postoperative antibiotics. Importantly, this study showed that the Kera-Klear did not have some of the significant complications that have been found with penetrating keratoprostheses. There were no cases of retroprosthetic membrane, glaucoma or endophthalmitis. Over the 4-year period, 89% of the KeraKlear artificial corneas were retained.
This long-term pilot study has demonstrated the viability of using the KeraKlear as a first-line treatment of corneal blindness. This device provides rapid visual recovery with improvement in vision evident immediately when the patient leaves the surgical table and vision typically stabilizing within several weeks. The device removes approximately 5% of the corneal tissue (by volume) and is non-penetrating. Therefore, it is possible to still perform corneal transplantation, including deep anterior lamellar keratoplasty or penetrating keratoplasty, if needed.
In the past, artificial corneas were considered only for end-stage corneal blind patients who were not candidates for corneal transplantation. However, given the minimally invasive nature of KeraKlear implantation and the rapid visual recovery, it now makes sense to use the KeraKlear artificial cornea first and to reserve corneal graft tissue for those cases that truly have no other options.
In this pilot study, some of the patients with corneal edema (eg, graft failure and Fuchs’ endothelial dystrophy) did not improve as much as the patients who did not have corneal edema. This was because even after removal of the anterior corneal tissue, there was still edematous, translucent corneal tissue posterior to the implant, which limited the vision in much the same way that a partially opacified cataract will decrease vision. To address the issue of posterior corneal edema and stromal conditions that have deep opacities, as well as conditions with thinner corneas such as keratoconus, KeraMed has developed a second-generation KeraKlear artificial cornea, called the XT series.
The KeraKlear XT is available for replacement of corneal tissue from 200 µm to 700 µm in 100 µm steps. For example, if a failed graft patient has a corneal thickness of 600 µm, a KeraKlear XT500 would be selected and implanted into the corneal pocket at a depth of 500 µm after excising 500 µm of edematous tissue. This would leave only 100 µm of edematous tissue behind the implant, which is relatively transparent. In Figure 5, the central cornea is much clearer after KeraKlear XT implantation into a failed cornea transplant compared with the surrounding opaque corneal tissue. The manufacturer’s current recommendation with the KeraKlear XT model is to leave approximately 100 µm of posterior stromal tissue. However, innovations in the implantation technique of this device continue to evolve. Recently, Jorge L. Alió, MD, PhD, reported success in implanting the KeraKlear directly on top of Descemet’s membrane.
The KeraKlear is limited to investigational use only in the U.S.
References:Akpek EK, et al. Cochrane Database Syst Rev. 2014;doi:10.1002/14651858.CD009561.pub2.
Alio JL, et al. Eur J Ophthalmol. 2014;doi:10.5301/ejo.5000435.
Chang HY, et al. Cornea. 2015;doi:10.1097/ICO.0000000000000357.
Oliva MS, et al. Indian J Ophthalmol. 2012;doi:10.4103/0301-4738.100540.
Whitcher JP, et al. Bull World Health Organ. 2001;doi:10.1590/S0042-96862001000300009.
For more information:Yichieh Shiuey, MD, is a corneal specialist at the Palo Alto Medical Foundation. He can be reached at email@example.com.
Jose M. Vargas, MD, can be reached at firstname.lastname@example.org.
Thomas “TJ” John, MD, is a clinical associate professor at Loyola University at Chicago and is in private practice in Oak Brook, Tinley Park and Oak Lawn, Illinois. He can be reached at email@example.com.
Disclosures: Shiuey reports he is the inventor of the KeraKlear and has a financial interest. Vargas reports he is a consultant for KeraMed. John reports no relevant financial disclosures.