We read with interest the article “Long-term Complications Associated with Glaucoma Drainage Devices and Boston Keratoprosthesis.” This study is a retrospective cases series that suggests that complications associated with glaucoma drainage devices can cause significant vision loss in keratoprosthesis patients. We agree with the authors in that postoperative glaucoma management is one of the significant challenges that we face in keratoprosthesis surgery and that many patients continue to loose vision despite close monitoring by glaucoma specialists.
We find this to be a valuable article that alerts corneal and glaucoma surgeons involved in the care of these patients to the fact that traditional techniques for valve placement may be inadequate given the high rate of complications, which include erosion of the conjunctiva, tube exposure, and extrusion. The use of a contact lens over the keratoprosthesis, although necessary to protect the ocular surface, can contribute to erosion of the tissue covering these devices.
We would like to share with the authors our technique for valve placement in keratoprosthesis patients that has decreased significantly, if not eliminated, these complications at our institution. We place an Ahmed valve (FP7; New World Medical, Inc, Rancho Cucamonga, California, USA) preferably in the supertemporal quadrant. After conjunctival dissection, the plate is fixed 8 mm from the limbus. We proceed with keratoprosthesis implantation and pars plana vitrectomy. Direct visualization through the keratoprosthesis and a transillumination technique aids in identifying the limbus and in safe introduction of a 23-gauge needle approximately 5 mm from the limbus. We do not use the pars plana clip in these eyes because of the risk of exposure based on previous experience. After securing the tube, a partial thickness corneoscleral graft from the corneal rim is cut (approximately 3 × 4 mm) and is used to cover the tube. The conjunctiva then is closed using a standard technique.
Together, the more posterior pars plana tube placement and the use of a lamellar corneal patch graft have the following advantages: (1) permitting direct visualization for examination of the tube entry after surgery; (2) improving contact lens fitting by creating a thinner and much smoother surface compared with the Tutoplast (IOP Ophthalmics, Costa Mesa, California), allowing adequate fit of various-sized contact lenses and eliminating friction between the contact lens edge and the tube or plate; (3) decreasing the risk of conjunctival erosion or tube exposure and extrusion. We have observed cases of extrusion in pre-existing shunts placed with the conventional technique, but with the above technique, we have not observed any extrusion in 4 years of follow-up. However, longer follow-up is required, and we recommend close monitoring and early repair of any shunt exposure to avoid sight-threatening complications.
In summary, we believe that an interdisciplinary approach optimizing surgical techniques for glaucoma drainage devices and for the Boston type I keratoprosthesis can avoid shunt-related complications, and therefore can achieve the best visual rehabilitation in these patients.