Fig. 25.1
(a) Fyodorov–Zuev keratoprosthesis from anterior view, (b) in an artificial anterior chamber, (c) from anterior view before with prosthesis embedded into the cornea just before the transplant, and (d) during the transplant
The temporary insert and the optical cylinder are both made of polymethyl methacrylate. Both the temporary insert and the optical cylinder are 2.6 mm in diameter and possess external threading that correspond to the internal threading of the central opening of the supporting titanium plate. The total length of the temporary insert and the optical cylinder is 2.8 mm. The power of the optical cylinder ranges from +48.00 to +77.00 diopters. The power of the optical cylinder is chosen according to axial length of the eye as measured by A-scan ultrasonography [2].
25.2.1 Patient Selection
Patients selected for Fyodorov–Zuev keratoprosthesis must be at least 18 years of age, their visual acuity should be between 20/400 and LP in the better eye, and they must have a history of at least two previous failed corneal grafts.
Fyodorov–Zuev keratoprosthesis is not offered to the patients with the following conditions: glaucoma, retinal disease, amblyopia, phthisis bulbi, and recalcitrant intraocular inflammation. Furthermore keratoprosthesis is not offered to patients with potential for successful surgical outcome after penetrating keratoplasty, patients with history of ocular surgery in the past 6 months, and those who cannot administer topical eye drops or unable to follow up with an ophthalmologist.
The preoperative evaluation includes detailed medical and ocular history, assessment of the visual acuity, slit-lamp examination, and intraocular pressure measurements. Light projection and color discrimination should be used in selected individuals to evaluate the visual potential of the eyes. When the posterior pole cannot be visualized, B-scan ultrasonography must be performed to exclude any preexisting retinal or optic nerve abnormalities [2].
25.3 Surgical Procedure
The surgery can be performed in either two separate stages 3 months apart or in a single stage. Both techniques have similar clinical outcome and comparable rate of complications.
25.3.1 Two-Stage Surgery
25.3.1.1 Stage 1
The first stage consists of creating a lamellar corneal flap and insertion of the implant into the pocket created. In this technique the superior bulbar conjunctiva is first removed. Using a crescent blade, a 5 mm corneal incision at approximately half depth is performed 2 mm anterior to the limbus. Using the crescent blade, a corneal flap measuring approximately 6 × 8 mm is then created. The temporary optic is screwed into the central opening of the supporting titanium plate. The supporting titanium plate is then inserted into the lamellar pocket. The corneal flap is then repositioned, and it is secured in place with interrupted 10.0 nylon sutures, sandwiching the Fyodorov–Zuev keratoprosthesis within the corneal stroma. Conjunctival incisions are closed with 6-0 absorbable sutures. In patients with a peripheral corneal thickness of less than1.0 mm, the cornea is usually reinforced by placing an autologous auricular cartilage or tibial periosteum between the supporting plate and the anterior corneal lamellae.
25.3.1.2 Stage 2
Stage 2 of the surgery is performed 3 months after completion of stage 1. Stage 2 is marked by the removal of the temporary insert and insertion of the optical cylinder. A 2.5 mm hole is trephined in the center of the cornea, exposing the temporary insert underneath. The temporary insert is then unscrewed from the supporting plate. Next, using a surgical blade, a circular hole with a diameter of 2.2 mm is created in the posterior cornea lamellae. The optical cylinder is then screwed to the supporting plate [3, 4].
25.3.2 One-Stage Surgery
Prior to starting the surgery, the donor cornea with its scleral rim is mounted on an artificial anterior chamber. The center of the cornea and the peripheral 9.0 mm trephination site is marked with a sterile skin marker. A 5 mm corneal incision is made, 2 mm anterior to the limbus. Lamellar dissection is then carried out at approximately half depth with a crescent blade. After completing the lamellar dissection, the supporting titanium plate with the attached temporary insert is inserted and sandwiched between the anterior and posterior corneal lamellae; the corneal incisions are then sutured with 10.0 nylon.
In the next step, a 2.5 mm hole is created in the center of the cornea using a 2.5 mm trephine exposing the temporary insert. The temporary insert is then unscrewed and removed. A 2.5 mm hole is then created in the posterior corneal lamella using a surgical blade, entering the anterior chamber. Optical cylinder is then screwed into the central opening of the supporting plate. The donor corneal tissue with the implanted Fyodorov–Zuev keratoprosthesis is punched using a 9 mm trephine. The cornea–keratoprosthesis complex (Fig. 25.1b) is then removed from the artificial anterior chamber and transferred onto the recipient cornea. An 8.5 mm trephine is used to excise the recipient cornea; the cornea–keratoprosthesis complex is then sutured to the recipient cornea using 10.0 nylon (Fig. 25.1b–d).
In phakic eyes, extracapsular cataract extraction, posterior capsulotomy, and anterior vitrectomy are routinely performed. In pseudophakic eyes, the intraocular lens is removed before posterior capsulotomy and vitrectomy. In patients who are at high risk for a corneal melt (i.e., dry eyes, ocular cicatricial pemphigoid, Sjögren’s syndrome, Stevens–Johnson syndrome, graft-versus-host disease), the cornea is covered with a conjunctival flap or labial mucosal membrane graft. Patients are advised to wear eye shield at bedtime.
Postoperatively systemic ciprofloxacin 750 mg daily for 1 week or systemic doxycycline 100 mg daily for 1 month is used. Topical medications include topical prednisolone acetate (1 %) four times a day and a topical fluoroquinolone four times a day, for a total of 4–6 months. The topical prednisolone acetate and fluoroquinolone are tapered in most cases to twice daily over a 4–6 month period. Patients are instructed to use preservative free artificial tears several times a day.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
