(Translation from Russian, courtesy of Dr. Jaime Etxebarría Ecenarro)

Vladimir Petrovich Filatov did the first attempt to implant keratoprostheses in our country in 1935, but a few months later said keratoprosthesis was extruded¹. In 1966, the academic Nadezhda A. Puchkovskaya, from the Filatov Institute, started again the use of keratoprosthesis. Subsequently, from 1968 to the present, this work has been carried out by us^2,3. We will present a retrospective analysis of 5 decades of keratoprostheses at the Filatov Institute in Odessa, Ukraine.

DEVELOPMENT OF THE KERATOPROSTHESIS

In the 1960s, experimental studies were initially carried out for the selection of materials for the manufacture of keratoprostheses, their design and the surgical implantation technique⁴. Subsequently, this knowledge was implemented in the clinic. In both situations, keratoprostheses with an optical cylinder of methyl methacrylate (PMMA) with diameters anterior of 3.3 mm and posterior of 2.6 mm were used. The height of the anterior part was wider between 0.6 and 2.4 mm depending on the thickness of the patient's cornea. For support and fixation to the cornea (interlaminar) tantalum is used, which is an inert material and very resistant to corrosion.

The first results showed that keratoprostheses were useful to restore vision in patients with corneal opacities that were previously considered hopeless⁵. The percentage of extrusion of these was, however, quite high (30%), although comparable to other studies of the time^6-10. From 1972 onwards, we began to use the so-called "open-work" keratoprosthesis in the clinic, which significantly reduced the extrusion rates¹¹. However, we made several design modifications¹²: between the years 1972-1974, the Puchkovskaya-Iakimenko-Golubenko model (N=70); between 1975-1977, the non-demountable Iakimenko-Golubenko model (N=157); from 1978 to the present, we have used our "universal removable" design (Figure 1) which, due to its characteristics, allows us to avoid the most serious complications or to fight them successfully (N=793).

SURGICAL TECHNIQUES

An important factor in the increase in the efficacy of keratoprosthesis was the application, since 1974, of a surgical method in two stages¹³. In a first phase, a lamellar dissection is performed from the limbus at a maximum depth, the external corneal layer is lifted, and a 2.5 mm diameter trepanation of the posterior layer is performed. If necessary, through this hole, the lens is removed, and an anterior vitrectomy is performed, which can also be done through a limbal incision. Through this trepanation, the rear part of the optical cylinder is inserted, already fully assembled in the keratoprosthesis, which is then covered with the front (non-trepanned) layers of the cornea. The limbal incision is closed with sutures.

The second phase is carried out 3 to 5 months later. Only the superficial corneal layers on the optical cylinder are trepanned to a diameter of 3.5 mm. This method creates the optimal conditions for the adaptation and encapsulation of the keratoprosthesis within the corneal opacity, and thus prevent complications such as external filtration of the intraocular fluid and extrusion (Figure 2).

Another important factor to achieve sustainable results was to reinforce the cornea in which the keratoprosthesis is attached. This reinforcement can be superficial (epicorneal) or intracorneal. The first is performed 5-6 months before implanting the keratoprosthesis, using a donor cornea or oral mucosa of the patient. The second is done during the first phase of keratoprosthesis surgery, either with a donor lamellar corneal graft (posterior stroma with Descemet's membrane), with dura mater or with patient's auricular cartilage. All of them are carved with trephines of 9-10 mm and a central trepanation of the size of the optical cylinder (3.3 mm). This reinforcing sheet is placed on the posterior layers of the cornea before implanting the keratoprosthesis or just after. One or the other will be used depending on the nature of the corneal opacity.

We have found that the most reliable corneal reinforcement to give stability to keratoprostheses is achieved by the combination of oral epicorneal autologous mucosa plus an intracorneal auricular cartilage autograft. Most of these reinforcements are made in vascularized corneal opacities, especially after burns. When the opacities are avascular or in corneal dystrophies, epicorneal reinforcement with oral mucosa usually fails and better results are obtained by intracorneal reinforcement with posterior layer grafts of donor cornea¹⁴.

RESULTS

In the period between 1972 and 2010 we implanted our keratoprostheses in 1060 eyes of 1040 patients, that is, in 20 of them the surgery was carried out bilaterally. 987 prostheses were placed penetratingly, 23 of anterior lamellar type – the prosthesis reaches the anterior surface but does not penetrate the anterior chamber –, 30 lamellar posterior type – penetrate the anterior chamber but does not reach the external surface –, and 20 were "optical-cosmetic" – penetrating but with a built-in cosmetic contact lens. In all patients, keratoprosthesis was the only method capable of offering visual recovery. In many of them, several types of keratoplasty had previously been performed unsuccessfully.

The etiologies of the corneal opacities included: eye burns in 725 eyes (68.4%), penetrating corneal trauma in 120 (11.3%), keratitis, keratouveitis, corneal or pemphigoid ulcers in 108 (10.2%), and severe edematous (bullous) keratopathy in 107 (10.0%). The preoperative visual acuity (VA) was of light perception in 962 eyes (91%) and between 0.005 and 0.2 in the remaining 98 (9%). 932 patients (90%) were almost blind, with VA <0.005 in both eyes. The age of the patients was between 11 and 82 years, with blindness time before keratoprosthesis from 1 to 52 years. There was a marked predominance of men (N=793) over women (N=247). In 1023 eyes (96.5%) the keratoprosthesis achieved some degree of VA improvement (when using VA limit ≥ 0.005) and 721 eyes (68.0%) reached VA between 0.1 and 1.0.

COMPLICATIONS

In a part of the patients, however, there were different complications in the postoperative period, which led to a reduction or even loss of the VA initially recovered. Aseptic late necrosis occurred in the fixation area of ​​the prosthesis or around the optic cylinder in 24.5% of the 227 patients operated between 1972 and 1978, but only in 5.6% of the 793 operated between 1978 and 2010. This led, in the first group, to 13.3% of extrusion, 6.4% of severe uveitis with phthisis bulbi and 3.5% of endophthalmitis. However, in the most recent group, these complications were reduced to 2.0%, 2.4% and 1.0% respectively. The figures are even better if we only take patients since 1995, when we started using a combination of epicorneal and intrastromal reinforcement. In the rest of the cases with aseptic keratolysis, keratoprosthesis was saved thanks to different strengthening methods.

Keratoprosthesis extrusions occurred mainly in the first stages after surgery: 53.4% ​​in the first 2 years; 36.2% between the 3^rd and 5^th year, and 10.3% beyond 5 years. Retinal detachment occurred in 12 patients (1.1%) and terminal glaucoma in 19 eyes (2.4%). This type of more serious complications resulted in the loss of vision in 107 eyes (10.1%), all with long-term follow-ups between 5 and 43 years.

The most frequent complications were the formation of retroprosthetic membranes of different density in 16.7% of the patients, and the growth of tissue on the optic cylinder – corneal epithelium, fibrous tissue or the same used as a coating to reinforce the cornea – in 22.3%. However, in most cases, these complications did not significantly affect VA or, if they did, they were surgically removed. VA remained the same until the end of the follow-up period in 953 eyes (89.9%), with VA between 0.1 and 1.0 in 583 (55%). The maintenance of VA in these patients is achieved thanks to the good fixation of keratoprosthesis in the cornea, in 93% of patients.

In conclusion, our best results were obtained with the use of "universally removable" keratoprosthesis, with a two-stage surgery, and the widespread use of different forms of corneal reinforcement. The development and learning with our keratoprosthesis has proven to be an effective long-term method to restore vision in patients with severe corneal opacities in which keratoplasty is not indicated.