What are they?
Keratoprostheses are "artificial corneas" that help restore vision in situations where the cornea and the eye surface are so affected that a cornea transplant would not be viable. The idea is as simple as making a window in the wall of a house in order to see through it.
One of the most commonly used keratoprostheses is the Boston keratoprosthesis (B-Kpro). More than 15,000 units have been implanted throughout the world. Our Centre has more than 40 years' experience in different keratoprostheses; in the case of B-Kpro we have been successfully performing these procedures more than 10 years.
What does the treatment involve?
B-Kpro basically involves a "mushroom-shaped" plastic optical stem (PMMA) that acts as a lens around which a donor cornea is positioned, a back titanium plate is then added to prevent the cornea from detaching from the optical stem.
The back titanium plate gives the eye a blue-ish colour once the prosthesis is implanted. B-Kpro surgery differs very slightly from standard cornea transplant surgery. Once the prosthesis is assembled with the donor cornea, the complex is implanted in the patient's eye in an identical way to a cornea transplant, with sutures.
When is this treatment indicated?
B-Kpro indications include corneal pathologies with dense opacities in which a cornea transplant would not work or would fail early.
For this implant to be a success, it is essential that the eyelids are healthy, can close properly, and that there is enough tear production.
It is also important to determine the condition of the optical nerve and the retina, to the extent the cornea permits.
The pathologies that could benefit from a B-Kpro are: multiple failed cornea grafts, non-inflammatory corneal oedema, some dystrophies and cornea degenerations, lumbar deficit, aniridia, cicatricial leukoma after inactive infectious keratitis (herpes simplex or zoster, bacteria or fungus), corneal neovascularisation, burns (chemical and thermal), Stevens-Johnson syndrome, ocular pemphigoid, serious atopy, graft-versus-host disease and some cases of uveitis.
Results
The visual results are excellent in some cases where the risk of complications is low (for example, multiple failure, non-inflammatory corneal oedema, cicatrical leukoma, corneal neovascularisation); these patients can end up having vision close to one.
In the most complicated cases–burns and autoimmune diseases–in which the risk of complications is high, success will depend on their control. Still, in these cases visual recovery, although not permanent, can very often mean leading a productive and relatively normal life, with good eyesight.
It is very important to explain the limitations of the technique to the patient, without giving them unrealistic expectations that may affect them emotionally if they are not met.
Possible risks
It is essential to bear in mind that patients who need a B-Kpro are complicated cases with associated pathologies, mainly glaucoma, which may affect the long-term success of the prosthesis.
It is important to remember that these patients will need to use a therapeutic contact lens and use topical antibiotic drops on a daily basis for the rest of their lives. Furthermore, they must undergo regular postoperative check-ups (6 months after surgery, every 3 months maxium) to control the possible complications that may arise.
The main risks include cornea infection, endophthalmitis (inflammation of the whole inside of the eye), glaucoma (a new case or worsening of the same case), retinal detachment and cornea necrosis (the donor cornea "comes away" and gets thinner until it becomes perforated; in these cases, the cornea would have to be replaced with another or surgery would have to be perormed to cover the hole with a cornea patch).