The latest devices

Advances in biomaterials and design allied to enhanced surgical techniques are helping to deliver improved results with the latest generation of keratoprosthetic devices, according to Günther Grabner MD.
“We still have a lot of work to do, but we are definitely making steady progress in achieving better outcomes for patients with severe ocular disease who are at high risk for donor graft failure,” Dr Grabner, Paracelsus Private Medical University, Salzburg, Austria, told EuroTimes.
Implantation of a keratoprosthetic device is generally undertaken when other surface reconstruction methods for visual rehabilitation have failed, or are deemed unfeasible, said Dr Grabner. Candidates would include those with severe bilateral chemical or thermal injury, and patients with ocular cicatricial pemphigoid or Stevens-Johnson syndrome.
While there are several designs of keratoprosthesis available, only two are widely used today: the Boston KPro type 1, developed at the Massachusetts Eye and Ear Hospital by Dr Claes Dohlman; and osteo-odonto-keratoprosthesis (OOKP), first developed by Strampelli in the 1960s and later improved upon by Falcinelli.
“They are generally used as a last resort to avert corneal blindness and are indicated for a variety of diseases that have not responded to treatments such as stem cell or amniotic membrane transplantation and penetrating keratoplasty,” Dr Grabner said. 
As surgeons have become more familiar with the various devices, so treatment protocols have evolved to help ensure the best chance of a favourable outcome for the patient.

TREATMENT OF CHOICE
“The choice of KPro device to use will depend on a number of factors, such as whether the disease is unilateral or bilateral, if there is a complete loss of stem cells and whether the ocular surface is wet or dry,” added Dr Grabner.
When there is a bilateral loss of stem cells but a wet surface, a Boston KPro is the treatment of choice, but if the eye is dry and the patient has usable, healthy teeth, then the modified OOKP is usually the best option, said Dr Grabner.
“The new types of Boston KPro are very acceptable for cases with a wet ocular surface, but very difficult to handle in the long-term in cases with insufficient wetting such as Stevens-Johnson syndrome and graft-versus- host disease,” Dr Grabner added.
Furthermore, the progressive nature of the disease means that constant vigilance is necessary even after successful implantation of a KPro device, he warned.
“These are cases that have an innate progression in the disease course which also involves the surface of the eye. So while you might be doing quite well in the beginning with the Boston KPro and the eye looks quite nice with a wet surface, as time goes on the disease progress also catches up on the eye. We then find ourselves with a patient who has been doing well for six months and comes back after a year or two with a disastrous outcome,” he said.

BETTER SOLUTIONS
There is, however, still some hope for such patients in the form of the Boston type II device designed specifically for severe end-stage ocular disease, said Dr Grabner. 
“The type II device is much more difficult to implant surgically, but we will know more about the outcomes when the Boston group publishes its results in the near future,” he said.
While OOKP has successfully saved sight in patients with severe bilateral end-stage disease, the procedure is still only performed by a handful of surgeons worldwide, said Dr Grabner.
“The field of ocular surface reconstruction urgently requires better solutions to deal with surface and secondary issues such as dry ocular glaucoma. New innovations, such as the bioengineered cornea from LinCor Biosciences or the bio-coated MIRO CORNEA (Miro GmbH), could give even better results combined with corneal crosslinking and newer topical drugs such as the Cacicol eye drops (Laboratoires Théa),” he concluded.

Günther Grabner: g.grabner@ophtha-consult.at