Keratoprosthesis: procedure of choice for paediatric corneal opacities
Aiming for amblyopia prevention & therapy
Attitudes need to change
Other paediatric ophthalmologists, particularly in North America and Asia, have been impressed with recent efforts to treat unilateral amblyopia and establish improvement in visual potential even when these efforts are initiated after the first several months of life. Dr Krystel Huxlin working in her laboratory at our University of Rochester Eye Institute, New York, USA, has demonstrated success in having stroke victims utilize unaffected areas of the brain to perceive visual images. With this evidence of brain plasticity in adults, presumably there exists significant potential for amblyopia therapy in infants.
While bilateral congenital blindness as evidenced in Peters Anomaly, congenital glaucoma, congenital hereditary endothelial dystrophy, and a variety of still less frequent developmental defects, present a significant problem, the standard therapeutic modality of corneal transplantation is now recognized as being associated with a very poor prognosis. This is primarily as a result of repeated graft failure in the face of an active immune system. Even in the instance of a clear graft, the attendant inflammation, irregularity, and astigmatism continue to constitute major obstacles to amblyopia prevention and therapy.
Replacing corneal transplantation and dispelling the myths
Keratoprosthesis has been perceived as an infrequently performed procedure indicated only in extraordinary cases of bilateral blindness and associated with poor prognosis as a result of infection, reoperation, and extrusion.2 Only a few centres have demonstrated interest in the procedure over the past several decades and, as recently as the 1990's, only a handful of procedures were performed worldwide. The results continued to be poor.
Under the direction of Professor Claes H. Dohlman, a variety of modifications were introduced in the design and manufacture of the Boston Keratoprosthesis. Concurrent changes in surgical procedure and postoperative management continued to be evaluated at the University of Rochester Eye Institute.
These design changes constituted a reduction in the diameter of the methylmethacrylate surface flange, the fenestration of the back plate, and the addition of a titanium-locking ring. Mounting of the device on a ring of donor cornea enabled a simplified surgical approach. Covering the implanted device with a large bandage contact lens and the use of a prophylactic antibiotic regimen were effective in preventing surface ulceration and infection. Close attention to inflammation and elevated intraocular pressure (IOP) were ongoing. As a result, these devices began to be utilized in Rochester and Boston with a high degree of success. In the adult population free of autoimmune disease, hundreds of cases were performed with no infections, no re-operations, and no extrusions of the prosthesis.
Evaluation of the optics of the device revealed no astigmatism, a wide visual field, and no alterations in colour vision. In addition, the eyes were generally not inflamed and achieved their maximum visual potential in a matter of weeks as opposed to the many months required for rehabilitation following a corneal transplant.
Translating success to the paediatric population
I postulated that the success with the adult population warranted the use of keratoprosthesis in infants as an alternative to the largely discredited traditional corneal transplantation in this population. Our work at the University of Rochester Eye Institute continues to support this hypothesis.
Over the past 36 months 45 paediatric eyes, the majority of young infants, have been implanted with the Boston Keratoprosthesis. Initial results were reported at the 2006 Annual Meeting of the American Academy of Ophthalmology and more recently in a publication in the journal Ophthalmology.1
The original study included 17 infants who had been previously subjected to over 100 surgical procedures including 39 failed traditional transplants. A similar number of infants' eyes received a prosthesis as the initial procedure, with bilateral procedures being performed a week apart. These congenital defects are not infrequently associated with other significant vitreoretinal disease, dysgenesis, glaucoma and inflammation.