This article is more than 5 years old. Information may no longer be current.
Glaucoma a common complication of keratoprosthesis
Click Here to Manage Email Alerts
ABU DHABI — Glaucoma is a significant cause of postoperative visual loss in patients implanted with a keratoprosthesis, according to a surgeon speaking at the World Ophthalmology Congress here.
“The literature reports huge variations in the prevalence of glaucoma following Boston keratoprosthesis type 1 (KPro), ranging between 36% and 80%. Prior or concomitant glaucoma surgery was found in 47% to 84% of the cases, de novo post-KPro glaucoma in 2% to 28% of the cases, postoperative IOP elevation in 14% to 65% of the cases,” Wisam Shihadeh, MD, said.
Due to its immune privilege, the cornea tops the list of successfully transplanted solid organs. Several factors contribute to its immune privilege, including avascularity, isolation from lymphatic channels and the phenomenon known as anterior chamber-associated immune deviation. However, rejection can sometimes occur, particularly in patients with pre-existing pathologies such as Stevens-Johnson syndrome and ocular pemphigoid or with specific types of ocular trauma such as chemical burns.
“These are the cases where the Boston KPro has a role,” Shihadeh explained.
Boston KPro
The Boston KPro has been under development since the 1960s and received U.S. Food and Drug Administration clearance in 1992. Since then, over 6,000 implantations have been performed worldwide. At present, it is the most commonly used artificial cornea in the world.
The prosthesis is made of three components: a front plate with optical system, a back plate and a titanium locking ring. A button of donor corneal tissue is sandwiched between the two plates. The overall diameter is 8.5 mm in the standard model and 7 mm in the pediatric model.
The pathogenesis of glaucoma may be related to closure of the angle, either due to the formation of synechiae related to previous surgeries or to contact between the iris and the back plate after implantation of the prosthesis. In other cases, dysfunction or damage of the trabecular meshwork might occur due to inflammation or prolonged use of steroids. Intraoperative trauma might also be a cause, Shihadeh said.
Management
The management of glaucoma in such cases presents many challenges.
“Measurement of IOP might be a challenge, but expert hands can do it well by digital palpation, with accuracy within 5 mm Hg. Visual field measurement and optic nerve head evaluation, which is performed with a non-mydriatic fundus camera, are possible but not easy because of the small front optic of the prosthesis. Serial OCT imaging strictly depends on the clarity of the media,” Shihadeh said.
Treatment is also a challenge and requires team management by a glaucoma surgeon, a vitreoretinal surgeon and a corneal surgeon, he said.
If glaucoma develops following KPro implantation, topical medications are usually ineffective due to poor penetration.
“Almost three-quarters of the patients are surgically managed. Most of them have shunt surgery with sulcus, anterior chamber or pars plana implantation of a glaucoma drainage device,” he said.
Shihadeh noted that cyclodestructive procedures such as cyclodiode laser therapy, cyclocryotherapy or endoscopic cyclophotocoagulation may play a role.
Rigorous management of elevated IOP is essential for the long-term success of KPro, Shihadeh said. If glaucoma develops, the treatment should be prompt and aggressive, because glaucoma progresses quickly in these patients. – by Michela Cimberle