This retrospective study examined the incidence of glaucoma after implantation of the Boston type 1 keratoprosthesis (KPro) at one institution. The authors found that glaucoma development or progression of pre-existing glaucoma was a significant cause of postoperative visual loss. They conclude that while the Boston type I KPro is an effective option for managing eyes with poor prognosis for primary or repeat penetrating keratoplasty, visual potential is limited by preoperative comorbidities. They recommend aggressive perioperative management of glaucoma and elevated IOP, including preoperative and concomitant glaucoma surgery, since determining which eyes are at risk for acute IOP elevation or late glaucoma development is challenging.
The study included 29 patients (30 eyes) who underwent 36 KPro procedures. Follow-up was at least three months, with mean follow-up of 17 months (range, 3 to 67 months). Corneal graft failure was the indication for KPro in 77 percent of cases.
Median preoperative BCVA was hand motions, which improved to 20/330 (range, 20/20 to hand motions) at nine months postoperatively and 20/600 (range, 20/40 to no light perception) at last follow-up.
Twenty eyes (67 percent) had a preoperative history of glaucoma, with eight eyes (40 percent) having undergone previous glaucoma surgery. Twenty-one eyes (70 percent) underwent concomitant glaucoma surgery.
Increased postoperative IOP (22 mm Hg or higher) was noted in 15 eyes (50 percent), with definite glaucoma development or progression found in 7 of those 15 eyes (23 percent of total eyes). Mean BCVA at last follow-up in eyes with glaucoma development or progression was 3/200 compared with 20/563 in the remaining eyes.
Six patients (20 percent) required repeat KPro implantation, and retroprosthetic membranes developed in 23 eyes (77 percent), which is higher than previously reported rates.
Patients with adequate control of IOP through either medical or surgical intervention during the perioperative period fared better than those without. In patients with a preoperative diagnosis of glaucoma and aggressive preoperative IOP control, mean postoperative IOP was lower and fewer glaucoma medications were added postoperatively. Eyes with previous glaucoma surgery were less likely to experience glaucoma progression or elevated IOP after KPro implantation.
KPro implantation appeared to increase the risk for glaucoma development or progression. The authors postulate that the mechanism of increased IOP in eyes implanted with KPro is multifactorial, including gradual closure of the angle from peripheral anterior synechiae, abrupt blockage of the angle from the KPro device itself, inflammation, bleeding and vitreous debris. Unintentional occlusion of the tube occurred in some patients who underwent combined surgery with a glaucoma drainage device implanted into the anterior chamber. Five such eyes required tube revision surgery.