• PURPOSE: To report the occurrence of chronic hypotony as a complication following Boston type 1 keratoprosthesis (KPro) implantation and to determine associated risk factors. • DESIGN: Retrospective case series. • METHODS: The medical records of all patients undergoing KPro implantation between January 2004 and November 2010 at the Wilmer Eye Institute were reviewed. Patients who developed chronic hypotony following Boston type 1 KPro implantation not attributable to anatomic problems (eg, retinal detachment, overfiltering glaucoma tube shunts, tissue necrosis with aqueous leak) or other causes were identified. Demographics and preoperative, intraoperative, and postoperative clinical findings were analyzed. Light microscopic examination of an enucleated globe as well as fibrous retroprosthetic membranes excised at the time of vitrectomy from another patient was performed. • RESULTS: Sixty-eight eyes received KPro implantation over the study period. Six eyes experienced chronic hypotony, with a median time of 18.5 months between KPro implantation and the onset of hypotony. The incidence of chronic hypotony in this series was calculated to be 3.7% at 1 year (95% CI = 0.9%-14.0%) and 13.3% at 2 years (95% CI = 5.5%-30.0%). Of the 6 eyes that developed chronic hypotony, 5 had a previous history of glaucoma or ocular hypertension, but only 3 had a glaucoma drainage implant. All eyes progressing to chronic hypotony were noted to have a retroprosthetic membrane prior to the onset of hypotony. Cox regression modeling demonstrated an increased risk of chronic hypotony in eyes with retroprosthetic membranes (P < .01) but no increase in risk for older patients (P > .1), eyes with glaucoma drainage implants (P > .5), or a previous history of multiple donor corneal transplants (P > .5). • CONCLUSION: Chronic hypotony can be a significant complication of KPro implantation and should be assessed carefully in eyes with retroprosthetic membranes. Further study of an association between hypotony and retroprosthetic membrane formation may be useful to gain insight into the mechanism of this complication and potential prevention or treatment options.
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