Inclusion Criteria:  Consecutive patients who had undergone glaucoma drainage device implantations between January 2006 and December 2016 at Siriraj hospital by or under supervision of one surgeon (NK). The GDD implantation using glycerin-preserved, human-donor, corneoscleral tissue as a patch graft  Exclusion Criteria:  1.Patients who had follow-up period less than 12 months after operation.