To our knowledge investigating the site of trabeculectomy failure with surgical revision have not been reported before,so this is the first study that report the site of trabeculectomy failure with opening the conjunctiva and determine the site of aqueous flow obstruction.

The patients who underwent surgical revision for failed trabeculectomy between February 2011 to december 2015 at farabi eye hospital were reviewed.exclusion criteria include previous needling or other procedure befor revision. Surgical technique: One surgeon (Y.E.) performed all surgeries. After administering a subconjunctival injection of lidocaine 2 % and placing a superior rectus bridle suture, a fornix-based peritomy was created.the tenon and scar were excised just enough to establish adequate aqueous flow.if aqueous flow did not exist then dissection continue to episclera and then scleral flap was lifted.the site of failure detected by surgeon when the aqueous outflow restored. The anterior chamber was formed with balanced salt solution (BSS) and the scleral flap was left without any suturing. Finally, the conjunctival incision was sutured using a 10-0 nylon suture.

We reviewed the charts of 46 eyes of 46 patients who underwent surgical revision for failed trabeculectomy.The mean age of the patients was 52.8 years(range 6-79 years).Twenty eight(60%) patients were male.Sclera was the site of failure in 28 (60.8%) patients.episclera in 16(34.7%) and subconjuctive and tenon in 2(4.5%) patients.

The main finding of this study is that the most common site of outflow obstruction in failed trabeculectomy procedure is the sclera(60.8%).we must consider that although needle revision has been described with raising the scleral flap and entering the anterior chamber, being a blind procedure, it may be associated with other potential complications, and according to this study episclera and sub-tenon responsible for 39.2% of outflow obstruction and sub-Tenon needling alone may be a better alternative if subscleral flap entry can be avoided.