Anterior-segment OCT (AS-OCT) and Intraoperative OCT (iOCT) for Trans- Conjunctival Needle Revision (TCNR)

Trabeculectomy is one of the most commonly performed glaucoma procedures performed to control IOP with approximately 18,000 operations performed in US Medicare beneficiaries alone in 2012. One complication of trabeculectomy surgery is the formation of subconjunctival and episcleral fibrosis, which occurs as part of the wound healing process and can result in fibrosis of the filtering bleb and failure. Transconjunctival needle revision (TCNR) aims to lyse subconjunctival adhesions and reestablish adequate aqueous humor flow from the anterior chamber to the subconjunctival space. One study reported 17% of trabeculectomies require bleb-needling revision. During TCNR the surgeon is able to visualize the trajectory of the needle or blade under the conjunctiva; however, detection of the fibrotic tissue and determination as to whether that tissue has been adequately lysed is difficult, limiting the success rate of the procedure. Anterior segment optical coherence tomography (AS-OCT) allows for detailed assessment of the internal morphology of the bleb. Studies have utilized AS-OCT to assess morphological features of the bleb and correlate it with surgical success. A small case series reported the utility of AS-OCT for pre-operative planning for bleb revision, in particular, identifying safe access sites and minimizing conjunctival dissection. More recently, real time OCT integrated with operative microscope has become available. Intraoperative OCT (iOCT) has been utilized extensively in retinal surgery and corneal surgery. Dada et al., described performing iOCT-guided TCNR in 2 patients with failed trabeculectomy blebs without intraoperative or postoperative complications. Investigators reported they were able to obtain a detailed view of the bleb wall and assess the depth and location of the needle, which permitted better lysis of adhesions. A pilot study by Kumar et al., reported one case of TCNR in which iOCT was used to demonstrate the extent of adhesions and loculations inside the bleb at the beginning of the procedure, and the lysis of these adhesions and formation of large single hyporeflective cavity inside the bleb at the end of the procedure. These small case studies suggest a role of iOCT imaging for TCNR, however, further research is needed to assess its feasibility and utility for routine use. The aim of the research is to assess the surgical success, feasibility and utility of pre-operative Anterior Segment Optical Coherence Tomography (AS-OCT) and intraoperative Optical Coherence Tomography (iOCT) in trans-conjunctival needle revision (TCNR) of trabeculectomy bleb. Furthermore, investigators want to assess whether AS-OCT can be used to identify characteristics of trabeculectomy blebs that are associated with successful surgical outcomes. To undergo this study, investigators will conduct a prospective study of patients who consent to AS-OCT and iOCT revision of TCNR. Investigators will compare the outcomes of these patients with retrospectively identified, historical controls (i.e. patients who underwent TCNR by the same surgeon without AS-OCT or iOCT assistance). investigators hypothesize that information gained from pre-operative AS-OCT and intraoperative OCT will aid with intraoperative decision-making for TCNR of trabeculectomy bleb and will thereby improve surgical outcomes. Investigators also hypothesize that preoperative AS-OCT can be used to identify features of trabeculectomy bleb that can predict success with iOCT-assisted TCNR. More specifically, investigators hypothesize that filtering blebs with more extensive scarring as seen on pre-operative AS-OCT will benefit from iOCT.