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

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

Trabeculectomy is a very important and commonly performed glaucoma operation. It allows fluid from inside the eye to exit into a space called a bleb located on the surface of the eye under the upper eyelid. The formation of excessive scar tissue after surgery may cause the operation to work less well or stop working. This results in an increase in eye pressure. The use of a needle to cut the scar tissue is a commonly used procedure. This surgery is called trans-conjunctival needle revision (TCNR) of trabeculectomy bleb.

The study aims to determine if advanced optical imaging called Optical Coherence Tomography (OCT) of the scar tissue both in the office prior to surgery and during surgery in the operating room improves the success rate of the revision surgery. These devices are FDA approved and have been used extensively in ophthalmology and ocular surgery.

Ophthalmologists already used these imaging devices for this purpose as part of the standard medical care of some patients. The purpose of this study is to prospectively gather information about its use in a systematic way. Furthermore, investigators want to determine if imaging improves outcomes compared to historical controls (patients who underwent the same surgery in the past without imaging). The potential benefit of this research is that it may provide knowledge that will be of benefit to future patients with glaucoma who are undergoing this procedure.

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.

Inclusion criteria

• Briefly, the diagnosis of glaucoma is based on the presence of 2 or more of the following findings: 1) glaucomatous optic disc damage, defined as the presence of optic disc excavation, diffuse or focal neuroretinal rim thinning or notching, localized or generalized retinal nerve fiber layer (RNFL) thinning; 2) visual field defects consistent with glaucoma; and 3) IOP ≥ 22 mmHg.
• Patients with glaucoma who have been advised to undergo TCNR of a failed trabeculectomy bleb by a glaucoma specialist at Northwestern Medicine
• History of failed trabeculectomy (based on clinical features of the trabeculectomy bleb and elevated intraocular pressure)
• Patients can have history of other glaucoma surgery or cataract surgery
• The diagnosis of glaucoma is based on the presence of 2 or more of the following findings: 1) glaucomatous optic disc damage, defined as the presence of optic disc excavation, diffuse or focal neuroretinal rim thinning or notching, localized or generalized RNFL thinning; 2) visual field defects consistent with glaucoma; and 3) IOP ≥ 22 mmHg.

Exclusion criteria

• Age younger than 18 years;
• Secondary causes of glaucoma (e.g., iridocyclitis, trauma);
• Any evidence of corneal or conjunctival pathology adjacent to filtration bleb that could influence AS-OCT image
• Patients who did not undergo surgery or have adequate follow up
• Adults unable to consent, individuals who are not yet adults (infants, children, teenagers), pregnant women, prisoners and vulnerable populations