TRABECULAR BYPASS

Trabecular bypass procedures, including trabeculotomy and stents, are gaining ground as safer alternatives to trabeculectomy and tubes for treating glaucoma. However, they should be carefully matched to the patient, the clinical scenario and the type of glaucoma treated, Oluwatosin U Smith MD, Dallas, told a session of the 2015 ASCRS•ASOA Symposium & Congress in San Diego, USA.

Trabecular bypass procedures enhance aqueous outflow by removing or bypassing obstructions related to the trabecular meshwork (TM) and Schlemm’s canal. Therefore, a good collector system distal to the TM is required for success, Dr Smith noted. She reviewed four bypass technologies with potential as first-line glaucoma treatments.

Trabectome (NeoMedix) is a high frequency electrocautery device inserted through a corneal incision into the angle guided by gonioscopy to un-roof 90 to 120 degrees of Schlemm’s canal, exposing the posterior canal wall and collector channels. It is often combined with cataract surgery in mild to moderate open-angle glaucoma. An early study saw a mean 41 per cent reduction in intraocular pressure (IOP) at 18 months with few complications.

Gonioscopy-assisted transluminal trabeculotomy (GATT) is an ab interno procedure performed with a suture or illuminated catheter inserted into Schlemm’s canal up to 360 degrees. The TM is torn off with the suture or catheter, leaving the posterior wall of Schlemm's canal and collector channels exposed. It is useful in several different types of glaucoma in adults and children, and in patients with prior surgery, Dr Smith said.

Studies show GATT reduces mean IOP by 33 to 55 per cent, and medications from three before surgery to about one after 18 months. Complication rates are low, but at 24 months failure rates run as high as 60 per cent in patients with prior cataract extraction.

iStent (Glaukos) is a TM bypass device indicated for use with cataract surgery in adults with mild to moderate open-angle glaucoma treated with medication. It is inserted into Schlemm’s canal during cataract surgery, allowing fluid to flow directly to collector channels.

At 24 months, in a study with one shunt implanted, it lowers IOP more than cataract surgery alone, with 53 per cent reduced 20 per cent or more compared with 44 per cent for cataract surgery alone. Complication rates are low, but its IOP reduction effect fades over time.

Hydrus (Ivantis) is a microstent in phase 3 clinical trials. It is inserted into Schlemm’s canal, scaffolding and dilating the canal for three clock hours. At 24 months it lowers IOP by 20 per cent or more in 86 per cent of patients, compared with 45 per cent with cataract extraction alone. Complication rates are low, and IOP reduction effect does not appear to fade as much as some other approaches.

“Angle surgery is here to stay, so overcome the learning curve and get comfortable in the angle,” Dr Smith concluded.

Oluwatosin U Smith: Tsmith@glaucomaassociates.com