Trabeculectomy

During Trabeculectomy ('trab' surgery for short) a piece of drainage material is removed from the trabecular meshwork of the eye in order to create an opening. The new opening allows aqueous humor to flow more freely from the eye and under the conjunctiva, thus bypassing blockages and allowing a reduction in intraocular pressure. In order to cover the opening where part of the drain has been removed, a flap of tissue from the Sclera (the outermost white tissue surrounding the eye) is used. A variety of techniques during and after trab surgery are employed to properly modulate aqueous drainage to sufficiently lower pressure while preventing hypotony (too low pressures). Additionally, antifibrotic agents are used to help prevent scarring and preserve the patency of the fistula.

The aqueus fluid flowing through the new drainage opening forms a slight bubble against the covering scleral tissue. This bubble is referred to as a bleb. The edge of the bleb is located near the iris. The doctor will examine the bleb after surgery to determine that fluid is draining properly from it. View a short video here of the trab surgery (starting at about 2:44 minutes) Glaucoma Surgery.

Filtration Surgery Pre and post Operative Info

Trab surgery has been traditionally performed under monitored anesthesia employing retrobulbar or peribulbar block. However, due to risks with these blocks, topical anesthesia and light sedation are now more commonly employed. If a patient is not able to cooperate during the procedure, general anesthesia is used. The patient does not usually need to be admitted, but in some cases, a hospital stay is recommended. Topical corticosteroids are often administered a few days prior to the procedure to help prevent inflammation.

Following surgery, glaucoma medications are usually discontinued and topical antibiotics are used to safeguard against infection. A shield is used to cover the eye until the anesthesia has worn off. Patients are instructed to call immediately for pain that cannot be controlled with over the counter pain medication or if vision decreases, to not rub the eye, and to wear the shield at night for several days after surgery.Topical steroids are usually used for 6 weeks postoperatively to prevent scarring. The duration depends on the level of inflammation in the bleb as seen through the slit lamp and the presence of risk factors for failure. 

Risks and post operative challenges

• There are a number of problems which can occur with the bleb. Among these are flat bleb, bleb leak, and blebitis. 
• Suprachoroidal hemorrhage – This can occur several days after the procedure and involves a rupture of the ciliary artery which can result in pain and choroidal detachment.
• Hypotony - This is an occurrence of pressures which go too low and can threaten eye structures such as the retina.
• Cataract formation
• Encapsulated bleb -  This can lead to elevation of intraocular pressure. A technique known as needling is sometimes used, but opinion is split on whether this is more effective than other means to lower pressure.

Conclusion

Trabeculectomy is the most common type of glaucoma surgery for advanced glaucoma where medications or other interventions fail and where getting pressures even lower are desirable to preserve the optic nerve. There are several possible side effects, and a rather lengthy recovery period. However, there are newer techniques now available like the mini shunt, Canaloplasty, and others on the horizon.