Elevated intraocular pressure is a known risk factor for the development and progression of glaucoma. Trabeculectomy was first described in the 1960s and is a form of guarded filtration surgery, designed to improve the outflow of aqueous from the eye. It is performed usually in cases where the medical management of intraocular pressure is suboptimal and clear structural/functional progression is occurring. This aqueous usually drains into the subconjunctival space, resulting in a characteristic bleb seen in such patients, and from there it is thought to drain into the aqueous veins or absorbed by surrounding vascular or perivascular conjunctival tissue.
Progressive disease in the following groups:
- Primary open angle glaucoma
- Pseudoexfoliation glaucoma
- Traumatic glaucoma
- Angle closure glaucoma
- Pediatric glaucoma (surgery should be performed by specialist pediatric glaucoma specialists in this instance)
To lower, and then stabilize the intraocular pressure, thereby slowing glaucoma progression.
Where possible, a complete ophthalmic assessment should be performed before trabeculectomy surgery. This should include:
- Measurement of visual acuity
- A pupil examination
- An external eye examination including assessment of the eyelids
- Assessment of the intraocular pressure and gonioscopic visualization of the angles
- An ocular surface and intraocular examination (preferably utilizing a slit-lamp microscope)
- A dilated examination of the retina and optic disc
- Assessment of the degree of visual field loss and optic nerve damage (ideally, longitudinal visual field and imaging data should be available, demonstrating structural and functional deterioration)
- Documentation of previous ocular surgery or the presence of cataract
Types of anesthesia
Trabeculectomy filtration surgery should be performed either under sub-Tenon’s or peribulbar local (block) anesthesia. Alternatively, in some cases, a General Anesthetic should be considered(GA). The exact mode of anesthesia should be discussed with the patient beforehand, and anesthetist also involved if possible. Furthermore, the addition of sedative agents may be considered when a local anesthetic is administered.
Risks of surgery
Due to advances in technology, instrumentation and technique, the success rate following trabeculectomy surgery has improved steadily. The use of anti-fibrotics such as 5-Fluorouracil (5-FU) and Mitomycin-C (MMC) in particular has increased the success rate, but these should be handled with care. A recent multicentre study in Caucasian eyes found that a post-operative IOP below 21 mmHg or 20% reduction in IOP without medication was achieved in around 80% of patients. Documented risks include hypotony (6% within the first 3 months), bleb leaks (15-20%), surgical failure with the requirement for repeat surgery (20%), cataract and endophthalmitis (1 in 1000).
Patients should be warned that suture manipulation is common in the immediate post-operative period, and that the vision is likely to be blurred and potentially fluctuate during this time. Furthermore, they may require additional subconjunctival injections of dexamethasone and/or 5-Fluorouracil to abrogate the ocular fibrotic response. These risks are, however, likely to vary amongst different populations.
An eye pad and shield should be placed immediately after surgery. Typically patients should be followed up by the operating surgeon on day 1 after the operation, and then again at weekly intervals for the next 3 weeks. Depending upon the clinical course, the surgeon may elect to lengthen the intervals between patient visits thereafter.
- Trabeculectomy in the 21st century: a multicentre analysis. Kirwan JF, Lockwood AJ, Shah P, Macleod A, Broadway DC, King AJ, McNaught AI, Agrawal P; Trabeculectomy Outcomes Group Audit Study Group. Ophthalmology. 2013 Dec;120(12):2532-9.
- Trabeculectomy for normal tension glaucoma: outcomes using the Moorfields Safer Surgery technique. Jayaram H, Strouthidis NG, Kamal DS. Br J Ophthalmol. 2015 Jul 21.
- The singapore 5-Fluorouracil trabeculectomy study: effects on intraocular pressure control and disease progression at 3 years. Wong TT, Khaw PT, Aung T, Foster PJ, Htoon HM, Oen FT, Gazzard G, Husain R, Devereux JG, Minassian D, Tan SB, Chew PT, Seah SK. Ophthalmology. 2009 Feb;116(2):175-84.