THERAPEUTIC FORUM

Watch for Bleb Infection Following
Trabeculectomy

by Christopher J. Quinn, O.D.

A 68-year-old black female has a two-day history of increasing redness, tearing and mild photophobia in her right eye. Her previous ocular history is significant in that she underwent combined cataract extraction and trabeculectomy O.U. three years before.

Best corrected acuity is 20/40 O.D., 20/25 O.S. Pupils are reactive with no afferent pupillary defect. Slit lamp examination of the right eye demonstrates intense conjunctival injection with a superior filtering bleb. The injection increases in intensity except for an area of white avascular conjunctiva adjacent to the limbus. The A/C has 2+ cell and flare. Applanation tonometry is 4mm Hg in the right eye and 12mm Hg in the left eye. There is no visible wound leak. The vitreous is clear with no change in the optic nerve. The vessels and periphery appear normal.

Infected filtering bleb in a patient with a history of cataract and trabeculectomy.

Diagnosis.
 Whenever you examine a patient who has had trabeculectomy surgery, an acute red eye may be the first sign that the filtering bleb is infected.

This patient is, in fact, experiencing blebitis. Infections of the filtering bleb occur when pathogenic bacteria invade and replicate within the bleb and the adjacent conjunctiva. Clinical characteristics are increasing redness, a loss of translucency of the bleb and occasional purulent exudate. Often the bleb appears thickened, and occasionally the bleb wall leaks. Patients report increasing conjunctival injection, foreign body sensation, occasional pain and photophobia.

Bleb infections are more common today because of the increased use of mitomycin as an antimetabolite in trabeculectomy surgery. Mitomycin prevents scarring of the filtering bleb. But it also often obliterates the vascular supply of the overlying conjunctiva, making the tissue more prone to surface infection. Infected blebs associated with mitomycin demonstrate a clearly identified pattern of conjunctival injections surrounding the area where the mitomycin-soaked sponge touched the conjunctiva. This results in a sharply demarcated avascular area of conjunctiva that does not become injected when inflamed. In bleb infections that are not caused by mitomycin, the conjunctiva becomes injected throughout the entire infected area.

The most significant danger with blebitis is that the infection could spread intraocularly. Because the trabeculectomy site creates an open fistula, bacteria from the infected bleb can migrate into the anterior chamber and result in endophthalmitis. A bleb-related endophthalmitis is a serious ocular emergency and requires immediate and aggressive treatment.

Treatment options.
Suspect bleb infection whenever a patient who has had surgical trabeculectomy complains of increasing conjunctival redness, foreign body sensation or photophobia. Prompt evaluation within 24 hours leads to early diagnosis to avoid the spread of infection inside of the eye.

The first choice of treatment is topical fluoroquinolones. The appropriate loading dose is one drop every 15 minutes for the first six hours, then one drop every 30 minutes for the next six hours afterward, with continuation of the drops hourly after 12 hours.

If the patient shows intraocular extension, indicated by an increase in the anterior chamber reaction and/or hypopyon formation, manage more aggressively. Treat with topically applied fortified antibiotics besides fluoroquinolones. Alternating a fortified cephazolin solution hourly with the fluoroquinolone is most beneficial.

In patients with resistant infections, or where the infection has spread and created an endophthalmitis, the treatments of choice are anterior chamber cultures and intraocular antibiotics in addition to topically applied antibiotics.

In all cases of bleb-related infections, you may start topical steroids after you observe the patient's initial response to antibiotic therapy. Topical steroids reduce the associated inflammation with a bleb infection and may improve the chance for salvaging a functional bleb following the resolution of the infection.