The bleb may fail following filtering surgery. In eyes with failing blebs, reduced bleb height, increased bleb-wall thickness, vascularization of the bleb, loss of conjunctival microcysts, and increased IOP may be seen. Risk factors for bleb failure include anterior segment neovascularization, black race, aphakia, prior failed filtering procedures, uveitis, prior cataract surgery, and young age. Initial management of failing blebs often includes digital massage. In eyes that do not respond to this initial therapy, transconjunctival needle revision may restore aqueous flow.

The use of contact lenses with a filtering bleb presents special problems. Contact lenses may be difficult to fit in the presence of a filtering bleb, or the lens may ride against the bleb, causing discomfort and increasing the risk of infection. Several options can be considered for the patient who has myopia, needs a trabeculectomy, and prefers not to or cannot wear spectacles. Refractive surgery options include photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), or intracorneal ring segments prior to trabeculectomy. Clear lens extraction (either before, after, or combined with trabeculectomy) is controversial. In some circumstances, hard or soft contact lens use under close supervision may be considered after trabeculectomy. Contact lens use is more often feasible in patients after implantation of a glaucoma drainage device than after trabeculectomy. When an initial filtering procedure is not adequate to control the glaucoma and resumption of medical therapy is not successful, revision of original surgery, a second filtering surgery at a new site, glaucoma drainage device implantation, or possibly cyclodestructive procedures may be indicated.

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hypotonous eyes after glaucoma filtering surgery. Br J Ophthalmol. 2004;88(1):99–103.

Combined Cataract and Filtering Surgery

Both cataract and glaucoma are conditions that show increasing prevalence with aging. It is not surprising that many patients with glaucoma eventually develop cataracts either naturally or as a result of the effects of glaucoma therapy. It should also be noted that cataract surgery alone may lower IOP in eyes with open angles and may lower it even more in eyes with phacomorphic narrow angles.

Indications

Cataract surgery may be combined with trabeculectomy in the following situations:

cataract requiring extraction in a glaucoma patient who has advanced cupping and visual field loss

cataract requiring extraction in a glaucoma patient who requires medications to control IOP but who tolerates medical therapy poorly or has inadequately controlled IOP

cataract requiring extraction in a glaucoma patient who requires multiple medications to control IOP

The success of IOP control in combined surgery is reduced compared to that in trabeculectomy alone. Thus, in uncontrolled glaucoma, combined surgery is usually performed only in specific circumstances, such as primary angle-closure glaucoma uncontrolled with medications or after laser iridotomy when cataract surgery alone is unlikely to provide successful IOP control. Many surgeons perform trabeculectomy with cataract surgery when the IOP is stable but the patient is using 2 to 3 IOP-lowering medications. The goal in these cases is to avoid perioperative problems with elevated IOP and to achieve a long-term reduction in the number of medications required. However, many surgeons would perform cataract surgery alone in a patient who has controlled IOP using 1 medication, with mild to moderate cupping and little visual field loss.

Relative contraindications

Combined cataract and filtering surgery should be avoided in the following situations, in which glaucoma surgery alone is preferred:

glaucoma that requires a very low target IOP

advanced glaucoma with uncontrolled IOP and immediate need for successful reduction of IOP

Considerations

A combined procedure may prevent a postoperative rise in IOP. Combined procedures are generally less effective than filtering procedures alone in controlling IOP over time, although combined procedures that use small-incision phacoemulsification techniques with an antifibrotic agent appear to have better success rates than trabeculectomy combined with extracapsular cataract surgery. For patients in whom glaucoma is the greatest immediate threat to vision, filtering surgery alone is usually performed first.

Several clinical challenges are common in patients with coexisting cataract and glaucoma. Medical therapy for glaucoma may create chronic miosis, and the surgeon must deal with a small pupil. In patients with exfoliation syndrome, zonular support of the lens is often fragile, and vitreous loss is therefore more common in such complicated eyes. As with all surgery, the risks, benefits, and alternatives should be discussed with the patient.

Technique

Long-term control of IOP is better with combined glaucoma and cataract operations than with cataract surgery alone, and several surgical approaches to coexisting cataract and glaucoma are currently used. Although little evidence exists to compare the long-term outcomes of patients treated with these different approaches, it is reasonable for the surgeon to use the cataract procedure that he or she performs best, because the primary indication for surgery is the presence of cataract.

Trabeculectomy may be combined with phacoemulsification, which is performed through the superior trabeculectomy incision or through a temporal clear corneal incision. Also, cataract extraction may be combined with implantation of a glaucoma drainage device. In addition, there are several procedures that combine cataract surgery with surgery on the Schlemm canal, as for example, canaloplasty (see the section Nonpenetrating Glaucoma Surgery) and trabectome. In trabectome, electroablation of the trabecular meshwork is performed through a temporal corneal incision, a technique similar to that used in goniotomy, to lower IOP in OAG.

For the patient whose IOP is controlled medically, clear corneal cataract surgery alone may be the appropriate choice. As no violation of conjunctiva or sclera occurs with this procedure, there is little reason to perform an incidental trabeculectomy. Rather, standard trabeculectomy can be performed when dictated by independent indications.