Cataract Surgery in Patients with Functioning Filtering Blebs

The Problem of Cataract Formation after Glaucoma Surgery

Cataract formation is a common long-term event after glaucoma filtering surgery. Cataract formation may be accelerated by postoperative hypotony, flat or shallow anterior chamber, iridectomy, use of antimetabolites, repeated secondary interventions, or other factors. The incidence of cataract formation after filtering surgery also depends on the stage and progression of cataract before glaucoma surgery. Most patients with unilateral glaucoma surgery, even when uneventful, develop cataract earlier than in the unoperated contralateral eyes. The reason for this is still not fully understood. Hence, cataract operation after successful filtering surgery has long been an issue and its influence on long-term intraocular pressure (IOP) outcome must be taken into consideration, particularly as low IOPs are needed for visual field preservation.

The Influence of Various Glaucoma Procedures on Cataract Formation

Trabeculectomy is the procedure of choice to achieve low intraocular pressures. It is designed to reach a low target IOP without additional antiglaucoma medications. In a recent meta-analysis of randomized, prospective, controlled studies it was shown that penetrating filtering surgery results in significantly lower IOP than after nonpenetrating filtering surgery as well as other types of angle surgery.

The incidence and progression of cataract formation after penetrating versus nonpenetrating glaucoma surgery are also different. It has been clearly shown in randomized, prospective studies comparing trabeculectomy to nonpenetrating glaucoma surgery that cataract formation is significantly lower in nonpenetrating procedures. The possibility of cataract formation and subsequent surgery has to be taken into consideration when evaluating the long-term prognosis of glaucoma surgery, and this may have a significant influence on the decision to undertake filtering surgery, the sequence of both surgeries or the use of combined procedures.

Drainage devices have become more popular for complex or even for primary forms of glaucoma. The cataractogenic impact of drainage devices, however, has not yet been adequately investigated.

The Influence of Various Techniques of Cataract Extraction on the Survival of Filtering Blebs

Modern phacoemulsification surgery can produce a moderate but significant long-term IOP reduction in glaucoma patients.

It is not understood whether cataract surgery in eyes with previous trabeculectomy will induce an increase or decrease in IOP. It has been argued that wound healing processes after cataract surgery may have a major influence on the survival of previously functioning filtering blebs. Siriwardena et al. showed prolonged flare in the anterior chamber suggestive of delayed inflammation that could stimulate wound healing over a longer postoperative period. The size of the incision of cataract surgery and the vascularity of the surrounding tissue may have an influence of the tendency of the bleb to obliterate. Previously, when intracapsular or extracapsular techniques with nucleus expression were common, a large corneoscleral incision was needed and was disadvantageous to an existing functioning filtering bleb. Therefore, some surgeons preferred clear cornea incisions for extracapsular or intra­capsular cataract extraction that did not touch the conjunctiva, or they used corneoscleral incisions outside the filtering area, as routinely performed in combined simultaneous cataract–glaucoma surgery.

In modern cataract surgery with foldable lens implantation, a clear cornea incision is routinely used in glaucoma patients, mostly from the temporal side. This approach does not alter the conjunctiva and therefore is considered potentially safe in respect to scarring of a functional filtering bleb. However, despite these theoretical considerations, recent reports show a negative influence on the survival of patent filtering blebs even with this technique.