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Trabeculectomy and antimetabolites
  1. S Fraser
  1. Correspondence to: Mr Scott Fraser Sunderland Eye Infirmary, Queen Alexandra Road, Sunderland SR2 9HP, UK; sfraser100totalise.co.uk

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Perfecting a technique that works takes practice, but it is getting increasingly hard to get this practice

When von Graefe first introduced iridectomy as a treatment for glaucoma, some practitioners noted that the patients who usually had persistent reductions in intraocular pressure (IOP) were those who developed an inadvertent filtering bleb at the site of the surgery. This led De Wecker,1 in 1882, to suggest that the IOP could be reduced by purposely creating a fistula between the anterior chamber and the subconjunctival tissues. He was the first to use the term “filtering” to describe this egress of fluid from the eye.2

Full thickness filtering procedures were used throughout the early 20th century but were bedevilled by a high rate of postoperative complications such as hypotony, flat anterior chambers, and suprachoroidal haemorrhage. For this reason, in the 1960s, a guarded filtration technique was developed and (incorrectly) named trabeculectomy.3,4 It is a tribute to this operation that it has, with certain modifications, persisted to the present day.

However, just as full thickness filtering procedures were compromised by excessive drainage, the enemy with guarded drainage procedures has been excessive scarring with subsequent reduction or abolition of aqueous flow from the eye into the subconjunctival space. It is now well recognised that in some situations this risk of failure secondary to scarring is greater. These include those aged under 40, those of African-Caribbean descent, and those with previous ocular inflammation including that induced by surgery and topical medications.

This scarring response has long been known to compromise filtration surgery—many of the advocates of de Wecker’s “filtering cicatrices” were disappointed that the lowering of the IOP rarely lasted more than 1 year.2 But it is only relatively recently that we have been able to modify this healing response with the use of the antimetabolites 5-fluorouracil (5-FU) and mitomycin C (MMC).5,6

The paper by Siriwardena et al, in this issue of BJO (p 873), indicates how important a tool these antimetabolites have become, with 82% of UK consultants who responded to their survey stating that they used them. What is perhaps more surprising is that only 9% used antimetabolites in more than half their cases. Similarly only 2% (that is, less than 20) of UK consultants used MMC in more than half their cases. Although this survey reflects practice in 1999 it appears that this figure is substantially lower than those for the United States and Japan.

Trabeculectomy will become a subspecialist procedure performed by those who have completed a recognised period of training in glaucoma and who perform a minimum number of trabeculectomies per annum

This discrepancy may well reflect differences in case mix between different countries—especially in the United States with a much higher black population. It may also reflect a more conservative approach in the United Kingdom. The complications of antimetabolite use are well known, including cataract, prolonged hypotony, epitheliopathy, blebitis, and endophthalmitis.7,8 Trabeculectomy is usually performed on eyes with normal visual acuity and vision threatening results are devastating to even the most fully informed patient.

As all ophthalmologists know, filtration surgery represents a delicate balance between maintaining the integrity of the eye and prevention of excess scarring. Although, like all surgery there is an element we cannot control, the key to successful surgery is to perfect a technique that allows as much control over the eye as possible. This involves preoperative assessments of risks (for example, reducing conjunctival inflammation with steroids), a meticulous intraoperative technique (for example, use of antimetabolites, releasable sutures), and timely and appropriate postoperative interventions (for example, subconjunctival 5-FU, bleb needling). It is consideration of these factors that allows us to sit within the therapeutic window that produces a sighted eye with an appropriate level of intraocular pressure.

Perfecting a technique that works takes practice—surgeons who do more of a particular type of operation tend to get better results.9 It is, however, getting increasingly hard to get this practice. The number of trabeculectomies performed in the United Kingdom has declined over the past 5 years.10,11 There may be a number of reasons for this, including a wider range of medical treatments, earlier diagnosis, or perhaps a reduction in the number of redo trabeculectomies because of the use of antimetabolites. Because of this, ophthalmology trainees are now less likely to be exposed to filtration surgery and at the end of their higher specialist training in ophthalmology (www.rcophth.ac.uk/education/curriculum_hst_ophth.html) are unlikely to be fully competent in the procedure.

It is inevitable that, with fewer trabeculectomies being performed, patients are on topical treatments for longer. Because of the effects of topical medications on the conjunctiva it is likely that, in those patients coming to filtering surgery, antimetabolites will more often be used, making the surgery less forgiving. With the added pressure of increased public scrutiny of doctors and a generally more aware patient group it would appear inevitable, whether we like it or not, that trabeculectomy will become a subspecialist procedure performed by those who have completed a recognised period of training in glaucoma and who perform a minimum number of trabeculectomies per annum.

Note in Proof

Perfecting a technique that works takes practice, but it is getting increasingly hard to get this practice

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