CATARACT SURGERY IN GLAUCOMA

While modern cataract surgery is widely recognised as being one of the safest and most effective surgical procedures available, there is growing recognition that removing a cataractous lens might also be a beneficial intervention for patients with glaucoma. The issue, however, remains controversial and there is far from universal recognition of if and when cataract removal should be performed in patients with co-existing glaucoma. At the 2011 World Glaucoma Congress, two leading glaucoma experts presented the arguments for and against the contention that cataract surgery is the best operation for glaucoma. 'Cataract surgery is unquestionably the best glaucoma operation currently available,' Reay h Brown MD told delegates. his counterpart in the debate, Carlo E Traverso MD, said that while he believed that cataract surgery might be beneficial in certain specific glaucoma cases, it was nevertheless prudent to recall that 'all that glitters is not gold'.

Open-angle glaucoma Outlining the case for cataract surgery in glaucoma, Dr Brown, in private practice in Atlanta, Georgia, Us, said that he considered it 'a very good operation for open-angle glaucoma (OAG) and a great operation for angleclosure glaucoma'. The clincher, he said, is the fact that cataract surgery offers a far more convincing risk-benefit profile than any other glaucoma intervention. 'The problem with glaucoma surgery, as we all know, is risk, and this is what we are trying to avoid. Looking at the glaucoma surgery risks in the tube versus trabeculectomy (TVT) study, we see that complications occurred in 39 per cent of tube eyes and 60 per cent of trabeculectomy eyes after three years. The need for reoperation or loss of two or more lines of vision occurred in 22 per cent of tube eyes and 27 per cent of trabeculectomy eyes. Furthermore, there was failure at the end of three years in 15 per cent of the tube eyes and 31 per cent of the trabeculectomy eyes, which goes up to 33 per cent failure for tube and 50 per cent for trabeculectomy in the five-year data,' he said.

By contrast, cataract surgery both improves vision and has a very minimal risk of complications, said Dr Brown, adding that many studies show that cataract surgery lowers intraocular pressure (iOP). he cited one such study, the istent (Glaukos inc.) FDA trial, which compared cataract surgery plus istent implantation to cataract surgery alone.'Cataract surgery alone lowered pressure at 12 months by 8.4 mmhg while cataract surgery plus istent insertion lowered iOP by 8.5 mmhg. Another study by Poley, Lindstrom and samuelson also concluded that phacoemulsification by itself lowered intraocular pressure almost as effectively as any other glaucoma procedure,' he said. Cataract surgery is also beneficial in angle-closure glaucoma, said Dr Brown. 'This study of 83 patients from my own practice showed an average reduction in pressure of 3.3 mmhg and the overall reduction was 19 per cent. But if we stratify by preoperative pressure, we find the reduction is even greater. There were 19 patients with iOPs of 20 mmhg or above and the average was reduced from 22.3 mmhg to 17.1 mmhg, a reduction of 5.2 mmhg or 23 per cent. Anti-glaucoma medications also were reduced, so the true reduction was probably more in the range of 6 or 7 mmhg,' he said.

Conclusive evidence Outlining the case against cataract surgery being the best glaucoma operation, Dr Traverso, director of the Eye Clinic at the University of Genova, italy, said that clinicians should not rush to judgment on the issue until more conclusive evidence is brought to bear. Most of the cited POAG studies used only a single preoperative iOP, were retrospective, and did not include untreated patients. 'While some studies have indeed shown primary open angle glaucoma patients with higher preoperative iOP obtaining greater average reduction after phacoemulsification, most of the reduction can be explained by what statisticians refer to as regression to the mean,' he said. Dr Traverso said that the story is very different for angle closure glaucoma and that while phacoemulsification may indeed be helpful as a pressure-lowering measure for angle-closure patients, there is little convincing evidence to suggest the same for POAG patients. 'in primary angle closure, lens extraction seems to have a beneficial effect on iOP control and it is especially indicated in more advanced cases. interestingly there was also some evidence in the literature that iOP reduction was proportional to the degree of angle closure,' he said. Dr Traverso warned, however, that cataract surgery is more difficult to perform in patients with glaucoma, especially those patients with small pupils, exfoliation syndrome, poor mydriasis and weak zonules. in his view, the best procedure depends on a number of factors, including the surgeon's experience, the available technology, the patient's willingness to undergo the procedure, and a host of clinical factors.

'We must remember that glaucomas are not all the same. We need individual care for individual patients, and surgery tailored to the needs of the individual. While phacoemulsification techniques have greatly improved glaucoma management, clear lens extraction is indicated only in selected cases of primary angle closure glaucoma. safe small-pupil phacoemulsification requires specific skills and phaco can decrease bleb function and increase permanently the iOP in eyes with functioning filtering blebs. There is currently no evidence of any quality to suggest that lens extraction routinely represents a clinically useful and generally applicable treatment for POAG,' he concluded.