CATARACT AND GLAUCOMA

In the ongoing discussion of whether to perform cataract surgery alone or in combination in glaucoma patients, a Canadian glaucoma specialist says the choice depends on the features of the disease in individual patients, but adds there is scientific evidence that supports some of the current options. In brief, cataract surgery alone can be considered for the patient who has ocular hypertension or early damage, but who has well-controlled intraocular pressure (IOP). And combined surgery can be the preferred choice if there is advanced damage or IOP is unlikely to reach targets with the modest IOP-lowering effects of cataract surgery alone, said Jamie Taylor MD, clinical assistant professor of ophthalmology at Canada’s University of Victoria. He spoke at the recent 5th World Glaucoma Congress where he gave an overview on cataract surgery in the glaucoma patient.

When it comes to patients with pseudoexfoliation who do not yet have glaucoma, several studies in the medical literature show there are mild pressurelowering effects with cataract removal. One study by Damji et al, from 2006, found that phacoemulsification alone produced greater IOP-lowering at two years in pseudoexfoliation patients than those without PEX, in both suspect and glaucoma populations. Degree of IOP lowering correlated positively with irrigation volume used.

Reducing bias

Another study, by Shingleton, from 2008, found a 1.0 to 2.0 mmHg reduction in IOP out to seven years in pseudoexfoliation patients without glaucoma. People needing glaucoma surgery were excluded. However, those pseudoexfoliation glaucoma suspects had a 17 per cent risk of IOP spike over 30.0 mmHg on the first day post surgery. Dr Taylor notes that a number of studies in the literature have methodological problems, but the Ocular Hypertension Treatment Study (OHTS) overcame some of that by including significant data on patients prior to cataract surgery, reducing bias from regression to the mean and medication impact.

OHTS results showed a significant IOP drop in patients who had cataracts removed, but no change in IOP in the controls who did not have cataracts removed. Plus, over time, pressure tended to increase gradually in the months after the surgery. The IOP-lowering effect was strongest in patients with higher IOP prior to surgery. Also, some patients actually had an increase in IOP. An increase can also happen in patients with uveitis and those with previous filtering surgery, he said. "Taking various studies into account, it appears we may be able to discontinue a medication early on after surgery, but three or four years later they’re back on their prostaglandin," Dr Taylor said.

As for performing cataract surgery as a glaucoma treatment, the evidence doesn't yet support that in the open-angle glaucoma population. There have been no randomised trials comparing surgery to medication in this group, he said. However, with the angle-closure population it’s been shown that cataract surgery alone can lead to substantially lower IOP. There are a number of prospective studies on this, Dr Taylor said.

Generally though, various guidelines, including those from the Canadian Ophthalmological Society, note there is a risk of an IOP spike with cataract surgery alone. As for other surgeries, the guidelines note that often trabeculectomy can worsen cataract, more so than medication alone. “And with the combined procedures, if you’re looking at someone with markedly elevated intraocular pressure, the combined procedure phacotrabeculectomy is a few millimetres of mercury less effective than trabeculectomy alone," he said. But the field is changing. In 2013, trabeculectomy rates are lower than before the introduction of prostaglandins. And there are improved glaucoma surgery options, including trabeculectomy with mitomycin C, minimally invasive glaucoma surgery such as trabectome, tube shunts, non-penetrating surgeries and more.

Key factors

A crucial factor, too, is where the patient is on the glaucoma (not cataract) disease spectrum. When choosing which surgery to perform, key factors to take into account include the degree of optic nerve damage, what the IOP target is, how many medications a patient is on and the surgeon's comfort and experience with specific procedures.

Individual patients should be treated according to the degree of severity of their disease. In early glaucoma where IOP is controlled with one or two medications, most guidelines recommend phaco alone. In advanced glaucoma, patients need a glaucoma procedure added, usually phacotrabeculectomy with MMC. In moderate or advanced glaucoma with a markedly elevated IOP, evidence suggests trabeculectomy MMC first, then phaco later.

It’s a rapidly evolving field and there are an ever increasing number of glaucoma surgery options. In the coming years, “the question of when and how to perform combined surgery will have a different answer,” Dr Taylor said.