The future of glaucoma surgery

Advancing technology, ageing populations will likely mean more of both trabeculectomy and MIGS

Howard Larkin

Posted: Saturday, June 6, 2020

Leon Au BSc, MBBS, FRCOphth

Will minimally invasive glaucoma surgery (MIGS) replace trabeculectomy? The answer may be a partial “yes” – although increasingly severe and rapidly progressing disease in ageing populations may increase absolute trabeculectomy numbers, debaters argued at the ESCRS Glaucoma Day 2019 in Paris, France.

While trabeculectomy will likely remain the go-to procedure for the minority of patients with severe and/or rapidly progressing glaucoma, MIGS devices already have displaced filtration surgery in many milder cases, said Leon Au BSc, MBBS, FRCOphth, consultant ophthalmologist at Manchester Royal Hospital, UK.

MIGS procedures are more than adequate for the vast majority of glaucoma patients, and future, more effective MIGS will likely capture even more patients, Dr Au added. Where 20 years ago there were almost no treatment choices between maximum medication and invasive filtration surgery, today’s options range from SLT and other laser procedures to MIGS trabecular, supraciliary and subconjunctival stents, to canaloplasty and viscocanalostomy.

These less-invasive options fulfil patients’ desire to keep disease asymptomatic while minimising eye drops and invasive, uncomfortable, surgical interventions – not to mention reducing time off work and in hospital, Dr Au said.

In addition, few glaucoma patients actually need the sub-12mmHg intraocular pressure trabeculectomy can provide, and this largely comes down to disease severity and age, Dr Au said. “I’d hope to intervene earlier with less invasive procedures to avoid patients progressing to end-stage disease treated with one too many eye-drops”, said Dr Au.

Glaucoma is generally diagnosed late in life and progresses slowly or not at all, so moderate IOP reduction is enough to prevent visual disability in most patients.

For example, a large longitudinal study of open-angle glaucoma patients in the UK found mean age at diagnosis was more than 71 years, with 30% dead in 10 years, 44% in 15 years and 63% in 20 years. Average time from presentation to death was just over 7.5 years – not surprising given an overall UK life expectancy of 81 years, Dr Au pointed out (Sharma T, Salmon JF, Br J Ophthalmol. 2007 Oct; 91(10): 1282–1284. Shahid H, Salmon JF. Br J Ophthalmol. 2013 Feb;97(2):235-6. King C et al. Br J Ophthalmol. 2018 Dec;102(12):1663-1666).

As a result, “some of the new devices have managed to displace trabeculectomy”, Dr Au said. He cited a study at Manchester in which the iStent (Glaukos) implant proved sufficient for three-quarters of 16 trabeculectomy candidates, which included those on acetazolamide (Diamox) pre-op, or who had cup-to-disc ratios greater than 0.7, required more than two IOP drops, had IOP over 21.0mmHg and visual field mean deviation of -4.0dB or more. During seven years’ follow up, only four required trabeculectomy, sparing 12 patients the more invasive and riskier procedure (Ziael H, Au L. 8th World Glaucoma Conference, 2019, Melbourne, Australia).

“I think that displacement may be called replacement, and for me, the future of MIGS is very bright,” Dr Au said.

Age driving up trab need

Kuldev Singh MD, MPH

Arguing for the continuing need for trabeculectomy, Kuldev Singh MD, MPH, of Stanford University, California, USA, allowed that most glaucoma patients do not need the dramatic IOP reduction trabeculectomy affords and may need no surgery at all. He refers to these low-severity patients as having “glaucoma light”. Most of “glaucoma light” is treated pharmaceutically and only a small subset of patients with glaucoma currently undergo any surgery at all whether it be MIGS, trabeculectomy or something else.

While most glaucoma patients are slow progressors, the 3-to-5% who are fast or very fast progressors may need IOP levels that cannot be achieved with MIGS procedures and thus may benefit from trabeculectomy.

However, while rapid progressors are not frequent, they do sometimes require very low IOP and even slow progressors may need trabeculectomy if they live long lives after developing glaucoma. Most of the MIGS procedures have only been studied for one-to-three years and there exists decades-long follow-up with trabeculectomy to know that there is the potential for long-term success.

“There is that 5% where you need a really low pressure and there’s nothing that does it like a trab,” he said. So while MIGS will undoubtedly grow in numbers, and that is a good thing, it will not completely replace the need for trabeculectomy. The two classes of surgery can and should co-exist, he believes.

Large prospective trials, including the landmark Tube v Trab study, demonstrate that trabeculectomy can reliably reduce IOP to the low single digits for five years or more (Gedde SJ et al. AJO 2012;153(5):789-803). Other studies suggest a correlation between big drops in IOP and actual improvement in visual fields, Dr Singh added (Caprioli et al. Ophthalmology 2016;123:117-128).

“Six [mmHg] may be the new 12 for the very severely affected patients and/or those who continue to show progression with low double-digit IOPs. An IOP of 12mmHg is by no means a guarantee of visual preservation, especially when the optic nerve is severely damaged and there is very little reserve.

And while the average lifespan after glaucoma diagnosis was historically short, it is getting longer, Dr Singh noted. As more people age into their late 80s, 90s and even 100s, the incidence of rapidly progressing glaucoma is jumping, with Trabeculectomy is not only the most reliable procedure for long-term IOP reduction, it is also titratable and, when performed by an experienced surgeon with careful attention to follow-up, does not have to be associated with a high risk of complications, Dr Singh said. However, achieving good long-term results requires technical skill, knowledge of how to modulate wound healing and, most of all, time with patients during the perioperative period, Dr Singh said.

Already, Dr Singh is noticing that patients are travelling long distances to see him for trabeculectomy as the number of more recently trained surgeons have either not learned the procedure or have stopped doing it, and these are not mutually exclusive scenarios. In his opinion, those who were not adequately trained to perform trabeculectomy before beginning practice are ultimately more likely to abandon the procedure due to frustration with results.

“We will absolutely still need trabeculectomy in the future. If you want to call yourself a glaucoma specialist, learn trabeculectomy and how to follow those patients. This does not mean you cannot and should not also embrace MIGS – the choice of procedure should obviously be individualised based upon what each patient needs,” said Dr Singh.