Clinical FeaturesOphthalmology

Recent advances in glaucoma management provide hope to thousands of sufferers

Glaucoma is the most common cause of irreversible blindness worldwide. Open-angle glaucoma (OAG) is the most frequent phenotype, with a prevalence of 2% in people over the age of 40 years. The Irish College of Ophthalmologists have also identified glaucoma as the leading cause of blindness in Ireland, with the incidence expected to rise by 33% over the next 10 years. Almost half of all cases remain undiagnosed, as patients are often asymptomatic until much later in the disease course. This makes early detection and treatment imperative to a good visual prognosis. Glaucoma is characterised by progressive loss of retinal ganglion cell (RGCs) and optic nerve damage, often associated with elevated intraocular pressure (IOP). As a result, patients begin to lose their peripheral vision, and as the disease progresses their central vision can begin to be impacted; eventually leading to total loss of sight.

Over the past two decades there has been a proliferation of glaucoma treatments, with laser and minimally-invasive options bridging the gap between medical therapies and more traditional surgical interventions including trabeculectomy and aqueousshunt surgery. As a result, there has been a monumental shift in the glaucoma treatment paradigm from ‘drops for life and surgery as a last resort’ to ‘earlier intervention in order to preserve vision.’ Whilst trabeculectomy and aqueous-shunt surgery remain highly effective at lowering IOP, they come with higher complication risks including bleb infection, post-operative manipulation, revision surgery and hypotony. On the other hand, topical medications may not be effective enough at lowering the IOP, and their chronic use may give arise to non-compliance as well as aggravate ocular surface disease, thus exacerbating the very problem they were designed to address. The advent of laserbased glaucoma interventions as well as minimally invasive glaucoma surgery (MIGS) enables glaucoma specialists to narrow the gap between traditional treatment techniques.

Selective laser trabeculoplasty (SLT) was first introduced in 1995 and received US FDA clearance in 2001. It has been shown to reduce IOP by inducing a mild sub-clinical inflammatory reaction to the trabecular meshwork (internal drainage system of the eye), enhancing aqueous outflow, and is performed as a single, painless outpatient procedure with a short recovery time and a good safety profile. In 2019, the landmark Laser in Glaucoma and ocular HyperTension (LiGHT) RCT study was published. In this work, treatment naïve patients with ocular hypertension and open angle glaucoma were randomly assigned to topical anti-glaucoma medication vs SLT as their first-line treatment. At 36 months, 75% of the patients in the SLT group required no drops to maintain target IOP. The SLT group had overall better IOP control with a greater preservation of visual fields. First-line SLT at diagnosis has now been recommended as the preferred treatment by the UK National Institute of Care Excellence (NICE), and as an equivalent alternative to topical medication in the latest European Glaucoma Society Treatment Guidelines. If initially ineffective, SLT can be repeated, reducing the reliance on topical medications and the side-effects that can be associated with their use.

Minimally Invasive Glaucoma Surgery (MIGS) procedures are a heterogenous group of implants, devices and surgical techniques that tend to be simpler, safer and quicker to perform, albeit with a lower drop in IOP compared trabeculectomy and aqueousshunt surgery. They are therefore more suitable for mild-to-moderate glaucoma patients and can be performed in conjunction with cataract surgery or alone. There is increasing published outcome data supporting MIGS in lowering IOP and reducing the need for topical medication, improving the ocular surface, enhancing patient’s quality of life as well as reducing the rate of visual field progression and delaying the need for more invasive filtration surgery.

The mechanisms by which MIGS lower IOP include: trabecular bypass stents into Schlemm’s canal, overriding the resistance at the level of the trabecular meshwork (iStent, GlaukosCalifornia, USA and Hydrus, Alcon – Geneva, Switzerland), increasing uveoscleral outflow via drainage into the suprachoroidal space (Miniject, iStar Medical – Waver, Belgium and iStent Supra Glaukos – California, USA), visco-dissection of Schlemm’s canal and the outflow channels (OMNI device, Sight Sciences – California, USA and iTrack Advance, Nova Eye MedicalAdelaide, Australia) and excision of the trabecular meshwork (Kahook Dual Blade, New Medical World – California, USA and Sion, Sight Sciences – California, USA). Each MIGS procedure has its own place, with the choice of which MIGS to perform based on several factors including: surgeon experience, the type of glaucoma, the severity of glaucoma and rate of progression, medication burden, the target IOP as well as the presence of cataract.

With the advent of selective laser trabeculoplasty and minimally invasive glaucoma surgery, glaucoma specialists are equipped with a greater armetarium of IOP lowering treatments. This will allow patients a greater choice in their management, minimising the long-term use of topical medication. It is an exciting time to be a glaucoma surgeon and I personally have seen some very successful outcomes from the use of these newer treatments, which ultimately have led to significant improvements in my patient’s outcomes and their quality of life.

Insertion of OMNI® Surgical System cannula through ~2 mm clear corneal incision (left); accessing Schlemm’s canal and insertion of the microcatheter (middle); withdrawing the cannula to perform trabeculotomy (right)

Written by Mr Pavi Agrawal, Consultant Ophthalmologist – Specialising in Cataract and Glaucoma, Mater Private Hospital Dublin

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