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Page 2 of 14 Komzak et al. Mini-invasive Surg 2021;5:13 I http://dx.doi.org/10.20517/2574-1225.2020.103

INTRODUCTION
Minimally invasive glaucoma surgery (MIGS) is an emerging field in open angle glaucoma (OAG)
management with a promise to offer a reduction in intra-ocular pressure (IOP) and medication burden
without the comparatively high risk of complications associated with more invasive incisional procedures.
Glaucoma is characterized by progressive optic neuropathy that is associated with progressive field loss in
which IOP is a key modifiable factor. Current established management options to reduce IOP primarily
revolve around topical medications or application of selective laser trabeculoplasty (SLT) or a combination
of both. Failing these, patients will often require invasive and complicated surgery to avoid blindness. In
recent years, however, MIGS has heralded a new dawn in reducing IOP for glaucoma patients.

Topical medications for glaucoma
The main aim of topical therapy is to reduce IOP and to do so with fewer medications and side effects as
[1]
possible (summarised below in Table 1 in order of treatment preference) . The first-line topical agents
in OAG are the prostaglandin analogues, which utilise the uveoscleral pathway to increase outflow of
aqueous humor and are usually taken as a single dose at night. These medications cause minimal systemic
adverse events, but local adverse events including conjunctival hyperaemia, periocular darkening, iris
darkening, eyelash darkening and lengthening, macular oedema, and uveitis are known to occur. Second-
line agents include b-adrenergic blockers, a-agonists, carbonic anhydrase inhibitors, and cholinergic
agonists, and are used when prostaglandin analogues are insufficient to control IOP or are contraindicated.
Many of these medications cause local and systemic side effects including ocular irritation and dry eye.
b-adrenergic blockers in particular are contraindicated in chronic obstructive pulmonary disease, asthma
[1]
and bradycardia due to their systemic effects .

Alternatives to topical medications
While medications can significantly reduce the disease progression of OAG with ideal use, they are
limited by inconsistent compliance and their associated side effect profile. Compliance can be affected by a
multiplicity of medications and long duration of treatment. A recent study of 128 South Australian patients
found that for patients on long-term topical glaucoma therapy, the maximal adherence level was as low as
[2]
41.4%. The primary reason for poor compliance was reported as poor memory or forgetfulness . For this
reason, medications are often inferior to surgical intervention as they require long-term compliance, and in
this case only an estimated 41.4% of patients are truly seeing the full effect of treatment, in comparison with
surgery where ongoing effect is not reliant on the patient’s ability to comply with the treatment regimen.

For severe OAG that is uncontrolled with medications, trabeculectomy is the most common IOP-lowering
surgery performed; however, it is an invasive procedure and carries a significant risk of complications.
A recent Cochrane review of five studies showed that complications are comparatively likely with
trabeculectomy. These include hyphaema (seen in 13.1% of eyes), shallow anterior chamber (14.1%),
choroidal detachment (14.1%), postoperative IOP spike (2.1%), anterior chamber inflammation (7.3%),
[3]
hypotony (15.6%) and accelerated cataract progression (13.7%) . An alternative to trabeculotomy is laser
trabeculoplasty, which is a less invasive in-office procedure that can lead to significant IOP reductions;
however, it is less effective than undergoing a trabeculectomy, with a 10% failure rate per year . In addition
[1]
to these methods, whilst cataract surgery is traditionally performed to treat vision distortion, it is also a
proven effective adjunct in the management of glaucoma. Phacoemulsification alone has been shown to
cause a mean reduction in IOP of 5.3 ± 3.9 mmHg and reduce mean medication burden from 1.7 ± 0.9 to
0.7 ± 0.9 at 24 months as a standalone procedure .
[4]

What is minimally invasive glaucoma surgery?
Given the limited success profile of current treatments, MIGS has become increasingly popular as a form of
treatment for glaucoma. There are numerous MIGS approaches, including: (1) increasing flow through the