ABiC Blog

06 August 2018

With All the Options We Have to Enhance Outflow, It’s a Great Time To Be a Plumber (Part 1)

I can still remember the afternoon when I, a senior resident fascinated by technology, approached my long-time mentor and informed him that I had decided to apply for a fellowship in glaucoma. I recall how he looked up from his seated position with his steel gray-blue eyes and intimidating stare. I remember his exact words that he delivered with a shocked, dismayed, and disappointed voice: “Why on earth would you want to be a plumber?”.

You see, this faculty member, one of the brightest and most knowledgeable individuals I’ve had the pleasure to work with, was a cornea specialist.  And during my time as a resident, the major focus of my academic endeavors was in cornea and anterior segment.  I was to be his protégé and glaucoma, at that time, simply was not “sexy”.

Now, ten years later, glaucoma has become a very sought-after field in ophthalmology.  More residents are considering doing glaucoma fellowships. And surgeons who would have never fathomed touching a glaucoma device are now attending symposium after symposium to learn how incorporate glaucoma surgery into their practice.  What has changed?  Why the new interest?  Simply put, micro-invasive glaucoma surgeries (MIGS) have transformed the landscape of ophthalmology.  Once met with skepticism, MIGS have become a well-established method for addressing glaucoma, especially when concomitantly managing a visually significant cataract.

Trabecular micro-bypass using the iStent (Glaukos) was approved by the Food and Drug Administration in 2012. Since then, we have seen an innovation explosion in MIGS devices. Today we have the means to reduce aqueous production by delicately altering ciliary body function with endoscopic cyclophotocoagulation or using the newly developed G6 micropulse laser (Neomedix).  We also have a myriad of tools to enhance aqueous filtration. These new tools can fit into three broad categories based on their general area of action. First, there are those that enhance outflow through the conventional outflow system and can assist outflow by altering this system at the level of the trabecular meshwork or beyond (Table 1).  Then there are devices that facilitate outflow through the suprachoroidal space (CyPass Supraciliary shunt and iStent Supra), as well as those devices that divert aqueous into the subconjunctival space (Xen45 gel implant).

With all these devices and procedures, determining which procedure to apply to each specific individual clinical scenario can be perplexing. I am routinely asked how I decide which device or procedure to use, and what factors help determine which procedure to perform.  Surgeons new to the MIGS realm want to know if an algorithm exists or if I simply limit my use of devices to one or two. Unfortunately, there is not a straightforward or simple answer.  But, I do feel all devices are useful and necessary in our continued effort to battle glaucoma: each device provides its own unique means to reduce a patient’s IOP and/or medication burden.  There are many factors that help me determine which procedure will be used. I am the first to confess that what I do is more anecdotal than truly scientific, since we do not have prospective, randomized, comparative studies evaluating the efficacy of each procedure in various clinical settings.  In general, I look at a patient’s stage in the disease process and the type of glaucoma, the patient’s measured IOP coupled with their target IOP range, the number of glaucoma medications and the appearance of the drainage angle.  I also look at the patient’s crystalline lens to determine if concomitant cataract surgery is indicated.

In the presence of a visually significant cataract I ask the following: am I taking the patient to surgery because they have a cataract and I’m simply adding a MIGS procedure to reduce a patient’s medication burden? Or, am I taking the patient into surgery because they need glaucoma surgery and I’m coupling the procedure with cataract extraction because they happen to have a cataract? Despite being a tertiary glaucoma referral center, in my center most patients fit into the former category. The same holds true for my colleagues who have comprehensive practices. MIGS are offered to all patients undergoing cataract extraction to reduce their medication burden.  We are driven to decrease the patient’s dependence on topical medications for a multitude of reasons: to improve compliance, skyrocketing costs of medications, to eliminate the drug-related adverse effects, and to offer improved quality of life.

But we must pause and understand the risk-to-benefit ratio for each MIGS procedure, as they all have their own safety profile.  Eliminating or reducing the need for topical glaucoma medications is of great benefit, but it can be overshadowed if their “cataract surgery” has a prolonged or complicated recovery period.  Patients are familiar with cataract surgery and expect excellent vision the minute their procedure is complete.   They have had friends, family members or neighbors that have had cataract surgery and remember how well they did after surgery.  I want patients to have a similar experience even whn they are having TWO procedures, and so I always try to add a MIGS procedure that adds little to the patient’s risk and recovery.  I don’t want to worry about hypotony, myopic shifts, and excessive blood in the anterior chamber or recurrent hyphemas.  The two procedures I like to use in this setting are trabecular micro-bypass using the iStent or transluminal viscodilation, also referred to as ab-interno Canaloplasty (ABiC) using the iTrack catheter (Ellex). These two procedures help facilitate outflow through the conventional outflow system without significantly damaging, removing, or altering the patient’s natural aqueous pump (as described by Murray Johnstone) or removing the blood aqueous barrier.

By maintaining the blood aqueous barrier, the risk for post-operative hyphema is limited in the immediate post-operative period and virtually eliminated in the long-term.  More importantly, because the procedures maintain the normal anatomy, the anatomy or the drainage angle can be further manipulated in the future – if necessary.  Patients can still have laser trabeculoplasty, for example.  They can still have other implantable devices that will soon come to market (iStent inject and iDose, Glaukos…., Hydrus micro-stent, Ivantis).  If necessary, we can still perform trabecular ablative procedures, either focal (goniotomy using the Kahook Dual Blade, New World Medical…, Trabeculotomy using the Trabectome) or global using the Trab360 device (Sight Sciences….) or by performing the GATT procedure using the iTrack catheter or prolene suture.   The less intervention/damage we “do” as a primary procedure, the better we are at setting ourselves up for success in the future.  This is my approach for patients with controlled, mild-to-moderate primary open-angle glaucoma on 1-4 medications with a relatively healthy angle.  My procedure of choice changes in patients with secondary open-angle glaucoma or those with dysgenic or diseased appearing angles, and will be discussed in future blogs.

Twenty percent of patients undergoing cataract surgery have glaucoma, and of these half are on 1-2 medications (Source: Ferguson et al).  Unlike in the past, entrance into the surgical theater to remove a cataract provides us with a golden opportunity to help these patients control their glaucoma with fewer medications, many of which can be maintained without medications for several years (Source: The Eye Diseases Prevalence Research Group).  We are now automatically addressing a patient’s glaucoma when we are managing their cataract, similar to the way we address stigmatism with advanced IOLs or arcuate incisions.  We owe it to our patients to offer them the opportunity to benefit from advanced technology glaucoma devices.  We can help improve a patient’s quality of life by eliminating or reducing the need to bathe the eye in toxic preservatives on a daily basis.  It sure is a good time to be a plumber.

References:

1. Ferguson TJ, Swan R, Sudhagoni R, Berdahl JP. Microbypass stent implantation with cataract extraction and endocyclophotocoagulation versus microbypass stent with cataract extraction for glaucoma. J Cataract Refract Surg. 2017 Mar;43(3):377-382. doi: 10.1016/j.jcrs.2016.12.020.

2.The Eye Diseases Prevalence Research Group, Arch Ophthalmology. 2004; Prevent Blindness America

View all blog posts
This website uses cookies to ensure you get the best experience on our website.
The cookies do not store any personalised information. Learn More