ABiC Blog

06 August 2018

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

September 28, 1978: a day of infamy for glaucoma. A new drug that was to be milder on the eye and used earlier in the treatment paradigm to prevent blindness – a breakthrough in care – was announced during the CBS Evening News with Walter Cronkite. Cronkite’s opening statement read, “Glaucoma, a painful disease of the eye that can lead to blindness, is not curable. Drugs have been around for years, which can control the disease but often with such unpleasant side effects some patients found the control worse than the condition. There was an announcement in New York City today, which may end that dilemma for millions of Americans”. The drug was timolol maleate.

Even back then, we yearned for better options.  There was a dilemma for patients; treat an asymptomatic ailment with uncomfortable, sometimes debilitating medications, or lose vision to the silent thief of sight.  Though we’ve had several additions to our drug armamentarium, patients still suffer from adverse reactions to medical therapy.  Almost half of all treated patients suffer from some level of ocular surface disease, and incisional procedures certainly are not benign, especially bleb-creating filtration procedures.  Although useful, effective and needed, filtration procedures, especially trabeculectomies, are fraught with vision threatening complications and can induce chronic irritation or bleb dysaesthesia.

In my previous blog, I discussed my rationale for coupling micro-invasive glaucoma surgeries or MIGS with cataract surgery in eyes controlled with medications.  My objective for performing MIGS was to reduce or remove the daily application of caustic chemicals (a.k.a. glaucoma medications and associated preservatives) to help minimize the agony that patients experience.  Yes, I’m being a little melodramatic, but drops are not fun to use and they certainly cause pathologic changes to the eye and ocular adnexa, including the trabecular meshwork.  But, what about those patients with uncontrolled glaucoma with visually significant cataracts?  Can we take the same approach to manage their glaucoma and use a MIGS procedure?  I believe the answer is a resounding yes!  When I am managing my uncontrolled glaucoma patients, especially those with mild to moderate disease, I do not want to make the control worse than the condition.  I realize our goal is to preserve vision, but I want to take a patient’s quality of life into consideration.  I do not want to automatically subject them to a disfiguring, somewhat medieval procedure that can over-filter, induce astigmatism and just simply cause the patient to be perpetually aware that their eyes exists.  Not to mention the potential need for needling revisions and/or multiple anti-metabolite injections, which we know can cause severe ocular surface disease.

If a patient has uncontrolled mild to moderate glaucoma and a visually significant cataract I couple their cataract extraction with one (or two) of my many tools in my MIGS toolbox.  Like my controlled patients, I usually choose a procedure that maximizes outflow through the conventional outflow system, as it lends itself to be a safer approach to lower IOP than the suprachoroidal or subconjunctival spaces.  But that is not to say I avoid these two spaces, because I use them quite often.  I’ve found that trabecular iStent micro-bypass (Glaukos, San Clemente, CA) or viscodilating the canal using the iTrack illuminated microatheter (Ellex, Adelaide,  Australia) can effectively reduce a patient’s IOP to target levels, while at the same time reduce their need for topical medications.1,2 “  In fact, I have had a drastic reduction in my need to perform filtration procedures because of MIGS.  With the plethora of devices and procedures available, it is important to understand aqueous outflow anatomy and the inherent pathologic changes that occur within the system with age and in glaucoma.  This understanding will allow one to choose a procedure that best fits the individual patient and maximize outcome.

The key to my decision-making is my pre-operative evaluation of the angle (Please perform gonioscopy prior to scheduling a patient for a MIGS procedure.  Some of you are not and you know who you are!!!).  I want to see the prototypical banding of the angle and a nice homogenous band of pigmentation of the of the posterior trabecular meshwork.  In an angle with this hallmark anatomy, I presume that the migration of aqueous is through a relatively intact proximal and distal outflow system and that the system is amenable to augmentation with a MIGS procedure.  Of course, aqueous outflow is segmental and there are various barriers or areas of increased resistance to aqueous filtration, which ultimately serves as a foundation for my approach to each individual patient.

Should I see an angle devoid of the unadulterated segments of the TM or if the angle appears atrophic or has significant areas with goniosynechiae I will either opt to utilize the suprachoroidal/supraciliary space or even choose one of the trabecular ablative procedures.  The reader may ask: “Why not just start with the supraciliary/suprachoroidal space or perform an ablative procedure for all patients with mild to moderate glaucoma undergoing cataract extraction?”  Some may choose these as their first-line MIGS for all patients, but I am a bit more reserved with my tree of therapy.  Firstly, I prefer to minimize my MIGS footprint on the eye so that I may manipulate the system in the future if needed.  We all know we don’t have that magic procedure that works 100% of the time in 100% of patients for infinity.  With procedures like ABiC or iStent implantation, I know I can always come back and tweak the outflow system with any other glaucoma procedure.  I can still do 360 degrees of SLT. I can perform ABiC after an iStent or an iStent after ABiC.  Also, we may have some new tools in the near future that have stand-alone indications like the Hydrus Microstent (Ivantis, City, State) or the iStent SA (Glaukos, San Clemente, CA).  If I start with a procedure that removes the TM in an exaggerated (will expand in future blog) fashion, I will have forever crippled my hands in managing that eye in a micro-invasive fashion.

Second, I like keeping my aqueous pump intact.  (If you have not read Murray Johnstone’s work, please stop reading this blog, but just for a second, go to PubMed and read away).  I opine that the aqueous pump is required to maintain patency of the collector channels and distal system.  The trabecular meshwork is also the site of our newest drugs to treat glaucoma in latanoprostene bunod and netarsudil.  These medications act by relaxing actin/myosin complexes within the trabecular lamellae and increase the spaces between the trabecular columns and within Juxtacanalicular space.  Removal of the TM may hinder the action of these medications and may disallow the patients from being successful responders to our newest medications.  And thirdly, the inner wall of Schlemm’s canal is a blood-aqueous barrier and its removal can subject patients to recurrent hyphema development.3  BUT, trabecular ablative procedures are certainly needed and serve a critical role in many patients.  Likewise, using the supraciliary space as a corridor for aqueous displacement is also very important, so don’t get on eBay and sell your devices just yet.  In my next blog, I will discuss when and where I use trabecular ablative procedures and the supraciliary/suprachoroidal space to maximize patient outcomes.  Until then…


  1. Gallardo MJ, SupnetRA, Giamporcaro JE, Hornbeak DM. Outcomes of combined trabecular micro-bypass and phacoemulsification in a predominantly Hispanic patient population. Clin Ophthalmol. 2016 Oct 11;10:1931-1937. eCollection 2016. Erratum in: Clin Ophthalmol. 2016 Dec 09;10 :2475.

  2. Gallardo, MJ, Efficacy of Standalone and Combined Phacoemulsification-Ab Interno Canaloplasty in Patients with Primary Open-Angle Glaucoma”, ASCRS 2018, Washington (SPS-104 MIGS/Laser/Other Surgery)

  3. Ahuya Y, Malihi M and Sit A. Delayed-onset symptomatic hyphema after ab interno Trabeculotomy surgery. Am J Ophthalmology 2012;154:476-480.
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