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Page 2 of 7 Wiens et al. Mini-invasive Surg 2021;5:8 I http://dx.doi.org/10.20517/2574-1225.2020.105

INTRODUCTION
Glaucoma stands as the leading cause of irreversible blindness worldwide and approximately 3% of the
[1]
population between 40-80 years old have a primary open angle glaucoma . While a trabeculectomy is
considered as the gold standard treatment for glaucoma management, the use of micro-invasive glaucoma
surgeries (MIGS) for the treatment of mild to moderate glaucoma are growing due to their high safety
[2,3]
profile, rapid recovery time, and minimally invasive nature . Canal-based MIGS procedures attempt
to bypass the trabecular meshwork, a major site of resistance to aqueous humor drainage, and enhance
[4]
the conventional outflow . While the true efficacy of MIGS procedures is still to be elucidated, surgeons
are discovering that device design and surgical expertise are not the sole determinants of treatment
success. The placement of these devices in terms of optimal orientation to best enhance aqueous outflow
is of paramount importance, giving rise to the term “targeted MIGS”. Implantation of iStents (Glaukos
Corporation, Laguna Hills, CA, USA) is one such canal-based procedure. However, current literature
supports implantation of one to three iStents in areas of dense trabecular pigmentation, adjacent to major
aqueous and episcleral veins that are identified via external examination and/or in areas of focal blood
reflux in the Schlemm canal as seen with gonioscopy, in an attempt to target the major collector channel
[4]
ostia in anterior segments . The rationale is to target these large capacity veins to effectively enhance
aqueous drainage. We describe a reticular patterned episcleral venous plexus that comprises of a network of
numerous small-caliber, finer vessels, rather than a few, large-caliber vessels.

Gonioscopy assisted transluminal trabeculotomy (GATT) is a novel, ab interno MIGS approach to a
360-degree trabeculotomy that is conjunctival-sparing while also resulting in successful reductions in
[5]
intraocular pressure (IOP) and decreased need for glaucoma medications . A hemi-GATT unroofs
180-degrees of the Schlemm’s canal to reduce the risk of postoperative hyphema and reduces intraoperative
tissue manipulation. Both a 360 degree-GATT and hemi-GATT aim to improve aqueous outflow through
[5]
Schlemm’s canal and adjacent collector channels . Unlike in filtration surgery where bleb morphology
correlates with surgical success, to date there is no concrete evidence, whether pre-operative, intraoperative
or post-operative, of a similar association between bleb morphology and canal-based MIGS surgery .
[3]
However, growing evidence supports the correlation between the presence of an episcleral venous fluid
wave (EVFW) and post-operative reductions in IOP as well as the need for fewer glaucoma medications
[3]
and/or additional surgeries . An EVFW is an intraoperative technique performed at the conclusion of a
surgery wherein diffuse vessel blanching is achieved by injecting balanced salt solution (BSS) that flows
into the conjunctival and episcleral venous systems, demonstrating possible patency of the conventional
[3,6]
aqueous outflow system . For an EVFW to be present, fluid must be able to travel from collector channel
openings, through the deep and mid scleral plexuses to the episcleral plexus terminating in the conjunctival
[3]
veins, thereby demonstrating an enhanced aqueous outflow .

Due to the broad 180- to 360-degree area of treatment with hemi-GATT and GATT procedures
respectively, theoretically, one could propose that these procedures could be effective even in eyes
demonstrating a reticular patterned episcleral venous plexus as one could target large areas of Schlemm’s
canal rather than individual veins to enhance aqueous drainage. We propose that hemi-GATT is an
effective technique to enhance aqueous outflow in eyes that have a reticular patterned episcleral venous
plexus, with EVFW serving as an indicator of probable surgical success.

CASE REPORT
Description of the surgical technique
Using standard sterile eye preparation, the surgical eye was draped and held open with a wire lid speculum.
The inferior sector of the eye (inferior 180-degrees) was selected as the hemi-GATT target. The hemi-GATT
[5]
was performed using the ripcord technique, modified from that described by Grover et al. [Figure 1, Video 1].