39 Combining Minimally Invasive Glaucoma Surgery Procedures

A 65–year-old man with a history of pseudoexfoliation syndrome presented with gradual vision loss in his right eye. Initial examination demonstrated classic pseudoexfoliative (PXE) material on the anterior capsule and pupillary margin (Fig. 39.1). His right eye had moderate cataract with phacodonesis, pigment peppering on the iris stoma, and iris transillumination defects more prominent inferiorly. Gonioscopy showed appositional angle closure in his right eye and a double hump configuration of the iris noted bilaterally, with 2–3+ trabecular meshwork pigmentation. Fundus examination showed excavation of both optic nerves with an inferior notch in the right eye. Although the patient was initially treated with glaucoma medication, his intraocular pressure (IOP) remained above target and his visual fields were progressing.

The diagnosis was pseudoexfoliation glaucoma with phacodonesis from zonular dehiscence, as well as appositional angle closure from a combination of plateau iris and an anteriorly shifted lens. A combined ICE (iStent, cataract extraction, and endocyclophotocoagulation) and MIGS (minimally invasive glaucoma surgery) procedure was planned (Fig. 39.2). A femtosecond laser–assisted cataract extraction with a capsular tension ring was performed, with a central deepening of the anterior chamber noted after lens extraction. With the intraocular lens (IOL) in place, two trabecular bypass stents were inserted in the nasal quadrant next to pigmented areas of trabecular meshwork and adjacent collector channels. Finally, endocycloplasty was performed to further open up the angles and reduce aqueous humor production.

This case demonstrates the utility of combining MIGS procedures to properly target the multiple mechanisms causing glaucoma and minimizing the risks of penetrating surgery (Table 39.1).

The Procedures

Traditionally, glaucoma surgeons have relied on a handful of procedures, the most notable being trabeculectomy, a filtering procedure that reroutes aqueous humor from the anterior chamber to the sub-Tenon’s and subconjunctival space. Another widely used procedure is the implantation of valved or nonvalved glaucoma drainage devices such as the Ahmed or Baerveldt implants. Although these surgeries may be effective in lowering the IOP, significant postoperative risks exist and aggressive healing may impede surgical success.¹

Recently, a new paradigm in glaucoma management was introduced and coined as MIGS.² These newer techniques are changing glaucoma surgery in a similar fashion to the way that small incision phacoemulsification changed cataract surgery, in that MIGS procedures by nature are less invasive and use microincisions. The newer materials, smaller devices, and microinstrumentation have changed the traditional ab externo approach to an ab interno one, thus sparing the conjunctival tissue for future surgeries.

Commonly used MIGS procedures target the trabecular outflow pathway, the most common of which is the iStent Trabecular Micro-Bypass (Glaukos Corp., Laguna Hills, CA). However, newer procedures are being developed and utilize other glaucoma outflow pathways. Table 39.1 categorizes the current MIGS procedures.

Categorizing MIGS procedures by their main mechanism of IOP reduction enables surgeons to more effectively combine them and target the different underlying mechanisms of the patient’s disease.

Aqueous Humor Reduction

Historically, medications and transscleral cyclophotocoagulation were used to decrease aqueous humor production to treat glaucoma. However, with the development of endocyclophotocoagulation (ECP), surgeons can now utilize this minimally invasive technique to create focalized treatment of the ciliary body. In contrast to other MIGS procedures, ECP decreases aqueous humor production. This approach can easily be employed in combination with other MIGS procedures that act on different glaucoma pathways and ultimately reduce the IOP to the desired level.

Usually, ECP can be used in all cases of open- or closed-angle glaucoma. However, one may wish to avoid it in uveitic patients or patients prone to ciliary body shutdown.

Narrow Angle

Plateau iris syndrome is characterized by anteriorly rotated or large ciliary processes that displace the iris and close the angle. Clinically, this syndrome does not resolve with peripheral laser iridotomy. Ophthalmologists have developed the endocycloplasty procedure to shrink the ciliary processes. Combined with cataract extraction, this procedure helps to open the angle.

Cataract extraction can be regarded as one of the first MIGS procedures. It has been hypothesized that phacoemulsification reduces IOP by increasing aqueous outflow facility.^3,4 However its effect is more important on angle-closure glaucoma.⁵ Thus, one may advocate utilizing lens extraction as a MIGS procedure in acute and chronic angle closure, phacomorphic glaucoma, plateau iris syndrome, pseudoexfoliative glaucoma, or any cause of phacodonesis resulting in an anteriorly displaced lens.

Lastly, goniosynechialysis can also be considered as a MIGS procedure, especially for patients who previously had an acute episode of angle-closure glaucoma and have recent peripheral anterior synechiae (PAS).⁶

Fig. 39.1 Pseudoexfoliation syndrome. Classic pseudoexfoliative (PXE) material is visualized on the anterior capsule and pupillary margin. One can notice pigment peppering on the pupillary border, most notably on the inferior portion of the iris.

Fig. 39.2 Combined ICE (iStent, cataract extraction, and endocyclophotocoagulation) and MIGS (minimally invasive glaucoma surgery) procedure. Preoperative visualization of the ciliary body and nasal angle with two properly place iStents after cataract extraction and intraocular lens implantation using the endocyclophotocoagulation probe.

In contrast to other procedures, MIGS procedures targeting the trabecular meshwork have the advantage of utilizing the natural conventional outflow pathway. Existing procedures in this category are trabecular bypass stenting with the iStent and trabeculotomy ab interno with the Trabectome (NeoMedix, Tustin, CA). Other procedures and devices that utilize this mechanism of action are currently in development.7 These trabecular bypass devices can be used for all primary or secondary open-angle glaucomas. One may also advocate their use in patients with mixed-mechanism glaucoma whose angles have opened after lens extraction. However, their use in patients suspected of having elevated episcleral venous pressures or diseased distal outflow pathways pathologies (nonfunctional collector drainage system) should be avoided.

Suprachoroidal Shunts

Prostaglandin analogue drops have extensively been used to exploit the uveoscleral outflow pathway. Although it is not the main mechanism by which aqueous humor drains, it constitutes a second natural pathway for IOP reduction. Thus, newer MIGS devices such as the CyPass Micro-Stent (Transcend Medical Inc., Menlo Park, CA) and the iStent Supra are being developed to utilize the suprachoroidal space. This potential space has a negative pressure compared with the anterior chamber, thus creating a gradient for aqueous humor to egress.⁸

This alternative surgical option can be useful in patients with poorly functioning trabecular outflow pathways, scarred subconjunctival tissue, or poor integrity of conjunctiva tissue, and in patients at high risk for scarring. Similarly to trabecular bypass devices, patients with suspected elevated episcleral venous pressures are also poor candidates for this category of MIGS procedures.

Transconjunctival Filtration

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