**3. Types of migs techniques in the trabecular pathway**

All the surgical routes of the trabecular route seek the same aim (to facilitate the exit of aqueous humor from the anterior chamber to the systemic circulation) but they achieve it in different ways.


We can also differentiate the surgeries based on the area that they treat:


**27**

*3.1.4 Security*

*Cataract Surgery Combined with Trabecular MIGS (Minimally Invasive Glaucoma Surgery)*

It is an ab-interno MIGS technique in which two implants are applied in a specific way on the TM [5]. IStent is the smallest device ever implanted in humans [5]. It is a titanium implant surrounded by a layer of heparin, which allows better passage of the aqueous humor through the lumen of the iStent [5]. It has a long portion that enters the Schlemm's canal and a short portion that crosses the TM and connects with the anterior chamber [5]. The distal portion is beveled and tapered to facilitate penetration through the TM tissue and on the external surface it has three ridges that prevent its expulsion once inserted [5]. The Glaukos® GTS-400 trabecular implant has an applicator and a button to release the device and comes preloaded with two iStent, allowing the implantation of both iStent with a single applicator [5].

This implant is ideal for surgery combined with phacoemulsification, since the angle is easier to visualize in pseudophakic eyes [5]. Thus, IStent is indicated in combined use with cataract surgery for reduction of IOP in adult patients with mild–moderate open angle glaucoma (OAG) under treatment with topical hypoten-

It is contraindicated in patients with both primary and secondary angle closure glaucoma, including neovascular glaucoma, as well as in patients with retrobulbar tumors, thyroid orbitopathy, Sturge–Weber Syndrome or any other situation that

A gonioscopy should be performed prior to surgery to exclude peripheral anterior synechiae, rubeosis or any other abnormality of the chamber angle that may hinder a correct visualization of the angle that could produce a possible incorrect

For a safe surgery, it is essential to obtain a good visualization of the chamber angle by turning the patient's head 45° towards the opposite side of the operated eye and tilting the head of the surgical microscope 30° [5]. Intracamerular acetylcholine injection is first performed to constrict the pupil and the anterior chamber (AC) is filled with cohesive viscoelastic [5]. The main incision made for phacoemulsification is used to introduce the implant through the AC into the TM, while viewing the angle with gonioscopy and, once the insertion site is located, the tip of the implant (bevelled) is inserted into the TM, at an angle of about 15°, which facilitates penetration into the tissue, with the iStent tip pointing towards the patient's feet [4]. When it is verified that the TM covers the entire implant, it is released with the button of the applicator [5]. A small backflow of blood from the SC is frequent and reflects the proper position of the iStent [5]. Finally, the applicator is removed, the viscoelastic is washed and the corneal incision is sealed by hydrating the stroma [4].

Trabecular stent implantation is a safe procedure with limited complications and no severe adverse events [5]. The most common of complications is implant obstruction and malposition [5]. The appearance of minimal hyphema during

In **Figure 2(A)** we can see two iStent correctly implanted in the TM.

surgery is a sign of correct implant placement [5].

*DOI: http://dx.doi.org/10.5772/intechopen.95416*

*3.1.2 Indications and contraindications*

sive drugs and cataract in surgical stage [5].

placement of the iStent [5].

*3.1.3 Surgical technique*

may cause elevated episcleral venous pressure [5].

**3.1 iStent**

*3.1.1 Definition*

Some of these techniques are detailed below.

*Cataract Surgery Combined with Trabecular MIGS (Minimally Invasive Glaucoma Surgery) DOI: http://dx.doi.org/10.5772/intechopen.95416*

#### **3.1 iStent**

*Current Cataract Surgical Techniques*

In summary:

humor filtration.

the entire TM.

they achieve it in different ways.

with a laser (ELT).

are mainly found in the lower nasal area.

ocular pulse, eye movements).

circulation (it connects SC with the episcleral veins, that drain into the anterior and superior ciliary ophthalmic veins, which drain into the cavernous sinus) [3]. The organization of the collectors is not homogeneous, since they

• The trabecular pathway is a dynamic tissue that has a pumping system towards the systemic circulation and is influenced by IOP changes (especially blinking,

• In glaucoma there are some ultrastructural alterations that will produce a loss of elasticity of the trabecular pathway and therefore a decrease in aqueous

• These changes are more important in the juxtacanalicular portion of the TM.

• It is logical that the trabecular pathway is more or less affected depending on the type of glaucoma. A mild, incipient glaucoma, with a few years of evolution, will have less structural alterations than an advanced glaucoma, with

• In the same way, the different anatomical alterations will produce a greater or lesser alteration of the TM. For example, a glaucoma that does not present any alteration in gonioscopy is different than a pseudoexfoliative glaucoma, in which the pigment enters in the TM and the rest of the angular structures, or a pigment dispersion glaucoma, in which the pigment permeates very intensively

All the surgical routes of the trabecular route seek the same aim (to facilitate the exit of aqueous humor from the anterior chamber to the systemic circulation) but

a.Some techniques perform microperforations, either with an implant (iStent) or

c.Others perform a viscodilation of the SC, leading to the distension of the Schlemm canal, of the trabecular meshwork and of the collecting canals (ABiC, OMNI).

c.Others treat the entire circumference (360°) of the SC (OMNI, ABiC, GATT).

b.Others perform a rupture of the internal wall of the shlemm canal and the

We can also differentiate the surgeries based on the area that they treat:

b.Others treat a sector, normally 90° (ELT, trabectome, Kahook).

more years of evolution and that requires 2–3 drugs for its control.

**3. Types of migs techniques in the trabecular pathway**

trabecular meshwork (trabectome, Kahook, OMNI).

a.Some provide a punctual treatment (iStent).

Some of these techniques are detailed below.

**26**

#### *3.1.1 Definition*

It is an ab-interno MIGS technique in which two implants are applied in a specific way on the TM [5]. IStent is the smallest device ever implanted in humans [5]. It is a titanium implant surrounded by a layer of heparin, which allows better passage of the aqueous humor through the lumen of the iStent [5]. It has a long portion that enters the Schlemm's canal and a short portion that crosses the TM and connects with the anterior chamber [5]. The distal portion is beveled and tapered to facilitate penetration through the TM tissue and on the external surface it has three ridges that prevent its expulsion once inserted [5]. The Glaukos® GTS-400 trabecular implant has an applicator and a button to release the device and comes preloaded with two iStent, allowing the implantation of both iStent with a single applicator [5].

#### *3.1.2 Indications and contraindications*

This implant is ideal for surgery combined with phacoemulsification, since the angle is easier to visualize in pseudophakic eyes [5]. Thus, IStent is indicated in combined use with cataract surgery for reduction of IOP in adult patients with mild–moderate open angle glaucoma (OAG) under treatment with topical hypotensive drugs and cataract in surgical stage [5].

It is contraindicated in patients with both primary and secondary angle closure glaucoma, including neovascular glaucoma, as well as in patients with retrobulbar tumors, thyroid orbitopathy, Sturge–Weber Syndrome or any other situation that may cause elevated episcleral venous pressure [5].

A gonioscopy should be performed prior to surgery to exclude peripheral anterior synechiae, rubeosis or any other abnormality of the chamber angle that may hinder a correct visualization of the angle that could produce a possible incorrect placement of the iStent [5].

#### *3.1.3 Surgical technique*

For a safe surgery, it is essential to obtain a good visualization of the chamber angle by turning the patient's head 45° towards the opposite side of the operated eye and tilting the head of the surgical microscope 30° [5]. Intracamerular acetylcholine injection is first performed to constrict the pupil and the anterior chamber (AC) is filled with cohesive viscoelastic [5]. The main incision made for phacoemulsification is used to introduce the implant through the AC into the TM, while viewing the angle with gonioscopy and, once the insertion site is located, the tip of the implant (bevelled) is inserted into the TM, at an angle of about 15°, which facilitates penetration into the tissue, with the iStent tip pointing towards the patient's feet [4]. When it is verified that the TM covers the entire implant, it is released with the button of the applicator [5]. A small backflow of blood from the SC is frequent and reflects the proper position of the iStent [5]. Finally, the applicator is removed, the viscoelastic is washed and the corneal incision is sealed by hydrating the stroma [4]. In **Figure 2(A)** we can see two iStent correctly implanted in the TM.

#### *3.1.4 Security*

Trabecular stent implantation is a safe procedure with limited complications and no severe adverse events [5]. The most common of complications is implant obstruction and malposition [5]. The appearance of minimal hyphema during surgery is a sign of correct implant placement [5].

#### **Figure 2.**

*Surgical procedures. (A) Two iStent correctly implanted in the TM. (B) Kahook mades a cut along the TM in a clockwise direction, followed by another cut in an anti-clockwise direction. (C) During the application of the laser in ELT, the whitening of the TM and the appearance of one or more bubbles are observed. (D) OMNI introduces the blue microcatheter in the SC, first for 180º of the SC and then the process is repeated for the second 180º.*

## **3.2 ELT**

### *3.2.1 Definition*

ELT is an ab-interno MIGS technique in which microperforations or trabeculostomies are performed in the TM in order to facilitate the drainage of aqueous humor towards the SC using excimer laser impacts in a sectorial way (90°) of the TM [5]. Excimer laser photocoagulation allows the ablation of the juxtacanalicular wall of the TM and the internal wall of the Schlemm canal (avoiding injury to the external wall of the Schlemm canal containing fibroblasts, whose preservation is important for the drainage of the aqueous humor) with local and adjacent temperature control avoiding thermal damage to surrounding tissues [5].
