Surgical procedures for glaucoma aim to reduce intraocular pressure (IOP) resulting from impaired aqueous humor drainage in the trabecular meshwork and/or Schlemm’s canal. In the primary (conventional) outflow pathway from the eye, aqueous humor passes through the trabecular meshwork, enters a space lined with endothelial cells (Schlemm’s canal) and then drains into the aqueous veins. Increases in resistance in the trabecular meshwork and/or the inner wall of Schlemm’s canal can disrupt the balance of aqueous humor inflow and outflow, resulting in an increase in IOP and glaucoma risk.
Surgical intervention may be indicated in patients with glaucoma when the target IOP can not be reached pharmacologically. Trabeculectomy (guarded filtration surgery) is the most established surgical procedure for glaucoma, allowing aqueous humor to directly enter the subconjunctival space. This procedure creates a subconjunctival reservoir which can effectively reduce IOP, but commonly results in filtering “blebs” on the eye, and is associated with numerous complications (e.g., leaks or bleb-related endophthalmitis) and long-term failure. The Trabectome™ is a recently developed electrocautery device with irrigation and aspiration designed to selectively remove trabecular meshwork and Schlemm’s canal inner wall.
Canaloplasty involves dilation and tension of Schlemm’s canal with a suture loop between the inner wall of the canal and the trabecular meshwork. Canaloplasty utilizes the iTrack™ illuminated microcatheter (iScience Interventional) to access and dilate the entire length of Schlemm’s canal and to pass the suture loop through the canal. Other surgical procedures (not addressed in this policy) include trabecular laser ablation, deep sclerectomy, which removes the outer wall of Schlemm’s canal and excises deep sclera and peripheral cornea, and viscocanalostomy, which unroofs and dilates Schlemm’s canal without penetrating the trabecular meshwork or anterior chamber.
A variety of trabecular shunts are being developed as minimally penetrating methods to drain aqueous humor from the anterior chamber into an ocular reservoir. These include the iStent (Glaukos), which is inserted into the end of Schlemm’s canal by an internal (through the cornea and anterior chamber) or external approach (through the subconjunctiva); the EyePass Bi-Directional Glaucoma Implant (GMP Companies), which is a Y-shaped shunt in which the 2 arms are placed into both lumina of Schlemm’s canal ab externo; and the Solx DeepLight Gold Micro-Shunt (OccuLogix), which shunts aqueous humor between the anterior chamber and the suprachoroidal space. Since aqueous humor outflow is pressure dependent, the pressure in the reservoir and venous system are critical for reaching the target IOP. Therefore, some devices may be unable to reduce IOP below the pressure of the distal outflow system used, e.g., below 15 mm Hg. Each type of shunt and approach to insertion may produce different results and are thus viewed as distinct interventions.
The iTrack (iScience Interventional) received 510(k) marketing clearance from the U.S. Food and Drug Administration (FDA) in 2004 as a surgical ophthalmic microcannula which is indicated for the general purpose of “fluid infusion and aspiration, as well as illumination, during surgery.” The iStent and Eyepass are currently in FDA trials (the iStent trial’s FDA investigational device exemption [IDE] designates the iStent as a category B device). The Micro-Shunt has received regulatory approval in Europe. These are not FDA approved for use in the U.S. at this time.
Note: Not discussed in this policy are the AquaFlow™ Collagen Glaucoma Drainage Device, which received FDA premarket approval in 2001 for the maintenance of sub-scleral space following non-penetrating deep sclerectomy, and the Ex-PRESS™ Mini Glaucoma Shunt, which received 510(k) marketing clearance in 2003 to transport aqueous fluid from the anterior chamber of the eye into a conjunctival bleb.

Insertion of an anterior segment aqueous drainage device (e.g., trabecular shunt) without an extraocular reservoir is considered investigational as a method to reduce intraocular pressure in patients with glaucoma.
Canaloplasty is considered investigational as a method to reduce intraocular pressure in patients with glaucoma.

There will be a new CPT category III code for this procedure effective July 2008:

0191T: Insertion of anterior segment aqueous drainage device, without extraocular reservoir; internal approach

0192T – Insertion of anterior segment aqueous drainage device, without extraocular reservoir; external approach
These procedures might have previously been coded using one of the following codes:
66180: Aqueous shunt to extraocular reservoir
66170: Fistulization of sclera for glaucoma; trabeculectomy ab externo in absence of previous surgery
66172: Fistulization of sclera for glaucoma; trabeculectomy ab externo with scarring from previous ocular surgery or trauma (includes injection of antifibrotic agents)
66999: Unlisted procedure, anterior segment of eye.
The new category III CPT codes specify shunting without drainage to an extraocular reservoir.
The insertion of the iTrack device for subchoroidal delivery of pharmacologic agents is coded using 0186T and is addressed in MPRM policy 9.03.19. There is no specific CPT coding for insertion of the iTrack device for illumination during surgery.
Canaloplasty would be coded using the following code:
0177T: Transluminal dilation of aqueous outflow canal; with retention of device or stent

BlueCard/National Account Issues

State or federal mandates (e.g., FEP) may dictate that all FDA-approved devices, drugs or biologics may not be considered investigational and thus these devices may be assessed only on the basis of their medical necessity.

1. Spiegel D, Wetzel W, Haffner DS et al. Initial clinical experience with the trabecular micro-bypass stent in patients with glaucoma. Adv Ther 2007; 24(1):161-70.
2. Dietlein TS, Jordan JF, Schild A et al. Combined cataract-glaucoma surgery using the intracanalicular Eyepass glaucoma implant: first clinical results of a prospective pilot study. J Cataract Refract Surg 2008; 34(2):247-52.
3. http://www.clinicaltrials.gov/ct2/results?term=glaucoma+AND+shunt Last viewed June 2008.
4. Lewis RA, von Wolff K, Tetz M et al. Canaloplasty: circumferential viscodilation and tensioning of Schlemm's canal using a flexible microcatheter for the treatment of open-angle glaucoma in adults: interim clinical study analysis. J Cataract Refract Surg 2007; 33(7):1217-26.

Canaloplasty

Eyepass

iStent

iTrack

Trabectome

Trabecular Shunt