Surgery Section - Emerging Surgical Treatments for Glaucoma

IMPORTANT REMINDER

This Medical Policy has been developed through consideration of medical necessity, generally accepted standards of medical practice, and review of medical literature and government approval status.

Benefit determinations should be based in all cases on the applicable contract language. To the extent there are any conflicts between these guidelines and the contract language, the contract language will control.

The purpose of medical policy is to provide a guide to coverage. Medical Policy is not intended to dictate to providers how to practice medicine. Providers are expected to exercise their medical judgment in providing the most appropriate care.

Description

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.

Policy/Criteria

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.

Scientific Background

A search of the MEDLINE database was performed through June 2008 and found minimal data regarding the use of either trabecular shunts or canaloplasty for the treatment of glaucoma.

Trabecular Shunts

To date, the published literature on aqueous drainage devices consists of small case series. (2-4) A number of clinical trials are in progress, and the iStent is being studied under a FDA category B investigational device exemption. (5) None of these devices has been approved by the FDA. Therefore, insertion of drainage devices for glaucoma is considered investigational.

Canaloplasty

References

1. BlueCross BlueShield Association Medical Policy Reference Manual, Policy No. 9.03.21
2. 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
3. Spiegel D, Kobuch K. Trabecular meshwork bypass tube shunt: initial case series. Br J Ophthalmol. 2002;86(11):1228-31
4. 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
5. http://www.clinicaltrials.gov/ct2/results?term=glaucoma+AND+shunt (Verified 8/25/08)
6. 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

Cross References

None

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