Comparing Viscocanalostomy with Trabeculectomy

Abstract

In recent years, non-penetrating glaucoma surgery has been seen as a safer alternative to trabeculectomy. This class of procedures is mainly represented by 'deep sclerectomy', 'viscocanalostomy,' and 'canaloplasty' (a recent and more reproducible variation of viscocanalostomy). The aim of all these procedures is to allow drainage of the aqueous humor from the anterior chamber, not through a patent scleral opening but by slow percolation through the inner trabecular meshwork and/or Descemet's membrane ('sclerodescemetic membrane'). This avoids sudden drops in intraocular pressure (IOP), hypotony, and flat chambers. The absence of anterior chamber opening and iridectomy limits the risk of cataract and infection. The advantages of viscocanalostomy and canaloplasty are that not only are they non-penetrating, like deep sclerectomy, but also, most importantly, they restore the physiologic outflow pathway, thus avoiding external filtration in the majority of eyes. This makes the success of the procedure partly independent of conjunctival or episcleral scarring, a leading cause of failure in trabeculectomy, with fewer indications for wound healing modulation. Moreover, the absence of an elevated filtering bleb avoids related ocular discomfort, and the procedures can be carried out in any quadrant. Operative TechniqueViscocanalostomy is a demanding surgical technique that requires a long learning curve. As soon as the window is completed, the inner scleral flap is excised.The next step is the sealing of the lake, which is obtained by tightly suturing the outer scleral flap with seven 10-0 nylon stitches.High-molecular-weight sodium hyaluronate is then injected underneath the flap to fill the intrascleral space temporarily, preventing it from collapsing and scarring in the early post-operative period. Finally, the conjunctiva is sutured in place. Mechanism of ActionViscocanalostomy increases the aqueous outflow through different paths. Injection of viscoelastic into the canal not only dilates the canal and associated collectors but also disrupts the internal and external walls of Schlemm's canal and adjacent trabecular layers, thus increasing the trabecular outflow facility and making the procedure act as a 'micro-trabeculotomy' (see Figure 5).

Combined Approach to Coexisting Glaucoma and Cataract: Choice of Surgical Techniques

“…Viscocanalostomy, a relatively new, non-penetrating filtering surgical procedure has been reported to efficiently and safely reduce intraocular pressure (IOP) in various types of open-angle glaucoma (OAG). (Carassa et al, 2002).When combined with phacoemulsification surgery, viscocanalostomy (phacoviscocanalostomy) has similarly been reported to efficiently and safely reduce IOP while improving visual acuity. For a combined phacoviscocanalostomy the following procedure is followed.…”

“…If we also take into consideration the cost effectiveness of combined versus two-stage procedures, phacoviscocanalostomy appears to be a rational therapeutic approach for the treatment of uncontrolled OAG with concomitant age-related cataract. (Carassa et al, 2002). Furthermore, taking into account the potentially serious complications of phacotrabeculectomy, the need for safer and still effective alternative surgical procedures is mandatory.…”