|Ab interno glaucoma devices|
|Monday, 04 March 2013|
Francis BA, Winarko J. Ab interno Schlemm’s canal surgery: trabectome and iStent. DevOphthalmol. 2012; 50:125-36.
In a nutshell
The second electrode at this point lies on the surface of the trabecular meshwork, which is destroyed as the cautery is activated. The canal electrode is advanced within the canal, and the meshwork is destroyed as far as the instrument can be advanced, in an arc of about 30°. It is then reversed so that another 30° of meshwork can be destroyed, leaving a 60° sector of canal of Schlemm exposed to the anterior chamber, thus improving aqueous drainage.
The second, known as the iStent, is a tiny, precisely shaped tube that can be inserted from the anterior chamber, under gonioscopic control, into the canal of Schlemm, thus allowing aqueous to bypass the trabecular meshwork. This can be done during cataract surgery, or as a single procedure.
Sight-threatening complications of this surgery can arise from excessive aqueous drainage. The two devices described here create only a partial drainage path, from the anterior chamber to the canal of Schlemm. The trabectome was introduced in 2006 and evidence gathered since then seems to indicate that it is effective. The iStent is a more recent invention and, although it has been passed by the FDA, it has yet to stand the test of time.
Both devices bypass the trabecular meshwork, thought to be the main area of obstruction in glaucoma, and both avoid the problem of excessive conjunctival scarring and healing, the commonest cause of trabeculectomy surgical failure.