I am often asked, “How long does canaloplasty last?” The answer I most often give (and the one that applies to all glaucoma surgeries) is, “I don’t know.” Over time most glaucoma surgeries fail to maintain an adequately low intraocular pressure (IOP). Comparing failure rates among glaucoma surgeries, however, can be challenging. Why? Because not all studies share the same definition of “failure.”
Failure Rates for Trabeculectomy and Glaucoma Drainage Devices
One of the definitions of failure used in the Tube versus Trabeculectomy study was an IOP greater than 17mmHg or and IOP reduction of less than 20% on two consecutive measurements. Using these failure criteria trabeculectomies fail at a rate of approximately 10% per year whereas glaucoma drainage devices fail at a rate of just over 5% per year.[1]
But many patients who undergo trabeculectomy or tube placement require an IOP reduction into the low teens. If “failure” is redefined to reflect this goal then trabeculectomies fail at a rate of approximately 15% per year whereas glaucoma drainage devices fail at a rate of approximately 10% per year.[2]
Failure Rates for Canaloplasty and Phacocanaloplasty
The 3-year US study defined failure as an IOP greater than 18mmHg (with or without drops) over two consecutive visits. This is a reasonable target IOP considering that most patients who are offered canaloplasty have early to moderate glaucoma.
Canaloplasty failure rates appear to be dependent upon whether cataract surgery (phacoemulsification) was done at the time of canaloplasty (this is called phacocanaloplasty). Of those who had canaloplasty alone, the rate of failure was similar to that of trabeculectomy or glaucoma drainage devices. However, of those who had cataract surgery plus canaloplasty (phacocanaloplasty) the rate of failure was less than 10% even three years out from surgery![3] That’s a failure rate of only 3% per year.
Failure Rates for Viscocanalostomy
Canaloplasty is an improvement upon an older non-penetrating surgery called viscocanalostomy. Conceived of by Dr. Robert Stegmann over two decades ago, there is now data to suggest that this surgical procedure can last for over a decade. According to a recently published study,[4] average IOP was amazingly stable over the first ten years after surgery: 15.4 ± 3.6 mmHg at 5 years and 15.5 ± 4.4 mmHg at 10 years. By 15 years out from surgery there was a mild increase in IOP (16.8 ± 4.2 mmHg) though this was still quite an improvement from the average pre-surgery IOP of 42.6 ± 14.2 mmHg.
If viscocanalostomy can achieve such impressive long-term results then it’s quite reasonable to believe that canaloplasty (essentially “viscocanaloplasty-plus) would result in even greater long-term IOP reduction. Early comparisons of these glaucoma surgical procedures support such a belief. A published comparison of canaloplasty against viscocanaloplasty noted that 18 months after surgery the IOP averaged almost 2mmHg lower in the eyes that had undergone canaloplasty compared to those eyes that had undergone viscocanalostomy.[5]
“Will this glaucoma surgery work for me and if so for how long?”
That’s the question those facing glaucoma surgery are really asking. Unfortunately, no one has the answer to that question. The best we can do is provide an estimate based on the available literature. For those with mild to moderate glaucoma with target IOPs in the mid- to upper-teens canaloplasty can be expected, on average, to achieve and maintain IOP lowering for years.
References:
1) Gedde SJ, Schiffman JC, Feuer WJ, et. al. Treatment Outcomes in the Tube Versus Trabeculectomy (TVT) Study After Five Years of Follow-up. Am J Ophthalmol. 2012 [Article in Press].
2) Gedde SJ, Schiffman JC, Feuer WJ, et. al. Treatment Outcomes in the Tube Versus Trabeculectomy (TVT) Study After Five Years of Follow-up. Am J Ophthalmol. 2012 [Article in Press].
3) Lewis RA, von Wolff K, Tetz M, et al. Canaloplasty: three-year results of circumferential viscodilation and tensioning of Schlemm canal using a microcatheter to treat open-angle glaucoma. J Cat Ref Surg. 2011;37(4):682-690.
4) Grieshaber MC, Peckar C, Pienaar A, et. Al. Long-term results of up to 12 years of over 700 cases of viscocanalostomy for open-angle glaucoma. Acta Ophthalmol. 2014 [Article in PressDOI: 10.1111/aos.12513]
5) Koerber NJ. Canaloplasty in one eye compared with viscocanalostomy in the contralateral eye in patients with bilateral open-angle glaucoma. J Glaucoma. 2012;21(2):129-34.
