Choices in surgery
Choice of devices depends on extent of disease, presence of cataract
“I believe that the risk of glaucoma surgery should not exceed the disease risk,” said Thomas Samuelson, University of Minnesota, Minneapolis, USA, during his presentation at an ESCRS Main Symposium: Glaucoma for the Cataract Surgeon during the 36th Congress of the ESCRS in Vienna.
Dr Samuelson, a glaucoma specialist and the current president of the American Society of Cataract & Refractive Surgery, delineated his approach to glaucoma surgery. Besides keeping risk as low as possible, he prefers to “retain the outflow tract’s normal physiology when feasible”.
“The Level 1 evidence that cataract surgery lowers IOP in most patients with elevated IOP is undeniable, which is the foundational basis of combined surgery of phacoemulsification and MIGS,” said Dr Samuelson.
This evidence comes from the five prospective, randomised MIGS trials in which the control (phaco) arm significantly lowered IOP.
How best to manage coincident cataract and glaucoma? In cases in which cataract surgery alone is likely to deliver insufficient IOP-lowering, a complementary procedure is required.
“There are two broad classes of incisional glaucoma surgery. On the safer but maybe less efficacious end of the spectrum, we can perform surgery to augment physiological outflow,” he said.
This refers to canal surgery, and includes devices such as the iStent (Glaukos) and the Hydrus stent (Ivantis). Both are intracanalicular devices that are inserted into Schlemm’s canal to maintain patency and increase trabecular outflow.
Micro-incisional glaucoma surgery (MIGS) offers an alternative to high-outflow, low-resistance surgical options like supraciliary or transscleral methods that may ‘steal’ flow from physiological pathways and suffer surgical complications. In this sense, MIGS has forever changed the management of combined cataract and glaucoma, he noted.
“I find the canal to be very predictable. Remember, in mild-to-moderate disease, the trabecular meshwork is moderately dysfunctional, but not completely shot. Why abandon it?” he asked.
By using intracanalicular surgery, Dr Samuelson attempts to improve the physiological system before abandoning it.
“I treat mild-to-moderate phakic glaucoma, including combined surgery, differently than pseudophakic glaucoma. Once the eye is pseudophakic, I am far more willing to give up on the trabecular meshwork and Schlemm’s canal.”
However, when intracanalicular approaches will not provide sufficient IOP-lowering, a more aggressive approach is warranted. When greater efficacy is required, surgery can be performed to bypass physiological outflow, said Dr Samuelson, referring to supraciliary approaches, as with the CyPass
micro-stent, and transscleral approaches.
“Supraciliary stent implantation is very straightforward, with very good perioperative IOP and less steroid response,” he said.
This is his preferred approach when the canal is compromised or when one is willing to take more risk in light of disease severity.
“I approach the canal first, but I utilise the supraciliary option when needed,” he said.
Implantation of the CyPass creates a controlled cyclodialysis with stented outflow to the supraciliary space. However, Alcon announced on August 29, 2018, an immediate, voluntary market withdrawal of the CyPass micro-stent after researchers detected a concerning rise in endothelial cell loss compared with patients who underwent cataract surgery alone. This difference was not apparent at the two-year follow-up, but only became apparent at five years postoperatively.
Indeed, the addition of the MIGS procedure to cataract surgery must be safe. And it must be synergistic with phaco, which enhances physiological outflow through the trabecular meshwork.
“Iatrogenic vision loss keeps me awake at night,” he said.
And although MIGS can be very successful, Dr Samuelson reminded delegates to be willing to admit when it’s time to move on to a more aggressive approach.
How to decide between canal, transscleral or supraciliary?
“It’s not simply a matter of device label and disease severity. Severity is important, but it is only one factor. One must also consider compliance, medication tolerance and, most importantly, the likelihood and velocity of disease progression,” he advised.
Thomas Samuelson: firstname.lastname@example.org