The suprachoroidal space may be a better target for glaucoma surgery than the subconjunctival space, reducing wound-related complications while still effectively diverting aqueous. Preliminary reports from clinical trials of suprachoroidal shunt devices suggest that this approach is safe and effective.
"Blebless surgery is going to appeal to anyone taking care of glaucoma patients. We need a different target for the aqueous, and the suprachoroidal space is one such target," said Dr. Fechtner said, a professor of ophthalmology and director, glaucoma division, Institute of Ophthalmology and Visual Science, UMDNJ–New Jersey Medical School, Newark.
The subconjunctival space has been a very appealing target for glaucoma surgery because it is extraocular, easily accessible, the hydrostatic pressure approaches zero, and it has a virtually unlimited capacity for aqueous, Dr. Fechtner said. "However, it turns out that the subconjunctival space is a woefully unpredictable target for aqueous diversion," he added. "We know that trabeculectomy is the worst glaucoma operation that we have, except for all the other options previously available."
In the quest for blebless surgery, the suprachoroidal space is an attractive alternative target, he said. "There is physiologic flow to the suprachoroidal space. When there is excessive fluid there, there is choroidal detachment, so our balance is, can we divert the aqueous flow to that space without complications?"
The hydrostatic pressure in the suprachoroidal space is lower than the IOP, as measured in cynomolgus monkeys, Dr. Fechtner said, and this pressure differential could be used medically or surgically to alter the IOP.
Shunt devices have been introduced to divert aqueous to the suprachoroidal space, Dr. Fechtner said, and data are emerging from the first trials.
"The strategy of the suprachoroidal shunt is to access the suprachoroidal space from the anterior chamber and, preferably, leave the scleral spur intact," he said.
Shunt being studied
One of the newer suprachoroidal shunt devices (Gold Micro-Shunt, SOLX) received CE mark approval in 2005 and is undergoing clinical trials in the United States. Made of 24-karat gold, the device is 5.2 mm long, 3.2 mm wide, and 60 μm thick. It is designed with multiple channels to allow aqueous to flow through the shunt.
The shunt is implanted using a scleral approach with the tip in the anterior chamber and the tail in the suprachoroidal space.
Preliminary results are available from a nonrandomized, not-yet-published study of 76 eyes with a mean preoperative IOP of 27.5 mm Hg. The results available so far showed that a 37% reduction in IOP to 17.4 mm Hg reported at 3 months was being maintained out to 12 months and in some cases 24 months, Dr. Fechtner said.
"Serious complications are our initial concern," he continued. Reported in the first 76 eyes and an additional 14 reported on later, such complications included one shunt extrusion and one retinal detachment. Other reported complications were transient hypotony and transient hyphema. No suprachoroidal hemorrhages were reported in that series. It remains to be seen if complications are more common in prospective clinical trials, Dr. Fechtner said.