Modern Glaucoma Surgery

Modern Glaucoma Surgery

some surgeons inject viscoelastic into both openings of Schlemm’s canal to stretch it and potentially open

more widely the outflow channels that carry aqueous out of Schlemm’s canal. Aqueous can now

percolate through Descemet’s membrane into the scleral pocket, where it can then flow into Schlemm’s

canal and exit the eye through the normal drainage channels. Some surgeons also place a collagen

implant into the scleral pocket—this implant dissolves over time but prevents the pocket from scarring

down in the early postoperative period when healing is maximized. The outer scleral flap is sewn down

tightly because fluid is not meant to ooze from under the flap into a bleb. The procedure is difficult to

perform and has been largely abandoned.

Canaloplasty

Canaloplasty differs from all the other procedures in that there is technically no new outflow pathway

created. A scleral flap is created, and the outer wall of Schlemm’s canal is opened under the flap. A long,

thin probe is passed into one end of Schlemm’s canal and advanced around the entire length of the canal

to emerge from the opposite end. A suture is then attached to the end of the probe, which is withdrawn,

leaving the suture in Schlemm’s canal. The suture is tied with just enough tension to tug Schlemm’s canal

and the trabecular meshwork inward on themselves. The mechanism by which this lowers IOP is

unknown, although it may alter the anatomy of the trabecular and/or uveoscleral outflow pathways in a

way that promotes aqueous flow from the eye. This procedure is difficult to perform and requires the

purchase of the specialized probe used to place the suture into the canal. It is infrequently performed by

only a few surgeons.

CILIOABLATION PROCEDURES

Aqueous fluid is produced by the ciliary processes of the ciliary body. When efforts to improve aqueous

outflow fail or are not indicated, IOP can still be lowered by surgical procedures designed to destroy the

ciliary processes and reduce aqueous inflow into the eye. Typically these are end-stage procedures

reserved for blind eyes that would otherwise require enucleation or in order to save the residual vision in

an eye that has failed all other feasible procedures.

The procedure can be performed using either heat in the form of a laser or cold in the form of a

cryoprobe. In both cases, the procedure is performed through the sclera just posterior to the limbus,

where the ciliary processes are located just inside the eye. The circumference of the eye is treated in

multiple spots. The three o’clock and nine o’clock spots are left untreated as corneal nerves pass through

these spots and should be spared to avoid leaving the cornea without nerves, which will lead to corneal

decompensation over time. Many surgeons also leave one quadrant fully untreated to avoid hypotony.

Hypotony is a real concern in this procedure, and it is essentially irreversible as the damage cannot be

undone and can lead to phthisis. Hyphema and inflammation are also common and may linger for a long

time postoperatively given that there is little outflow to carry the blood and inflammatory cells out of the

eye. Both steroids and cycloplegic agents are typically prescribed in the postoperative period. The

procedure is also very painful, so that a retrobulbar anesthetic block is required preoperatively and

patients usually require narcotic medications for pain control in the early postoperative period.

One exception to these general rules is endocyclophotocoagulation (ECP). ECP is a gentler form of

cilioablation that can be performed on eyes with good vision in order to reduce IOP and/or reduce the

medication burden. The procedure is often combined with cataract surgery and is performed using a

small endoscopic probe that is inserted into the eye through a small incision in the peripheral cornea. The

probe has a camera to guide the treatment and a laser to deliver the treatment. Individual ciliary

processes can be targeted, which allows more control over the extent of treatment than the above

procedures that are done through the sclera with no direct visualization of the extent of treatment

performed. For this reason, the procedure is more predictable and overtreatment leading to hypotony is

extremely rare. But because there is still some risk of chronic, irreversible hypotony, this procedure is only

performed by a handful of surgeons who feel comfortable taking that small risk in otherwise healthy eyes

with good visual potential and early-to-moderate glaucoma.