New devices make strides in pediatric glaucoma

Take-Home

New devices for pediatric glaucoma surgery are becoming available that improve the ability to examine pediatric patients, perform surgeries more easily, and enhance treatment of difficult cases.

Dr. Freedman

By Lynda Charters; Reviewed by Sharon F. Freedman, MD

Durham, NC-Technologies for pediatric patients with glaucoma are helping to improve ophthalmologists’ ability to examine these young patients, perform selected surgeries, and treat difficult cases.

Still, such advances have been slow to progress over the years. There remains much room for the introduction of novel devices, according to Sharon F. Freedman, MD, who provided an overview of some of the many options.

New devices for measuring IOP

Dr. Freedman lauded rebound technology (Icare, Icare Finland) because there is no need to take patients to the operating room as often simply to check their IOP. Though both non-contact and rebound tonometry can be performed without topical anesthetic, rebound tonometry is more easily used to obtain a young child’s IOP in the office setting.

“Our studies [using rebound tonometry] with the Icare and the Icare ONE-not yet approved for commercial use in the United States-demonstrated in about two-thirds of cooperative children with known or suspected glaucoma that the tonometers measured IOP within 3 mm of the IOP measured with the gold-standard Goldmann applanation tonometer,” said Dr. Freedman, professor of ophthalmology and pediatrics, Duke Eye Center, Durham, NC.

“The Icare IOP measurements were usually higher than the Goldmann measurements by about 2 mm Hg, making rebound tonometry an excellent screening device,” she added.

An additional advantage of the Icare rebound tonometer, according to Dr. Freedman’s studies, is that it can be used as a clinical tool in the home setting by an adult family member to obtain IOP readings in pediatric patients with suspected glaucoma outside regular office hours.

Another tool (Icare PRO, Icare Finland) can be used with children in the supine position, but this device also is not yet approved for commercial use in the United States. It is Dr. Freedman’s hope that this instrument will be helpful for babies and in the operating room.

Surgical procedures

Angle surgeries-goniotomy and trabeculotomy, developed more than 50 years ago-still represent “pivotal developments” in the surgical care of pediatric patients with glaucoma, Dr. Freedman noted.

Goniotomy, first described in 1948, remains basically unchanged, which she explains is “a testament to the elegance of the procedure.”

Small modifications have been introduced over the years, such as use of a needle instead of a knife and use of an endoscopic approach in the presence of a cloudy cornea. The procedure also proven effective with uveitis-associated pediatric glaucoma, she added.

Regarding trabeculotomy, which was first reported in 1960, surgeons can use a standard trabeculotome to open 180° of the Schlemm’s canal, or can modify the technique to cannulate and complete a 360° trabeculotomy. This latter technique, first described using 6-0 Prolene suture, proves clinically very challenging in many cases.

“The illuminated microcatheter [iScience, iScience Interventional] has changed our approach somewhat in trabeculotomy,” Dr. Freedman said. “The illuminated microcatheter-originally developed for adult canaloplasty procedures-has made 360° trabeculotomy less technically challenging, expanding this procedure’s availability to more patients and more surgeons.”

The lighted tip of the microcatheter facilitates visualization of the catheter’s path in its travel around the circumference of Schlemm’s canal, as well as out of the canal in cases where it deviates into a collector channel.

The 360° trabeculotomy procedure is useful in patients with congenital glaucoma, as well as some cases of juvenile open-angle glaucoma and early-onset “aphakic” glaucoma.

Dr. Freedman shared a pearl for consideration during this procedure: When the microcatheter makes its way around Schlemm’s canal and can be retrieved, Dr. Freedman said she likes to pull one end of the catheter more than the other and leave the short end to be pushed back into the anterior chamber.

If the loop is pulled through, a fairly large opening is created that may allow iris prolapse, she explained.

Among glaucoma surgeries, one device (Trabectome, NeoMedix) is used during angle surgery in adults to remove the trabecular meshwork and Schlemm’s canal inner wall. Its usefulness in children, however, has not been proved. It is not recommended over traditional angle surgery, because of the limited angle opened, larger corneal opening required, and proven excellent alternatives, Dr. Freedman noted.

Schlemm’s canal stents (such as the iStent, Glaukos) are useful in adults but have no clear advantage in pediatric glaucoma, at least not yet.

Regarding filtration surgery, trabeculectomy has limited place in the care of pediatric glaucoma.   The use of mitomycin C has positively impacted trabeculectomy-especially in phakic eyes of children older than 2 years-but outcomes decline with time. Success is poor in infant and aphakic eyes, and all children are at lifelong risk of developing bleb leaks and infection when a functional trabeculectomy filtering bleb is present.

A small metal shunt for selected adult trabeculectomy cases (Ex-Press, Alcon Laboratories) also has no clear advantage in children. The site of trabeculectomy failure in children is not usually the sclerostomy, but rather the Tenon’s capsule and conjunctival layers, she explained.

Glaucoma drainage devices

Glaucoma drainage devices have been available for more than 30 years and prove very useful for refractory pediatric glaucoma cases, according to Dr. Freedman. 

Devices best studied for use in children include the:

• Molteno device (Molteno Ophthalmic Ltd.), introduced in the early 1970s.

• Baerveldt glaucoma implant (Abbott Medical Optics), introduced in the early 1990s.

• Ahmed glaucoma valve (New World Medical), also introduced in the early 1990s.

All three devices have undergone evolution of newer models in recent years, including the Molteno 3, characterized by a larger plate size compared with the original single-plate Molteno plate; the Ahmed FP7, a more flexible plate which is now in standard use in place of the Ahmed S2 device; and the recently introduced Ahmed M4, a coated device that aspires to minimize bleb encapsulation by using a coated reservoir.

Dr. Freedman recounted the results of her group’s retrospective non-randomized study of glaucoma drainage devices used for refractory cases of pediatric congenital glaucoma and aphakic glaucoma.   The study compared results achieved with the Baerveldt and Ahmed glaucoma drainage devices in these pediatric cases.

“We found that the initially very good success rates-for both devices and both diagnoses-declined to about 70% at 5 years postoperatively and just under 50% at 10 years postoperatively,” she said. 

Though such success rates would be considered excellent for elderly patients, it is Dr. Freedman noted that the longevity of pediatric patients with glaucoma might often require multiple surgical interventions over their lifetimes.

Regarding pediatric glaucoma implant surgery and which device to implant, the Ahmed device may be preferred over trabeculectomy in infant and aphakic eyes, she said.

“The valved Ahmed device is also preferred in cases where immediate IOP reduction is desired-as in infants with cloudy corneas who are being visually deprived-as well as for uveitis-related glaucoma, where flow limitation helps to avoid postoperative hypotony,” Dr. Freedman said.

The Baerveldt device is useful for older children when there is less urgency to reduce the IOP, and may be less likely to fail as a result of fibrovascular ingrowth into the valve chamber, a frequent cause of Ahmed failure in pediatric cases, she added.

“The jury remains out on use of mitomycin C and anti-vascular endothelial growth factor drugs in glaucoma drainage device surgery for children,” Dr. Freedman said. “In aphakic or pseudophakic eyes with a shallow anterior chamber, the tube should be placed away from the cornea in the pars plana.”

Endoscopic procedure

Endoscopic diode laser cyclodestruction is usually reserved only for refractory cases of pediatric glaucoma, and usually only for eyes that are already aphakic, she said. 

Dr. Freedman said she prefers to use this procedure as an adjunctive treatment after elevated IOP persists in eyes after glaucoma drainage device surgery, or in eyes where drainage device surgery is not anatomically feasible or poses special risks.

Special uses of the endoscopic feature of this device include identifying and treating ciliary processes that may be missed by externally applied transscleral cycloablation, as well as allowing endoscopic visualization (and removal by vitrectomy) of vitreous blocking a drainage device tube in the pars plana.

Sharon F. Freedman, MD

E: Sharon.freedman@duke.edu

Dr. Freedman has no financial interest in any aspect of this report.

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