Before their operation, the patients were, on average, on 3.3 medications and had an intraocular pressure of 22.72 mm Hg. The surgical team modified the adult investigational device exemption protocol. They performed general anesthesia, a smaller limbal incision in the superior-nasal quadrant of the affected eye, and precision injection of 40 µg of mitomycin-C in the superior-nasal quadrant rather than the use of sponges.
The team noted no complications during the operation. They found that the flow of the aqueous humor from the posterior lumen of the device happened immediately upon entry of the device into the anterior chamber; little, if any, aqueous humor flows around the device.
The team followed these children for at least one year after their operation. At 12- to 18-month follow-ups, nine eyes (75%) showed success. Three eyes (25%) failed and required additional surgery.
After one year, the nine successful eyes had a 45% drop in their intraocular pressure (from 21.6 ± 4.9 mm Hg pre-operation to 11.9 ± 3.8 mm Hg). Also, seven patients were taking no medications, and two required two medications (fixed-combination dorzolamide-timolol).
Although promising, Brandt notes there are significant limitations to the study. It was too small and heterogeneous — in terms of age, diagnosis, and previous surgery — to generalize to all children. And one of the more common forms of childhood glaucoma, glaucoma after cataract surgery, was not encountered in this initial cohort.
Also of note was that preoperative intraocular pressure in the success and failure groups overlapped. The data are too sparse to evaluate the role of starting intraocular pressure in long-term outcomes.
Learning to place microshunts in pediatric eyes
Brandt had experience placing the microshunt in adult eyes, but he observed a significant learning curve when performing the procedure in pediatric eyes.
“The device is designed for an entry site 3 mm posterior to the limbus to assure proper scleral seating of the microshunt and a short 1.5 mm length of the implant in the anterior chamber. The limbus can be challenging to identify in children, particularly in eyes with significant buphthalmos, or anterior segment dysgenesis where limbal landmarks are smeared or indistinct,” Brandt said.
Bleb-forming minimally invasive glaucoma surgery (MIGS) devices might be an attractive interim step for refractory childhood glaucoma before moving to the more extensive surgical dissection and risk associated with trabeculectomy with mitomycin-C or plate-based glaucoma drainage devices.
The team is planning a multicenter, prospective clinical trial of this novel microshunt. It will be the first clinical trial of the device in children.
Read the study.