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Glaucoma valve, keratoprosthesis combination yields high retention rate
The combined procedure is not associated with more complications or failure of the KPro.
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Combined implantation of a glaucoma drainage device and a keratoprosthesis enabled surgeons to restore vision and manage IOP with a high success rate, according to a study.
The study authors discussed concurrent implantation of an Ahmed glaucoma valve (New World Medical) and a Boston type 1 keratoprosthesis (KPro) in the Journal of Glaucoma.
“Based on our preliminary data comparing a combined procedure vs. KPro alone in patients with glaucoma, eyes with a GDD placed at the time of KPro required less additional glaucoma surgery and had better IOP control,” Simon K. Law, MD, PharmD, told Ocular Surgery News. “The most significant finding is that a combined procedure is not associated with more complications or failure of the KPro.”
Law noted that the prevalence of glaucoma in eyes diagnosed with the disease before and after KPro implantation ranges from 36% to 89%.
“We have to understand that eyes that required KPro surgery were quite sickly to begin with, had undergone one or more corneal transplants, and may have had trauma, different ocular diseases and surgeries,” Law said.
Errant cells, iris pigment, inflammation, steroid use and compromised aqueous outflow can increase the risk of glaucoma after KPro implantation, he said.
“Some believe that the increased scleral rigidity and alteration of the biomechanical forces of the eye after KPro may render the optic nerve more susceptible to the change of eye pressure,” he said. “Another difficulty in managing the glaucoma in these eyes is the inability to accurately estimate the eye pressure because of the scarred cornea before the KPro surgery and the KPro itself, so that estimation of eye pressure is limited to digital palpation.”
Surgical technique
“We find that it is easier for surgeons to follow the basic technique of implantation of GDD when implanting it concurrently with KPro procedure. There are some important steps to remember,” Law said.
For example, the glaucoma drainage device (GDD) should be implanted before the cornea is opened.
“It is much safer to implant the GDD when the eye is formed,” Law said.
The surgeon should use ultrasound biomicroscopy or optical coherence tomography to visualize anterior segment structure and determine the quadrant in which to insert the tube, he said.
Viscoelastic material should be injected into the eye, preferably through the needle track, to maintain relatively normal pressure and avoid a sharp drop in pressure.
The tube should be left at least 4 mm inside the eye so that it clears the pupillary margin and can be identified after the cornea is opened. The tube should be trimmed no shorter than 2 mm inside the eye because tubes typically retract up to 2 mm when the globe is formed again and pressurized, Law said.
Patients and measures
The retrospective study included 29 eyes of 29 patients who underwent implantation of an Ahmed valve followed by KPro insertion. Mean follow-up was 34.4 months.
Secondary angle closure glaucoma was identified in 24 eyes (82.8%). Failed repeat corneal grafts were identified in 21 eyes (72.4%).
Outcome measures were visual acuity, number of glaucoma medications and complications.
Automated visual field testing, stereoscopic optic disc photography, confocal scanning laser ophthalmoscopy and retinal nerve fiber layer analysis were performed after surgery.
Retention, vision and complications
Study results showed that 82.8% of KPro devices were retained at the mean follow-up point.
The device was removed from three eyes because of corneal necrosis, one eye because of endophthalmitis and one eye because of spontaneous extrusion.
Retroprosthetic membrane was identified in 13 eyes (44.8%). Eleven eyes (37.9%) underwent membranotomy with Nd:YAG laser, and two eyes (6.9%) underwent manual membranectomy.
Corrected distance visual acuity improved in 17 eyes (58.6%), remained unchanged in seven eyes (24.1%) and worsened in five eyes (17.2%).
Mean number of glaucoma medications decreased from 2.1 before surgery to 1.5 at 3 months postoperatively, 1.6 at 6 and 12 months, 1.7 at 24 months and 1.2 at 36 months. The reductions were statistically insignificant.
One eye required endocyclophotocoagulation for persistent glaucoma.
“Previous studies have shown that GDD at the time of KPro may be associated with erosion, which can lead to infection and associated devastating outcomes,” Law said. “However, in our series, we found that the erosion was all associated with prior GDD and none was associated with the concurrent GDD at the time of KPro. Similar observation was made in other studies.” – by Matt Hasson