Patients with keratoprosthesis may be at risk for glaucoma progression

In a series of 38 patients, 89% displayed glaucoma and 21% displayed glaucoma progression.

Patients who undergo implantation of Boston keratoprosthesis type 1 may be at higher risk for glaucoma development or progression than previously believed, a study found.

Treating ophthalmologists should exercise caution and closely monitor IOP in Boston keratoprosthesis type 1, or K-Pro, recipients, Julia C. Talajic, MDCM, said at the Association for Research in Vision and Ophthalmology meeting in Fort Lauderdale, Fla.

“The presence of glaucoma is almost ubiquitous in this population, and patients can rapidly progress to end-stage glaucoma,” Dr. Talajic said. “Close follow-up of such patients with serial visual field testing is therefore paramount, and low thresholds should be used to treat suspicion of even slightly elevated intraocular pressure in K-Pro patients.”

The most recent iteration of the K-Pro has been shown to be a safe, viable alternative to penetrating keratoplasty in selected cases, Dr. Talajic said.

“The Boston keratoprosthesis is increasingly recognized as a viable treatment for corneal blindness that is poorly amenable to penetrating keratoplasty,” she said. “With the latest K-Pro prototype, traditional complications such as extrusion, corneal melt and endophthalmitis have become less common. However, an old obstacle has become increasingly relevant, that of advanced and even absolute glaucoma.”

Patients and parameters

A chart review included 38 eyes of 38 consecutive patients who underwent K-Pro implantation in 2008 and 2009. Mean patient age was 61 years; most patients were male. Mean axial length was 23.6 mm.

Of the 38 patients, 37% had undergone previous glaucoma surgery. Preoperatively, 76% of patients had glaucoma, and 50% were taking pressure-lowering medication.

Twenty-five patients had undergone previous penetrating keratoplasty. The most common diagnoses among these 25 patients were aniridia, chemical burn and post-traumatic scarring. Aniridia was the most common diagnosis among the remaining 13 patients who underwent primary K-Pro surgery.

Improvement in visual acuity was defined as a progression from counting fingers to Snellen visual acuity of 20/200 or better.

Definite glaucoma progression was defined as worsening of the visual field or the need for glaucoma surgery postoperatively. A worsening visual field was defined as a 15· constriction of the pattern characteristic of glaucoma on Goldmann visual fields or a 10-decibel decrease in mean deficit on Swedish interactive threshold algorithm-fast visual fields.

Preoperatively, a majority of patients had visual acuity worse than counting fingers.

One surgeon performed all K-Pro implantations. Phakic patients underwent extracapsular cataract extraction and received an aphakic K-Pro. In pseudophakic patients, unstable lenses were explanted and the patients were left aphakic. Anterior vitrectomy was performed in patients with no posterior chamber IOL in place. Non-aniridic patients underwent goniosynechialysis, iridectomy and pupillary sphincterotomy.

Postoperatively, all patients received moxifloxacin and prednisone acetate. Investigators assessed visual acuity, digital IOP and cup-to-disc ratio and also performed serial visual field testing at the discretion of the treating physician. Mean follow-up was 16.5 months.

Postop glaucoma and intervention

Postoperatively, 89% of patients had glaucoma and 76% were taking pressure-lowering medication. An increase in IOP-lowering medications from preoperative baseline was required by 63% of patients. The average number of drops per patient increased from 0.89 preoperatively to 1.97 postoperatively.

Definite glaucoma progression was seen in eight patients (21%), five of whom lost fixation.

About one-fifth of patients suffered a hypertensive spike that was self-limited and mitigated with medications. Forty percent of patients had a cup-to-disc ratio of 0.85 or greater.

Five patients underwent surgery for uncontrolled IOP. Three patients underwent Ahmed tube implantation (New World Medical). Two of those three patients had vitreous strands obstructing the tube and underwent pars plana vitrectomy and endocyclophotocoagulation. The third patient developed a corneal melt and received a corneal patch graft.

The fourth of five patients requiring surgery for uncontrolled IOP underwent transscleral photocoagulation. The fifth patient, who had a pre-existing shunt that was blocked by vitreous, underwent vitrectomy and subsequently developed a choroidal detachment.

A spontaneous suprachoroidal hemorrhage developed in another patient with a pre-existing tube shunt.

Aphakic patients increased from 24% preoperatively to 87% postoperatively.

“This is owing to the fact that six unstable lenses were explanted and 18 phakic eyes were made aphakic,” Dr. Talajic said.

Data showed that visual acuity improved in 87% of patients.

“However, we know that the most recent best corrected visual acuities diminished with regard to the best postoperative visual acuity,” Dr. Talajic said. “Patients whose visual acuity did not improve include those with pre-existing terminal glaucoma, previous retinal detachment and subsequent macular atrophy, myopic maculopathy, another patient with probable pre-existing terminal glaucoma.”

Dr. Talajic said further study is required to determine the appropriate timing of glaucoma surgery in K-Pro patients. – by Matt Hasson and Courtney Preston

• Julia C. Talajic, MDCM, is an ophthalmology resident at the University of Montreal. She can be reached at email: julia.talajic@umontreal.ca.
• Disclosure: Dr. Talajic has no relevant financial disclosures.