Continuous IOP monitoring may be possible with implantable sensor

Issue: May 2005

ByJeanne Gonzalez

SNOWBIRD, Utah – An implantable microsensor that monitors IOP throughout the day may increase physicians’ understanding of glaucoma, according to Leon G. Partamian, MD.

Ramesh Ayyala, MD [photo]
Ramesh Ayyala

“A single IOP measurement in the office does not provide adequate information about IOP behavior,” Dr. Partamian said. IOP levels vary throughout the day, he noted, and current IOP measuring devices such as Goldmann tonometry create only a snapshot of the patient’s IOP.

Dr. Partamian and colleagues at the Jules Stein Eye Institute are developing a device that monitors IOP through two coils placed a distance apart on the cornea. The researchers observed accurate and consistent measurements with a prototype in pressure-chamber tests, he said.

“Our prototypes had resolutions of 1.2 mm Hg to 1.4 mm Hg with routine test equipment,” Dr. Partamian said, calling the results to date “promising.”

Following is a review of some of the other presentations at the AGS meeting.

PK vs. MAPPK and glaucoma

Penetrating keratoplasty was associated with a higher incidence of glaucoma than a microkeratome-assisted posterior keratoplasty procedure, according to a retrospective study. The posterior technique may be more benign because it reduces angle distortion, said Ramesh Ayyala, MD, here at the American Glaucoma Society meeting.

American Glaucoma Society meeting [logo] Dr. Ayyala and colleagues reviewed the records of patients who had undergone penetrating keratoplasty (PK) or microkeratome-assisted posterior penetrating keratoplasty (MAPPK). Fifteen patients underwent PK, and 16 underwent MAPPK, he said. The baseline IOP was 13 mm Hg in the PK group and 15 mm Hg in the MAPPK group. Follow-up was at 1, 3 and 6 months and 1 year.

At 1 month, mean IOP was 15.8 mm Hg in the PK group and 10.4 mm Hg in the MAPPK group. At 3 months, it was 21.67 mm Hg in the PK group and 15.87 mm Hg in the MAPPK group. At 6 months, it was 15.9 mm Hg in the PK group and 13 mm Hg in the MAPPK group. At 1 year, IOP was 17 mm Hg in the PK group and 13.75 mm Hg in the MAPPK group.

Dr. Ayyala said that by not disturbing the angle, MAPPK reduced the incidence of postoperative glaucoma. In the PK group, 30% of patients with no previous glaucoma developed glaucoma after the surgery, he said.

End-stage glaucoma treatment

Treatment of end-stage glaucoma, when calculated over a 2-year period, entails higher costs in the first year than the second, said John G. Walt, MD.

Dr. Walt and colleagues conducted a study to determine the direct costs of treating end-stage glaucoma during a 2-year period.

The costs associated with treating 47 patients with end-stage glaucoma at a single glaucoma clinic were evaluated, Dr. Walt said. The mean cost per patient for the first year of treatment was $2,606, and for the second year $1,496. Dr. Walt said surgery and low-vision rehabilitation accounted for much of the cost in the first year.

“Low-vision costs decreased from 50.2% of total costs [in year 1] to 39.6% in year 2,” he said. “All other costs also decreased from the first year to the second, except for drug costs, which remained relatively similar.”

During the 2 years, 13 surgeries were performed on the patients. The cost of drugs was the same over the duration of the study, Dr. Walt said.

Pediatric glaucoma detection

Childhood glaucoma is often overlooked by pediatricians and parents, and eye care practitioners should look for signs and symptoms of glaucoma when performing pediatric eye exams, said David Walton, MD.

Photophobia, tearing, corneal clouding, corneal enlargement, decreased visual acuity and progressive myopia are among the signs and symptoms that can be clues to the presence of pediatric glaucoma, Dr. Walton said.

“Childhood glaucoma is unusual, but it causes 10% to 20% of world blindness in children,” he said.

Photophobia is a symptom of glaucoma that may be seen in the first year of life, and it generally goes unnoticed by pediatricians and parents, he said. Often parents accept their child’s intolerance of light and do not believe it is a problem, he said.

Corneal opacities are probably the most common sign of glaucoma characteristically seen in newborn infants, Dr. Walton said.

Corneal enlargement can be a sign of elevated IOP, he said. Corneal enlargement is difficult to measure, but it can be estimated by comparing the size of the child’s cornea to that of the child’s mother.

Children taking steroids may be at increased risk of developing glaucoma, and their eyes may have a “cushioned” appearance and elevated IOP, he said.

He suggested using hand-held instruments to examine children more easily. Slit-lamps, tonometers and gonioscopes are among the instruments available in hand-held forms.

“The secret of care is in understanding and caring for the patient,” Dr. Walton said.

Preserving bleb after cataract

In patients with a functioning filtering bleb who are undergoing cataract surgery, steroid treatment may help preserve bleb function, said Edward J. Rockwood, MD.

Dr. Rockwood reported results in 224 eyes of 199 patients with functioning filtering blebs who underwent cataract surgery. He said a subconjunctival injection of triamcinolone acetonide was administered after cataract surgery. Topical prednisolone 1% was also dosed hourly. He told attendees that the corticosteroid treatments helped increase bleb survival.

The average time to bleb failure was 39.7 months (range, 0.1 months to 96 months), Dr. Rockwood said.

Filtering bleb failure was more likely to occur in the eyes of younger patients, patients with uveitis, those who underwent extracapsular cataract extraction and those who developed central vein occlusion or neovascular glaucoma, he said.

Bleb failure occurred in eight of 31 eyes (25.8%) that underwent extracapsular cataract extraction but in only 12 of 193 eyes (6.2%) that underwent phacoemulsification.

IOP and the use of IOP-lowering medications increased after cataract surgery, he said. Mean IOP increased from 11.3 mm Hg preoperatively to 15.4 mm Hg postoperatively, he said. Medications per patient increased from 0.1 to 0.7, he said.