Study confirms modest IOP reduction can improve visual field results

Study patients with abnormal anticardiolipin antibody levels and advanced age had faster visual field change.

Advanced age and anticardiolipin antibody levels indicate more rapid glaucoma progression, and even a modest reduction in intraocular pressure significantly slowed the rate of visual field decline, the Canadian Glaucoma Study found.

Primary Care Optometry News Editorial Board member Murray Fingeret, OD, said the recent finding does not change the prevailing wisdom for treating glaucoma.

“This study reinforces what we’re already doing. Reducing IOP makes sense, and if you lower it enough you can prevent patients from getting significantly worse,” Dr. Fingeret commented on the study in an interview.

The study

The prospective, multicenter interventional cohort study followed 216 open-angle glaucoma patients (median age 65.2 years) at 4-month intervals. Patients were monitored for progression using event-based SAP progression criteria to define an end point based on the glaucoma change probability analysis. Progression was suspected when eight or more locations in the total deviation change probability map, with four or more clustered locations in a single hemifield, were flagged and an end point was reached, the authors said. The median mean deviation (MD) rate worsened by approximately -0.3 dB/y per end point, the authors said.

Rates of MD change for abnormal anticardiolipin antibody (ACA) levels, age, female sex and mean follow-up IOP were computed in this study using regression analysis.

Results

Of the study population, 113 men and 103 women were included in the analysis. One hundred and fifty-three patients had no end point, 45 patients had one end point, 16 patients had two end points, and two patients had three end points. Due to the limited number, patients with three end points were not examined further.

The median MD rates in patients with zero and one end points were statistically significant at –0.35 dB/y (IQR, -0.76 to -0.12 dB/y) and 0.05 dB/y (IQR, -0.14 to 0.35 dB/y), respectively.

There were no differences in the sex ratio among patients with zero, one or two end points. Higher age was associated with one or two end points, and neither baseline visual acuity nor baseline target IOP was related to the number of end points, the authors said.

The MD rates for the 10 patients with abnormal ACA levels were significantly worse than the remaining patients with normal levels (median -0.57 dB/y, IQR -2.37 to -0.09 dB/y and median -0.03 dB/y, IQR -0.33 to 0.33 dB/y, respectively).

“The present analyses demonstrate that [patients with glaucoma and abnormal baseline ACA levels] have a notably more rapid rate of visual field deterioration compared with patients of normal ACA levels,” the study authors said. While this finding is significant, the small percentage of patients with abnormal levels limited study conclusions, they said.

Treatment was initiated once visual field progression was confirmed. Progressing patients received an additional 20% or greater IOP reduction from baseline target IOP using a stepwise treatment protocol of monotherapy, adjunct topical therapy, argon laser trabeculoplasty and/or systemic carbonic anhydrase inhibitors and trabeculectomy.

Median IOP decreased from baseline target IOP of 18 mm Hg to 14.8 mm Hg in patients at one end point, representing a 20% decrease for individual patients. According to the authors, the median reduction of 3.1 mm Hg resulted in a significant decrease in the median slope from -0.36 dB/y to -0.11 dB/y, which could be a significant advantage for younger patients with advanced damage. Median IOP decreased in patients with two end points from 16.3 mm Hg to 14.5 mm Hg, representing an 18% median decrease in individual patients.

According to the authors, a modest additional IOP reduction in patients with an end point has a significant effect on the subsequent MD rate, though the authors cannot speculate whether even greater IOP reduction would have an even more beneficial effect.

Take-home message

“For the most part, the results of this study go hand in hand with previous studies of the same form. Lowering IOP reduces progression,” Dr. Fingeret told PCON. “What’s unique in this study is the use of trend analysis to determine the rate of change and see if it was influenced based upon IOP reduction. And it was.” – by Stephanie Vasta

Reference:

• Chauhan BC, Mikelberg FS, et al. Canadian Glaucoma Study Group. Canadian Glaucoma Study: 3. Impact of risk factors and intraocular pressure reduction on the rates of visual field change. Arch Ophthalmol. Published August 9, 2010. doi:10.1001/archophthalmol.2010.196.

• Murray Fingeret, OD, is chief of the optometry section at the Department of Veterans’ Affairs Medical Center in Brooklyn and Saint Albans, N.Y., and a professor at SUNY College of Optometry. He is also a member of the Primary Care Optometry News Editorial Board. He may be contacted at St. Albans VA Hospital, Linden Blvd. and 179th St., St. Albans, NY 11425; (718) 298-8498; fax: (516) 569-3566; murrayf@optonline.net.