Canadian researchers have confirmed once again that a modest reduction in intraocular pressure can significantly lower visual field loss in patients who have progressive glaucoma.
A 20% decrease in median intraocular pressure from 18 mm Hg to 14.8 mm Hg led to a significant change in the mean deviation (MD) rate from −0.36 to −0.11 dB/year (P<0.02), which represented a reduction in rate of progression by a factor of three, according to Balwantray C. Chauhan, PhD, of Dalhousie University in Halifax, Nova Scotia, and colleagues.
"In some patients, this amelioration may not be clinically significant; however, over 20 years the difference in total MD change resulting from these two rates is 5 dB," the researchers wrote online in the Archives of Ophthalmology.
"In younger patients with more advanced damage, this difference is likely to be important," they added.
Various reports on progression of visual field loss in patients with glaucoma have found rates of MD change from 0 to −2.5 dB/year.
To assess the effects of reductions in intraocular pressure and impact of risk factors on rates of MD change, Chauhan and colleagues analyzed data from 216 patients enrolled in the multicenter Canadian Glaucoma Study.
Patients with open-angle glaucoma were followed with a standardized protocol involving automated perimetry, and disease progression was suspected when eight or more locations in the total deviation change probability map were flagged and four or more were clustered locations in a single hemifield.
If a second perimetry test confirmed progression, the patient was considered as having reached an endpoint, and received additional intraocular pressure reduction.
Median age at baseline was 65.2 years, and men numbered slightly more than women.
A total of 70.8% of patients had no endpoints, 20.1% had one, 7.4% had two, and 0.9% had more than two.
The median MD rate in patients with at least one endpoint was −0.35 dB/year, while the rate in patients with no endpoints was 0.05 dB/year (P<0.001).
MD rates were significantly different among patients with zero, one, and two endpoints (P<0.001), indicating that a worse initial rate was associated with more endpoints.
In addition, the median MD rate worsened by about −0.3 dB/year per endpoint. "This finding is of significance as it indicates that a worse initial rate of visual field change is related to subsequent progression despite additional [intraocular pressure] lowering after an endpoint," the researchers observed.
These researchers had previously identified four risk factors for progression, which were female sex, older age, abnormal anticardiolipin antibody, and higher mean follow-up intraocular pressure.
In this analysis, MD rates for the ten patients who had abnormal anticardiolipin antibody levels were significantly worse, at a median of −0.57 dB/year, than for those with normal levels, whose median rate was −0.03 dB/year (P=0.004).
Worse rates also were weakly but significantly associated with increasing baseline age (Spearman ρ= −0.190, P=0.005).
Rates were not different, however, between men and women or according to intraocular pressure.
A possible explanation for the differences seen with risk factors in this study were that this analysis was univariate and did not account for differences in follow-up times, according to the authors.
They noted that the Canadian Glaucoma Study is limited by the lack of a control group, so other unmeasured factors such as regression to the mean may have contributed to the observed amelioration of MD rates.
Using visual field change as the only criterion for progression is another limitation, because optic disc changes also may contribute.
Nonetheless, the researchers concluded that patients with early visual field damage who do not reach an endpoint and maintain the intraocular pressure at about 16 mm Hg have generally stable disease, and a modest further reduction in pressure in patients who do reach an endpoint can favorably influence subsequent MD rate.