Estimating the rate of progressive visual field damage in those with open-angle glaucoma, from cross-sectional data

Abstract

Purpose: To estimate the rate of visual field progression in open-angle glaucoma (OAG) subjects, by using data from population-based cross-sectional studies.

Methods: Subjects with OAG were identified in nine surveys of randomly sampled populations using standard criteria for glaucomatous optic neuropathy. Subjects were of European, African, Chinese, and Hispanic ethnicity. The measure of OAG damage was the mean deviation (MD) of an automated visual field test (Humphrey Field Analyzer; Carl Zeiss Meditec, Inc., Dublin, CA). The rate of progression was the mean of all subjects' damage in the worse eye divided by an average time since onset. Time since onset was estimated from age-specific prevalence rates.

Results: A total of 1066 subjects with OAG contributed visual field data. The mean worsening in decibels per year was: European-derived, -1.12; Hispanic, -1.26; African-derived, -1.33; and Chinese -1.56 (difference among ethnicities, P = 0.16). The mean duration of disease was lowest among Chinese persons at 10.5 years (95% CI: 8.8-12.6) and was highest in African-derived subjects at 15.4 years (95% CI: 14.6-15.9). The progression rate was not consistently related to age or gender. By combining disease duration and progression rate, the model predicted that 15% or fewer of the worse eyes would reach the end of the field damage scale in the patient's lifetime.

Conclusions: The estimates of typical worsening per year in the worse eye among subjects with OAG suggested slightly more rapid progression than in some clinic-based studies. The rate did not differ significantly by ethnicity or gender, but was worse in those with known, treated OAG and in pseudophakic subjects.

Figure 1

Age-specific prevalence by ethnicity. Prevalence curves generated by Quigley and Broman from 34 population-based OAG prevalence surveys.

Figure 2

Age-specific incidence by ethnicity. Incidence estimates (solid lines) for OAG in four ethnicities generated from age-specific prevalences in Figure 1. The 95% CI for our estimates (dashed lines) overlap the data from two individual direct measurements of incidence in population surveys (circles and flags, mean and 95% CI). These are the Melbourne VIP study (shown in European-derived curve, top left) and the Barbados Eye Study data (shown in African-derived curve, top right).

Figure 3

Duration curves by ethnicity. We calculated the average age at OAG onset for each age, to arrive at a mean duration of disease at each age from 30 years onward. The mean value (solid line) and 25th, 75th, and 95th percentiles are shown for this value. The mean duration of disease reached a maximum of about 15 years in the ethnicity with the highest value (African-derived). See also Table 2.

Figure 4

Progression rate by age for four ethnicities. (○) Mean progression rate estimate for individual subjects; gray line: mean progression rate for each ethnicity. Black line: the change in progression estimate by age with its 95% CI. The progression rate was worse (more minus) with age in European-derived, slower with age in African-derived, while unchanged with age in Chinese and Hispanic subjects.