Abstract
Purpose::
To evaluate the inter-visit, inter-observer repeatability of the Glaucoma Probability Score (GPS) and to compare its ability to monitor glaucomatous progression with established visual field (VF) progression strategies.
Methods::
1) Heidelberg Retina Tomograph (HRT) ‘Classic’ inter-visit, inter-observer test-retest data from 74 subjects (Br. J. Ophthalmol. 2005;89;1427-1432) were analysed in HRT-3 Explorer software to generate the global GPS. Variance was related to the GPS, so repeatability coefficients (RCs) were calculated for 3 GPS bins (0-19%, 20-79% and 80-100%).2) 198 OHT and 21 control subjects were examined longitudinally (1993-2001) using regular HRT (‘Classic’) and VF testing. 5 or more HRT and VF tests were available for each subject. GPSs were generated in HRT-3 Explorer software. Linear regression of global GPS over time was performed for each subject, with significance p < 0.05. Criteria for estimates of specificity were: 1) significant deterioration of GPS over time in controls and 2) significant improvement of GPS over time in all subjects. The number of OHT subjects significantly deteriorating was compared to a VF pointwise linear regression strategy with similar specificity.
Results::
There was good GPS repeatability for the 0-19% and 80-100% bins, at RC = 0.4% and 4.3%, respectively. However, in the 20-79% bin, repeatability is poor with RC = 13.5%.Estimated specificity (95% confidence intervals) was 95.2% (76.1 - 99.9%) for GPS criterion 1 and 96.8% (93.2 - 98.6%) for GPS criterion 2. 25 OHT subjects were identified as progressing. VF progression was identified in 11 of these subjects. 26 OHT subjects were progressing by VF alone.
Conclusions::
GPS scores between 20 and 79% are variable and should be interpreted with caution. Despite this, linear regression of GPS over time achieved a good specificity, with positive detection rates similar to other HRT progression algorithms at the same level of specificity (Invest Ophthalmol Vis Sci. 2006;47:2904-2910). Agreement (proportions progressing by GPS and VF) was also similar to previous reports.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • optic disc