Abstract
Purpose: :
To describe a computerized methodology to:A - Score visual fields (VF) with the AGIS system, and two Glaucoma Severity Scales {Brussini (GSS-Br), and Hodapp (GSS-BP)}.B - Generate VF parameters from theoretical threshold data.
Methods: :
Development required creation of:1. Computerized method to import large amounts of Humphrey VF (HVF) data.2. Method to estimate: Total Deviation (TD), Pattern Deviation (PD), PD Probability (PDPr), Mean Defect (MD), and Pattern Standard Deviation (PSD).3. Algorithms to calculate AGIS, GSS-BP, and GSS-Br scores.Humphrey VF (HVF) data from the Barbados Eye Studies were exported into a "calculator" written in Filemaker Pro 8. TD values were calculated as mean threshold-reference thresholds at each location. PD was adjusted for the seventh most sensitive point. For PDPr, 166 24-2 VFs and 102 30-2 VFs were used to determine appropriate cutoffs for categories of <5%, <2%, <1%, and <0.5% at each location. MD and PSD were calculated based on previously defined formulas. 166 24-2 HVF and 102 30-2 HVF were used to refine the calculation for theoretical threshold data. To calculate these variables, a normative threshold and variance database was made. AGIS, GSS-BP and GSS-BR scores were based on described rules.
Results: :
125 and 166 HVF were used to test TD and PD calculations respectively. Excellent correlation was confirmed for both, with a mean difference between actual and calculated values of less than 2 dB for all points. 17 HVF were used to test PDPr estimates. An exact match was calculated 74% of the time. Results were within 1, 2, 3,or 4 categories of the actual value 81.7, 87.4, 90.4 and 100% of the time respectively.17 30-2 and 22 24-2 VF were used to check MD and PSD calculations. Excellent correlation was observed with a mean difference of <3 between actual and calculated values for both MD and PSD. 10 random HVF were scored manually and with the calculator using actual data values for AGIS, GSS-Br, and GSS-BP systems. All were calculated with 100% accuracy.
Conclusions: :
We present a computerized method to accurately import HVF data, calculate HVF parameters of TD, PD, PDPr, MD and PSD based on theoretical threshold data, and calculate three different VF scores. This tool can be used to evaluate and compare the performance of these scoring systems under various conditions and to evaluate data from population studies.
Keywords: visual fields • computational modeling