Background: Two commonly used perimeters in Australia are the Humphrey Field Analyzer II (HFA) and the Medmont Automated Perimeter (MAP). Each device describes the visual field in terms of numerical values called 'global indices', however these values are not interchangeable between devices. This study was designed to compare directly the global indices of HFA and MAP visual fields.
Methods: 63 subjects who were glaucoma suspects, ocular hypertensives, glaucoma patients, or normal controls were recruited selectively. Each patient was tested with the MAP and HFA. Global indices were then compared between tests. These included Mean Deviation (MD) and Pattern Standard Deviation (PSD) from HFA and Average Defect (AD) and Pattern Defect (PD) from MAP.
Results: Results of MD and PSD were strongly correlated with those of AD and PD respectively. The relationship between them could be described in terms of two polynomial equations: AD = 0.94 + 1.31(MD) + 0.02(MD) 2 and PD = 2.21(PSD) - 0.05(PSD)2 - 0.006. These nonlinear relationships may be the result of differences in testing method (test stimulus spectrum, number of testing locations or background luminance) or differences in the way each global index was calculated.
Conclusion: The AD and PD results obtained from the MAP may be substituted for the MD and PSD of the HFA after an appropriate conversion.
- Automated Perimetry
- Global Indices