Traquair described the topography of visual field sensitivity as a “hill” or “island” of vision. Achromatic automated perimetry (AAP) demonstrates this shape of the visual field in photopic conditions. Techniques claimed to target the magnocellular pathway (frequency doubling perimetry, FDP) and those using a stimulus targeting the koniocellular pathway (short wavelength (or blue on yellow) automated perimetry, SWAP), might produce one that is different. The authors compared the visual field topography from FDP with those of SWAP and AAP, to investigate whether there were significant differences in their shape.Method:
A sample of 51 patients with previously confirmed normal perimetry were recruited; either low risk glaucoma suspects or normal controls. AAP, SWAP, and FDP perimetry was performed in random order on the same day. The topography of each field was analysed to determine its average shape and to compare results in the same individuals.Results:
The topography of the visual field produced by each perimeter differed significantly. While all three had maximal sensitivity centrally, over the 24 degrees from the centre to the periphery, mean sensitivities decreased by 4.9 decibels (dB) for AAP and 7.3 dB for SWAP, while FDP sensitivities by just 1.8 dB over 20 degrees (the extent of the FDP field). FDP mean sensitivities decreased by approximately 0.3 dB with every 10 year increase in age, compared with 1 dB for AAP and 2 dB for SWAP.Conclusion:
While the topography of the SWAP (koniocellular) field is steeper than corresponding AAP fields, that of the FDP (magnocellular) visual field was considerably flatter. The difference in this shape may reflect retinotopic or cortical mechanisms, which are specific to the magnocellular pathways.