Comparison of achromatic automated perimetry, short-wavelength automated perimetry and frequency doubling technology perimetry in the diagnosis of early glaucoma

Early glaucomatous damage is mainly due to a loss of large ganglion cells (M cells and/or larger P cells). Frequency doubling technology (FDT) and short-wavelength automated perimetry (SWAP) are recent kinds of automated perimetric tests considered able to isolate the function of M and the larger P ganglion cells, respectively. In the early stages of glaucomatous optic nerve damage, achromatic automated perimetry (AAP) can be normal, while FDT or SWAP can reveal early losses produced by the disease. The aim of this study is to compare the sensitivity of AAP, SWAP, and FDT in the detection of early visual field defects and to verify the involvement of M cells and/or larger P cells in early glaucomatous damage. The authors selected a group of 22 glaucoma suspect patients with normal AAP, and an intraocular pressure (IOP) between 22 and 27 mmHg and tested them with SWAP and FDT. They observed that the defects detected by SWAP and FDT were more extensive than with AAP, the defects detected by FDT were more severe than with SWAP and only one patient showed both SWAP and FDT deficits. In conclusion, FDT and SWAP seem to be more sensitive than AAP in detecting early glaucomatous visual field damage. Different patients present different aspects of Mand/ or P-cell loss, and M-cell damage is probably the most common. FDT can consequently be considered a sensitive perimetric diagnostic test in early glaucoma diagnosis.