The following differences are known. Further differences are possible.
Die results of kinetic examinations cannot be displayed by PeriData
The manufacturer has not released the normal values for blue-on-yellow examinations. For this reason, PeriData shows only the threshold values and the grayscale.
Concerning examinations with SITA strategy, the perimeter does not send false positive trial scores. Concerning examinations with SITA FAST strategy, the perimeter does not send neither false positive nor false negative trial scores. -- Actually, these trials are not performed. The percentage on the original perimeter printout is an estimated value.
Only very old versions (older than A1.2) of the HFA 2: The results of defect depth measurements are transmitted incompletely. The displayed values may be wrong.
PeriData uses different normal value tables than the perimeter, because the original tables have not been released. PeriData calculates with decimals and uses a different rounding formula than the perimeter software. The differences are small (about 1 to 2 dB).
PeriData uses the original formula of MD (mean of all total deviation values). The perimeter software calculates MD while weightening each value: central values are weightened higher and values outside 20 degree are weightened lower. Therefore, the HFA-MD can be greater (deeper in the minus range) in case of central scotoma and smaller in case of ring scotoma.
We never observed a change in categorizing a visual field as normal or pathological by these differences in calculation.
Trend analysis is not influenced at all because the bias is uniformly over the whole series.
The number of storable test positions (test points) is limited to 208. Examinations with more points (Fullfield screening test) are not completely stored. In the display, some points are missing.