FDT and VFs.

I decided I should finally look into what FDT actually is, since the perimeter at work is different from the typical Humphrey Visual Field Analyzer I've seen before. Traditionally perimetry is done by presenting lights in the patient's periphery while they are fixated on a central target to see whether their retinal sensitivity is good enough to detect it or not. The FDT Perimeter uses a vertical sine wave grating as a stimulus:

It flickers at 25 Hz, with variable target size and contrast. And at a high temporal frequency, the spatial frequency appears to be doubled - thus, Frequency Doubling Technology, or FDT.

Points of interest:
1.

The large low spatial frequency targets are not significantly affected by refractive errors up to 6D, so optimal near correction is not needed

2. FDT perimetry is based on this phenomenon:

when an achromatic sinusoidal grating of low spatial frequency undergoes counterphased flickering at a high temporal frequency, the apparent spatial frequency of the grating appears to be doubled.

3.

FDT offers many advantages in that it is easy to administer and interpret, liked by most patients, not greatly affected by refractive error and cataract, has high test-retest reliability, offers rapid screening tests, and has different full threshold programs.