The above instrument is used to test visual field and the field print-out is as shown on the right. a. What is this instrument? b. What is the principle behind this instrument?
a. What is this instrument?
b. What is the principle behind this instrument?
Answer to a a. Frequency doubling perimetry. Answer to b b. The instrumment specifically tests for visual field loss due to non-linear M-cell neuron death especially from glaucoma. The larger diameter M cell neurons (responsible for low-contrast, high temporal frequency (or motion) stimulus detection) constitute approximately 10% of the total number of retinal nerve fibers. It has been found that a particular M-cell neuron sub-set comprising a third to a half of the M-cell neurons (called "non-linear" M-cells) are usually the first to die in glaucoma, and this unique pathological characteristic established the basis for frequency doubling testing.
