Frequency Doubling Technology perimetry (FDT) is a new non-conventional
visual field testing method, which selectively analyzes the My ganglion cells.
The test is fast and easy, but it may be difficult to interpret the results and
to classify the severity of damage. Standard Automated Perimetry (SAP) results
can be classified into stages of increasing severity according to different
methods (analysis of number of depressed points, visual field indices, Glaucoma
Staging System, etc.).
We classified 100 FDT tests from patients with both ocular hypertension
and chronic glaucoma in four groups (normal tests, early defects, moderate
defects, and severe defects). Three different approaches were used: a) clinical
analysis of FDT probability map; b) FDT DM and DSM indices, graphed on a 2-axis
nomogram; and c) an Abnormality Score, based on both the statistical
significance and the spatial location of depressed points. The same patients
were also tested with SAP (30-2 Humphrey threshold program), and these results
were also classified in four groups using the Glaucoma Staging System (GSS).
All three approaches gave good results in comparison to the GSS
classification, but the nomogram (method b) was the easiest and quickest
system. Both the clinical evaluation of probability map (method a) and the
Abnormality Score (method c) were precise, but it took more time to assess and
calculate individual tests.
We believe this nomogram could be useful to differentiate the damage
into stages, and to separate the normal tests from abnormal, making the
interpretation of FDT results easier.