To evaluate short-term and long-term fluctuations and learning effects in healthy
subjects tested with the frequency doubling technique, which is based on a low spatial
frequency and a high temporal frequency stimulus.
Twenty-three healthy adult subjects were consecutively recruited from volunteers,
and 20 subjects finished the study. All the visual fields were assessed by the frequency
doubling technique, program C-20, full threshold. The frequency doubling technique
presents stimuli on a black-and-white video monitor with specialized control circuitry
interfaced to a microprocessor. During program C-20, full threshold, 17 points are
tested, one round point centrally and 16 square ones in the periphery up to 20 degrees
of eccentricity. Each stimulus consists of a 0.25-cycle/degree sinusoidal grating
undergoing a 25-Hz counterphase flicker. One eye of each patient was chosen at random.
Each subject was tested once in the first session, three times in the second session,
and once in the third and fourth sessions. Both short-term and long-term fluctuation
were studied either as the average fluctuation value of all the points tested or as
a point-to-point fluctuation. To study the learning effect, the results of the first
session were compared with those of the second, the third, and the fourth sessions.
The average mean sensitivity of the three examinations of the second session was 30.4
+/- 1.24 dB, and the average short-term fluctuation of all the subjects was 2.16 +/-
0.5 dB. The short-term fluctuation of each point tested ranged from 1.4 to 3.4 dB.
The average mean sensitivity for all the sessions was 32.4 +/- 1.14 dB, with an average
long-term fluctuation of 3.23 +/- 0.5 dB, and the long-term fluctuation of each tested
point ranged from 2.5 to 4.4 dB. A mild learning effect was found between the first
section and the others.
Short-term and long-term fluctuations were similar to those known to occur with the
conventional threshold perimetry when they were compared with the literature data.
A learning effect was also observed and should be taken into account for the clinical
use of this test.