Quantifying adaptation and fatigue effects in frequency doubling perimetry.
OBJECTIVE
The second eye tested in frequency doubling perimetry has higher thresholds (reduced sensitivity) than the first. The authors investigated how this "second-eye effect" evolves over time and studied systematic changes in threshold in the first eye.


METHODS
Thresholds were measured in four subjects for 5 degrees -square, 0.5-cyc/deg sine wave gratings counterphase-flickered at 18 Hz, using a "method of a thousand staircases" to track changes in thresholds at 10-second intervals. Stimuli appeared in 1 of 5 interleaved horizontal locations. Subjects adapted binocularly (background, 45 cd/m(2)) for 5 minutes before performing a 5-minute test with one eye (the "first eye") followed immediately by the other (the "second eye"). These results were compared with baseline monocular thresholds measured over 3.5 minutes according to a conventional staircase procedure. In addition, two subjects repeated the main experiment with a translucent, rather than opaque, patch.


RESULTS
On average, second-eye thresholds were raised by 6 dB (0.3 log) at the beginning of the test and were reduced to 4 dB toward the end. Little change was observed in the magnitude of the second-eye effect as a function of eccentricity. A significant "first-eye effect" was also observed in which thresholds increased by approximately 2 dB as the first-eye test progressed. Translucent patching largely abolished first- and second-eye effects, indicating neither was the result of fatigue.


CONCLUSIONS
Steady adaptation in both eyes is important for obtaining stable perimetric thresholds. Unless appropriate tests are performed, the effects of adaptation could easily be mistaken for those of fatigue.
Anderson
Andrew John
AJ
Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia. aaj@unimelb.edu.au
McKendrick
Allison Maree
AM
D000221:Adaptation, Ocular / Q000502:physiology*; D000328:Adult; D001248:Asthenopia / Q000503:physiopathology*; D006801:Humans; D008027:Light; D008875:Middle Aged; D012684:Sensory Thresholds / Q000502:physiology; D058609:Visual Field Tests; D014794:Visual Fields