Background: In frequency-doubling technology (FDT) perimetry, the second eye tested has reduced sensitivity. We investigated the cause of this sensitivity reduction.
Methods: Contrast sensitivity was measured for frequency doubling (0.25 cpd, 25 Hz) and nonflickering (4 cpd) gratings, arranged similarly to the targets in the FDT perimeter (Welch Allyn, Skaneateles Falls, NY, and Humphrey Instruments, San Leandro, CA). Various test orders were examined.
Results: Frequency-doubling (FD) sensitivity was reduced (0.15 log) in the second eye. A similar reduction occurred when first and second eye gratings were oriented orthogonally, suggesting that dichoptic contrast adaptation was not the cause. FD sensitivity was little affected after testing with nonflickering gratings, suggesting that fatigue effects were small. Sensitivity was reduced when testing was performed after 5 min of opaque occlusion. The use of a translucent occluder eliminated the reduction in sensitivity in the second eye.
Conclusion: We confirm the presence of reduced sensitivity in the second eye tested with FD perimetry and find that it is caused by delayed light adaptation post-occlusion.