The contrast transfer function (CTF) of the pattern electroretinogram (PERG) depends on temporal frequency. For transient stimulation it is fully linear; at faster stimulation rates it becomes strongly non-linear with an accelerated shape. In this study we investigated a range of stimulus parameters with the aim of studying the influence of temporal and spatial frequencies, as well as contrast levels, on the CTF; effects were quantified via an "index of linearity" IL. Both reversal rate and check size influenced linearity (p < .001), examples: At a constant check size of 0.8°, 7.7 rps: IL = 1.0; 0.8°/24 rps: IL = 0.5; at a constant reversal rate of 19 rps, IL was 0.5 for 0.8°, but rose to 0.8 both for 0.2° and 18°. The reason for this complex response surface remains a puzzle, it cannot be explained by varying parvo/magnocellular contributions, and its possible influences on recordings in patients merit further studies.
Bibliographical noteFunding Information:
This study was made possible by a travel grant from the German Academic Exchange Service (DAAD), and support from the Joseph Alexander Foundation and the Alberto Moscona Foundation.
- Check size
- Contrast transfer characteristic
- Pattern ERG
- Temporal frequency