Purchase this article with an account.
M.K. Menz, M.D. Menz, E.E. Sutter; Fast Adaptive Mechanisms of Rod Responses Revealed With the Multifocal ERG . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1652.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To study the local, fast adapting responses of rods in the normal human retina occurring over a time interval of tens of milliseconds.
Multifocal electroretinograms (mfERG) were recorded from two normal subjects. Stimulation and analysis were performed with the VERIS 5 Science system. A special stimulation mode (time–slice recording introduced at ARVO 2004, poster #4228) was used that permits probing the multifocal responses at brief intervals (4 probe flashes, delivered every other frame [75Hz frame rate]) after periodic intervals of dark adaptation (9 frames). The special analysis permitted separate processing of the responses to each of the probes between the periodic dark intervals. The derivation of each such time slice was based on a complete m–sequence cycle. The probe flashes were photopically matched blue/red (blue was 0.7 and red –0.6 log scot td–s) using a color CRT, so that cone responses were suppressed. The stimulus display consisted of 61 equal–sized hexagons, with a blue background of intensity 3.5 log scot td. The right eye was dark–adapted for twenty minutes prior to recording in a darkened room. Recording sessions lasted 15 minutes and were repeated three times for each subject. The three data sets from both subjects were combined for analysis.
The scalar product topography (no spatial averaging, baseline on, 0–150 ms) for the first probe after 9 dark frames reflects rod distribution, with a depression in the center and a ring of elevated activity between 10–15 degrees eccentricity. There was also a good depression at the disk. With the succeeding probes the overall response was reduced but the topography remained similar. Ring averages exhibited different dynamics at different eccentricities. Ring 2 (3–7 degrees eccentricity) displayed a pure amplitude decrease with successive probes. Rings 3 and 4 (7–16 degrees eccentricity) show a decrease in amplitude and increase in latency (from 50 to 60 ms) of P1. Ring 5 (16–21 degrees eccentricity) exhibits little amplitude change but it also has an increase in latency (from 50 to 60 ms) of P1. There were also differences by quadrants. The nasal field scalar product was reduced between the first and second probe flashes, but not for the temporal field.
We obtained retinal topographies with rod–like distributions. Since complete silencing of all three cone populations is not possible, a small contribution from s–cones may be present. The adaptation of rod responses as a function of time after darkness (from 0–80 ms) showed local differences, both with eccentricity and by quadrants.
This PDF is available to Subscribers Only