Document Detail


Empiric limits of rod photocurrent component underlying a-wave response in the electroretinogram.
MedLine Citation:
PMID:  1633745     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The corneally recorded rod photocurrent component (photoresponse) underlying the a-wave feature of the electroretinogram was analyzed. The results set empiric limits on critical photoresponse variables. Measurements were obtained from four normal adult subjects on a-wave amplitude, a-wave velocity, b-wave amplitude, b-wave implicit time and b-wave height above baseline. At high intensity, interference from the b-wave component was minimized and the amplitude of the saturated photoresponse component was approximated by the a-wave feature. At lower intensities, the a-wave feature represented progressively less of the underlying photoresponse amplitude. Photoresponse amplitude saturation was signaled by the abrupt slowing of the rate of decline of b-wave peak latency and occurred at an intensity about 2.5 log units above the first appearance of the b-wave. At the intensity of photoresponse saturation, the peak amplitude of the a-wave feature was only about 25% of the maximum amplitude of the underlying photoresponse component. A-wave leading edge velocity was found to increase up to 3 log units above the intensity of photoresponse amplitude saturation and to provide a good estimate of photoresponse velocity at higher intensities. A cascaded low-pass filter model with modifications to accommodate amplitude and timing nonlinearities was used to generate a set of probable underlying photoresponses from the analysis of a-wave amplitude and velocity. Movement of the a-wave leading edge to the left at higher intensities in algebraic combination with a static b-wave leading edge above the intensity of photoresponse amplitude saturation was found to explain the second rise of the b-wave amplitude function and the decline of b-wave amplitude above baseline at high intensities. This analysis provides a basis for modeling the underlying photoresponse on a biochemical level and for interpreting photoreceptor damage in disease states.
Authors:
M E Breton; D P Montzka
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Documenta ophthalmologica. Advances in ophthalmology     Volume:  79     ISSN:  0012-4486     ISO Abbreviation:  Doc Ophthalmol     Publication Date:  1992  
Date Detail:
Created Date:  1992-08-26     Completed Date:  1992-08-26     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0370667     Medline TA:  Doc Ophthalmol     Country:  NETHERLANDS    
Other Details:
Languages:  eng     Pagination:  337-61     Citation Subset:  IM    
Affiliation:
Scheie Eye Institute, Department of Ophthalmology, University of Pennsylvania School of Medicine, Philadelphia 19104.
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MeSH Terms
Descriptor/Qualifier:
Adolescent
Adult
Electroretinography*
Female
Humans
Male
Membrane Potentials / physiology
Middle Aged
Photic Stimulation
Photoreceptor Cells / physiology*,  physiopathology
Retinal Degeneration / physiopathology
Sensory Thresholds

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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