Faculty Collaboration Database

Estimates of L:M cone ratio from ERG flicker photometry and genetics. J Vis 2002;2(8):531-42

Date

04/08/2003

Pubmed ID

12678637

DOI

10.1167/2.8.1

Scopus ID

2-s2.0-0038181021 (requires institutional sign-in at Scopus site)   137 Citations

Abstract

Estimates of L:M cone ratio for males with normal color vision were derived using the flicker-photometric electroretinogram (ERG). These were obtained by best fitting ERG spectral sensitivity functions to a weighted sum of long (L)- and middle (M)-wavelength-sensitive cone spectral absorption curves. Using the ERG, measurements can be made with extremely high precision, which leaves variation in the wavelength of maximal sensitivity (lambda(max)) of the cone photopigments as the major remaining source of inaccuracy in determining the ratio of cone contributions. Here that source of inaccuracy was largely eliminated through the use of individualized L-cone spectral absorption curves deduced from L-pigment gene sequences. The method was used on 62 normal males as part of an effort to obtain a true picture of how normal variations in L:M cone ratio are distributed. The percentage of L cones in the average eye was 65%L [where %L = 100 X L / (L+M)]. There were huge individual differences ranging from 28%-93%L, corresponding to more than a 30-fold range in L:M ratio (0.4-13). However, the most extreme values were relatively rare; 80% of the subjects fell within +/-15 %L of the mean, corresponding to a 4-fold range in L:M ratio (1-4). The method remedies major weaknesses inherent in earlier applications of flicker photometry to estimate cone ratio; however, it continues to depend on the assumption that the average L cone produces a response with an identical amplitude to that of the average M cone. A comparison of the ERG results with the distribution of cone ratios estimated from cone pigment messenger RNA in cadaver eyes indicates that the assumption generally holds true. However, there may be a small number of exceptions in which individuals have normally occurring (but relatively rare) amino acid substitutions in one of their pigments that significantly affect the physiology of the cone class containing that pigment, so as to reduce the amplitude of its contribution to the ERG. Consistent with this possibility, extreme cone contribution ratios were found to be associated with atypical L-pigment amino acid combinations.

Author List

Carroll J, Neitz J, Neitz M

Author

Joseph J. Carroll PhD Director, Professor in the Ophthalmology and Visual Sciences department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Adolescent
Adult
Child
Color Perception
Color Vision Defects
Electroretinography
Genetic Variation
Humans
Male
Middle Aged
Photometry
Polymerase Chain Reaction
RNA, Messenger
Retinal Cone Photoreceptor Cells
Rod Opsins