Contribution of isolated cone driven responses to the topography of the multifocal oscillatory potentials (mfOPs)

Abstract

Abstract: : Purpose: The aim of this study was to obtain topographical information about inner retinal function defined by the black–white and single cone class driven multifocal oscillatory potentials of the human retina. Methods: We examined inner retinal function in protanopes, deuteranopes and normal trichromats using multifocal oscillatory potentials (mfOPs). They were recorded using the standard (black–white) stimulus as well as using stimuli aimed to isolate a single photoreceptor class. The stimulus was generated on a flat–screen SONY Trinitron monitor with a resolution of 1024 x 768 pixels. It consisted of 61 hexagonal elements which subtended 84° x 75° of visual angle at a viewing distance of 18 cm. To isolate the long wavelength (L) and middle wavelength (M) sensitive cones stimulus colors were calculated on the basis of the Stockman & Sharpe cone fundamentals. The maximum contrast for both cone isolating conditions was 47% with a mean luminance of 19.2 cd/m2 for L– and 33.8 cd/m2 M–cones. The recordings were obtained with the VERIS (3.0.1) system using DTL fiber electrodes. Results: The results show that our dichromats with a single gene (either a single M–pigment gene in protanopes or a single L–M–hybrid pigment gene in deuteranopes) in their L/M–gene array give similar response waveform topographies to those of trichromats for the first (K1) and second order kernel (K2) of the mfOP. The response amplitudes for both kernels (K1 and K2) in trichromats vary with the relative number of L– and M–cones estimated from cone isolated mfERG recordings. However, in mfOPs (K1 and K2) protanopes show similar waveform but higher response amplitudes than deuteranopes. Conclusions: The first order kernel (K1) of the mfOP is possibly dominated by cone responses while K2 may be dominated by rod responses (Wu & Sutter, 1995). Our data suggest that cone driven signals are present in both K1 and K2. Differences found between black–white and isolated cone class driven response waveforms may identify direct contribution of rods to the response waveforms.

Keywords: electroretinography: non–clinical • color vision • photoreceptors