Simultaneous recording of electroretinogram and visual evoked response. Focal stimulation under direct observation
T. Hirose, Y. Miyake and A. Hara
A system has been tested that allows simultaneous recording of the retinal
response (electroretinogram [ERG]) and the occipital response (visual
evoked response [VER]) with focal photic stimulation of the retina under
direct observation of the fundus. A helium-neon gas laser is used as a
stimulus source. The laser is chopped either by a pen motor or a rotating
disc. The laser is attached to a biomicroscope through which the examiner
can observe the fundus of the subject during the entire recording session.
The optically clear contact lens is made with a flat surface that
neutralizes refraction due to the cornea, thereby allowing fundus
observation by microscope. Two metal wires mounted inside and outside of
the lens serve as the electrode for the ERG. Graticules consisting of
concentric circles and radial lines are projected onto the subject's
fundus, providing a pattern that the examiner can use to determine the
exact location to be stimulated in the fundus. With proper adjustment of
stimulus and background illumination, local ERG and VER can be recorded
simultaneously by stimulating the macula.
