Effect of Area and Intensity on the Size and Shape of the Electroretinogram : Exclusion of Stray Light Effects

Abstract

SINCE Adrian and Matthews (1928) showed that the latent period of the optic nerve discharge can be influenced by the size of the area stimulated, the effect of area on the electroretinogram has been confirmed by a number of workers (Granit, 1933;Creed and Granit, 1933;Fry and Bartley, 1935;Boynton and Riggs, 1951).The size and shape of the electroretinogram can be influenced in the same way by increasing the stimulated area as by increasing the intensity ofthe stimulus. Fry and Bartley (1935) stated that the effect of areawas due almost entirely to stray light; they believed the effect of the focal area to be small. They performed the following experiment on the intact rabbit eye:Two adjacent bright areas were exposed alternately against a dark background. Since the amount of stray light was the same in each case and diffusely distributed over the retina, alteration could not affect it: each of the two retinal spots, however, should respond intermittently if the focal response were dominant. Actually, at fast rates of alternation, no response was obtained, and this finding was explained on the assumption that stray light, being constant and independent of the area stimulated, acted as a much more effective constant background than the alternating focal points, which were therefore believed to elicit only a negligible fraction of the b-wave. Granit, Rubinstein, and Therman (1935) disagreed with this generalization. To test it they produced,< on the retina of the excised and opened frog eye, two sharply focused spots, about 0 4 mm. in diameter and 0 3 mm. apart.Threshold stimuli were used to elicit a response of about 50 ,uV. In this case the two stimuli A and B together elicited a response only 10-15 per cent. less than the expected value of A+B. Stray light could thus account for only this percentage of the combined response. Nevertheless when one flash was made to succeed the other, the effect of the second was inhibited. They concluded that adjacent neurones also were influenced by some kind of physiological spread of the electrical response, while admitting of course the existence of stray light unless special precautions were taken to avoid it.More recently Boynton and liggs (1951) and Asher (1951) have emphasized that the retinal response is primarily aroused by stray light rather than

Spatial characteristics of the oscillatory potentials of the electroretinogram

“…2A). The results are in good accord with the literature in that responses from different retinal areas have been shown to be additative (Wirth & Zetterstrom 1954;Brindley 1956;Crampton 1957;Brindley & Westheimer 1965;Armington 1968). To further minimize the stray light problem, recordings were also made intra-retinally with a microelectrode in order to eliminate the gross ERG elicited by stray light.…”

Further Study on the Intraretinal Action Potentials and on the Site of Erg Generation

“…Nevertheless, the independence of the focal potentials from the ERG processes is still maintained for the following reasons: 1) They are highly localized within and in close proximity to the illuminated area ( fig.3), whereas the ERG appears, apart from the problem of scattered light, to be a more diffuse potential (4,5,16,25). 2) The focal potentials are more susceptible to aging and chemical agents than the ERG.…”

Analysis of the electroretinogram in toxoplasma retinochorioiditis

“…the whole retina. Many authors have studied the possibility of stimulation of a localised area [22][23][24][25][26][27][28] with variable success. Obviously, localised stimulation is not possible in patients with dense vitreous clouding.…”

“…Results from some of the studies on localised stimulation indicate that a considerable part of the photopic Ganzfeld response is determined by the central part of the retina [22,23,28]. In fact authors state that 'the change of response amplitude with eccentricity was probably too large to be attributed to the count of the number of cones combined with the Stiles Crawford effect' [23].…”