Analysis of the electroretinogram in toxoplasma retinochorioiditis.

The decision to use therapy in toxoplasma retinochorioiditis depends on the location of the active lesion and the presence of vitreous activity. In eyes with dense vitreous clouding it can be difficult to see whether the macular region is involved or not. In theory the localisation of a lesion can be estimated on the basis of the flash ERG. The standard flash electroretinogram was recorded in 23 patients with inactive toxoplasma retinochorioiditis lesions in the retina. In 17 cases a lesion was present within the central 12 degrees of the visual field, 8 of these had a reduced photopic ERG. In 15 patients lesions were found outside the central 12 degrees, in 8 of whom the scotopic ERG was reduced. We conclude that the ERG can be of use in indicating the scar location in patients with dense vitreous clouding.

The electrooculogram: a refinement of the method.

The measurement of the light rise of the corneoretinal potential in the clinical routine depends critically on the constancy of the eye movements made by the subject. To verify to what extent the variability of the Arden ratio can be explained by the variability of these eye movements, an infrared scleral reflection technique was applied in order to monitor eye position and electrooculogram simultaneously. The data obtained in 10 normal subjects show that not only is the variability reduced substantially by correction for the actual eye movement, but also the routine procedure gives a systematic underestimation of the ratio. Monitoring eye movements makes available the use of eye movements of arbitrary size (e.g., optokinetic nystagmus), allowing for application of the method in uncooperative subjects such as children.

Pattern ERG and glaucomatous visual field defects.

In the past five years numerous reports have suggested that ganglion cell function can be tested by means of a specialized form of electroretinography, the so-called pattern electroretinogram (PERG). Because of the important potentials of a ganglion cell test for clinical use this technique has been applied by several investigators to patients with (presumed) ganglion cell dysfunction, especially glaucoma. On grounds of principle we had reason to question whether the reported positive results should be attributed to ganglion cell dysfunction or to other factors such as optical disturbances. We investigated in this study the PERG as a function of visual field loss in glaucoma patients with careful control of optical factors. We did not find changes in PERG as a function of field loss. So either field loss is not related to the mass behaviour of ganglion cells, or ganglion cells are not the prime basis of the PERG. We believe the latter to be true.

The luminance origin of the pattern electroretinogram in man.

Electroretinograms (e.r.g.s) and visually evoked potentials (v.e.p.s) to pattern stimuli were recorded simultaneously from healthy subjects. The stimuli were produced by a configuration in which the luminance of two sets of spatial elements (checks) could be modulated independently. Experiments were designed to distinguish between contrast responses and non-linear luminance responses. In the first of two basic experiments, the luminance of only one set of checks was modulated, at a constant level in every trial. The other set was not modulated, but its luminance was set at various levels. Under these conditions the local luminance stimulation was kept equal for every trial whereas the contrast stimulation varied. Therefore, local luminance responses in these experiments were expected to be constant and contrast responses were expected to vary. The e.r.g.s were identical for all luminance settings of the unmodulated checks, suggesting that luminance rather than contrast determines the response. The v.e.p.s showed, on the contrary, the behaviour expected for contrast responses. In the second basic experiment the local luminance stimulation was also kept constant, but the phase difference between the modulations of the two sets of checks was varied between 0 deg (pure luminance stimulation) and 180 deg (pattern reversal). In this type of experiment the second harmonic responses to local luminance modulation are expected to decrease to a minimum as phase difference goes from 0 to 90 deg and increase again as phase difference goes to 180 deg. Contrast responses are expected to increase monotonically from zero to maximal at phase difference shifts from 0 deg (no contrast stimulation) to 180 deg (contrast reversal). The e.r.g.s decreased to a minimum at 90 deg phase difference and increase again with phase difference going to 180 deg. At 0 and 180 deg the same value was recorded. Consequently, the e.r.g. behaviour suggests a luminance origin of the responses. The v.e.p.s monotonically increased as phase difference went from 0 to 180 deg, thus suggesting a contrast origin of the responses. Two additional control experiments were performed. The first experiment compared the responses to homogeneous field red/green exchange and pattern red/green exchange, with the luminances of the red and green sources matched by heterochromatic flicker photometry. The exchange of luminance-matched red and green checks (pattern reversal) did not produce different e.r.g. responses from those recorded in response to homogeneous field red/green exchange. The v.e.p. showed a significant increase for the pattern stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)