The slow light and dark oscillation of the clinical electro-oculogram

Retinal electrophysiology in central nervous system disorders. A review of human and mouse studies

The retina and brain share similar neurochemistry and neurodevelopmental origins, with the retina, often viewed as a "window to the brain." With retinal measures of structure and function becoming easier to obtain in clinical populations there is a growing interest in using retinal findings as potential biomarkers for disorders affecting the central nervous system. Functional retinal biomarkers, such as the electroretinogram, show promise in neurological disorders, despite having limitations imposed by the existence of overlapping genetic markers, clinical traits or the effects of medications that may reduce their specificity in some conditions. This narrative review summarizes the principal functional retinal findings in central nervous system disorders and related mouse models and provides a background to the main excitatory and inhibitory retinal neurotransmitters that have been implicated to explain the visual electrophysiological findings. These changes in retinal neurochemistry may contribute to our understanding of these conditions based on the findings of retinal electrophysiological tests such as the flash, pattern, multifocal electroretinograms, and electro-oculogram. It is likely that future applications of signal analysis and machine learning algorithms will offer new insights into the pathophysiology, classification, and progression of these clinical disorders including autism, attention deficit/hyperactivity disorder, bipolar disorder, schizophrenia, depression, Parkinson's, and Alzheimer's disease. New clinical applications of visual electrophysiology to this field may lead to earlier, more accurate diagnoses and better targeted therapeutic interventions benefiting individual patients and clinicians managing these individuals and their families.

Is white the right light for the clinical electrooculogram?

PURPOSE

To investigate if a lower luminance monochromatic LED stimulus could be used as an alternative to a high luminance white light for the clinical electrooculogram.

METHODS

Clinical electrooculograms were recorded in color normal participants (N = 23) aged 22.6 ± 1.2 years, 7 male and 16 female using the standard 100 cd.m^-2 white illuminant and four monochromatic LEDs with peak wavelengths of 448, 534, 596 and 634 nm at 30 cd.m^-2. Pupils were dilated and there was a 30 cd.m^-2pre-adaptation to white light for 2 min followed by 15 min dark adaptation and 20 min recording in the light stimulus using a Ganzfeld stimulator.

RESULTS

The normalized LP:DTratio for the short wavelength LED (448 nm) was equivalent in amplitude and timing to the ISCEV standard EOG (p = .99). The LP:DTratio for the white (100 cd.m^-2) and 448 nm (30 cd.m^-2) were (median ± SEM): 2.49 ± .11 and 2.47 ± .11. The time to light-rise peak was also equivalent being 9.0 ± .2 and 8.0 ± .4 min (p = .54).

CONCLUSIONS

Consideration may be given to using a short wavelength monochromatic stimulus that is more comfortable for the subject than the current 100 cd.m^-2 illuminant.

Electro-oculography in bilateral optic neuropathy

Objective

Effect of bilateral, optic neuropathy on the function of retinal pigment epithelium has not been investigated extensively to date. This study aimed to determine the effect of bilateral, optic neuropathy on light peak:dark trough ratio, light peak and dark trough values of electro-oculography. Thirty-seven patients with a clinical diagnosis of bilateral optic neuropathy and 40 control subjects were recruited in this observational, cross-sectional study, carried out at the Neurophysiology unit, Teaching Hospital, Peradeniya, Sri Lanka. Pattern reversal visual evoked potentials, pattern electroretinography and electro-oculography were recorded in all of them.

Results

Twenty-four patients (64.9%) had reduced light peak:dark trough ratio values. The median light peak:dark trough ratio ± inter quartile range of the patient group (1.50 ± 0.4) was significantly lower than that of the controls (1.80 ± 0.2), (p < 0.001). Median dark trough value was significantly higher in patients compared to the control value. These changes may be due to higher conductance of ion channels in the retinal pigment epithelium, sub retinal space creation, changes in choroidal circulation or secondary to photoreceptor abnormalities in the macular region. These results indicate that retinal pigment epithelium might be affected in bilateral optic neuropathy.