Studying the biology of brain in action is key to understand psychiatric disorders. However, limited options and techniques exist to do this. One emerging technique is measuring the retinal activity.Retinal activity may reflect the central neurochemistry underlying brain disorders and could represent a means to differentiate brain pathologies. ERG, flash electro retinogram, is used to record the light-evoked electric potential originating from the retina in response to a light stimulus.
Lavoie J, Maziade M and Hébert M review the findings of ERG in this article.
ERG: On a typical flash ERG trace, two major components can be observed: Initial negative wave, called the a-wave representing the hyperpolarization of the photoreceptors for the most part. This is followed by a positive wave, namely the b-wave generated mainly by bipolar cells. Electrode is placed on the surface of the eye and reference and ground electrodes are placed on the skin of the subject, usually the outer canthus and forehead respectively and a light source is used to stimulate the receptors.
Seasonal Affective Disorder: Two specific retinal anomalies are observed. Decreased rod sensitivity and diminished cone Vmax. (Vmax= the amplitude where the system saturates on the luminance- response function curve generated by plotting wave amplitudes against the flash luminance). These may represent state markers of the disease ( i.e. present only in depression state & cab be modified by appropriate treatment)
Schizophrenia: Diminished cone a-wave amplitude , signalling a photoreceptor deficit, suggest impairments in the earliest stage of the visual information processing in shizophrenia. ERG anomalies are reported in high risk children also . There are only few studies with small numbers and results are inconsistent.
Autism: Reduced rod b wave amplitude reported in patients and relatives in studies with very small numbers.
It is too early to comment on the usefulness of ERG in psychiatric disorders. It needs to be seen how much specific these reported changes are in larger samples.Current research is troubled by small numbers, non replicated findings and differing protocols. The idea of looking in to the mind through the eyes is inspiring, and hopefully, ERG might throw more light on neurodeveleopmental/ neurophysiological basis of mental phenomena and disorders.
Summary of the article:
Lavoie J, Maziade M, Hébert M.Prog Neuropsychopharmacol Biol Psychiatry. 2014 Jan 3;48:129-34.