Non-invasive Optoretinography (ORG)

For many years visual inspection of fundus photography and examination of images acquired with optical coherence tomography (OCT) have been used by ophthalmologists for eye disease diagnosis and monitoring therapy progress thanks to their ability to detect morphological biomarkers of pathophysiology. However, early retinal degeneration might affect photoreceptor physiology and their functional response to light stimuli long before disrupting retinal morphology at a scale visible by clinical instruments. The anomalies in physiological response can be measured with Electroretinography (ERG), by recording the electrical currents generated directly by retinal neurons in combination with contributions from retinal glia. The drawback of ERG is that it measures an average response from large portions of the retina, and it might miss physiological changes occurring only in small areas. This issue can be partially solved by multifocal ERG, which measures the response from specific retinal regions. However, discriminating photoreceptor degeneration from that of the neural retina remains a problem.

More recently, a new technique called optoretinography (ORG) has been developed. In this technique, the physiological response to a single pulse light stimulus is measured with the use of OCT. In our work, we focus on the development of ORG that can measure response to a flicker stimulus. Similar measurements have been performed with ERG multiple times, and they have proven instrumental in the analysis of retinal light adaptation and critical flicker frequency (CFF) variations between the macula and periphery.

Our results have already demonstrated that we could detect the photoreceptor response to different flicker frequencies in a repeatable fashion. We also demonstrated the ability to spatially detect the response to a patterned stimulus with light stripes flickering at different frequencies. These results highlight the prospect for a more objective study of CFF variations across the retina or complete characterization of the spatially resolved temporal frequency response of the retina with flicker ORG perimetry and other novel accurate retinal functional studies for early detection of retinal degeneration and therapy monitoring.

Text: Sławomir Tomczewski, PhD, e-mail: stomczewski@ichf.edu.pl