Optophysiology of the Human RetinaWith Functional Ultrahigh Resolution Optical Coherence Tomography

Abstract

Purpose: : To introduce a possible optical analogue to electrophysiology for non–invasive depth resolved optical mapping of retinal response in the living human retina.

Methods: : Time and frequency domain optical coherence tomography (OCT) technology using light centered at 1040 nm has been developed for high speed (up to 15000 A–scans per second) ultrahigh resolution retinal imaging. Utilizing a light source emitting spectrum centred at 1040 nm compared to longer wavelength has the advantages to significantly reduce power losses due to water absorption and furthermore avoids pre–stimulation of the retina due to the laser spectrum positioned far away from the spectral sensitivity range of the photoreceptors. High speed OCT technology enables not only three–dimensional imaging but also high time resolution of up to 50 µs for detection of fast physiological changes.

Results: : OCT technology using 1040 nm light and simultaneous ERG measurements have been used to perform preliminary in vivo optophysiology measurements in normal human subjects. Measurements were performed over 8 seconds with 3 seconds pre–stimulus period and different light stimuli (7 ms to 200 ms, at multiple intensities and wavelengths below 850 nm) foveal and parafoveal. Dark scans of the same duration with no light stimulation were also acquired for baseline measurements. Subjects were cyclopleged and dark adapted or light adapted respectively before the measurements. Pronounced changes in the retinal backscattering specifically in the depth of the photoreceptor layer were observed in the single flash M–scans as compared to the dark scan M–scans. Limitations and challenges of this technique due to eye motions for in vivo optophysiology will be discussed.

Conclusions: : Non–contact, optical probing of retinal response to visual stimulation with ∼5 µm axial and ∼20 µm transversal resolution, by functional ultrahigh resolution optical coherence tomography was demonstrated for the first time in vivo in normal healthy subjects and could be correlated to simultaneous ERG measurements.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina • electroretinography: non-clinical