Optophysiology: Depth-resolved probing of retinal physiology with functional ultrahigh-resolution optical coherence tomography

Abstract

Noncontact, depth-resolved, optical probing of retinal response to visual stimulation with a <10-m spatial resolution, achieved by using functional ultrahigh-resolution optical coherence tomography (fUHROCT), is demonstrated in isolated rabbit retinas. The method takes advantage of the fact that physiological changes in dark-adapted retinas caused by light stimulation can result in local variation of the tissue reflectivity. fUHROCT scans were acquired from isolated retinas synchronously with electrical recordings before, during, and after light stimulation. Pronounced stimulusrelated changes in the retinal reflectivity profile were observed in the inner͞outer segments of the photoreceptor layer and the plexiform layers. Control experiments (e.g., dark adaptation vs. light stimulation), pharmacological inhibition of photoreceptor function, and synaptic transmission to the inner retina confirmed that the origin of the observed optical changes is the altered physiological state of the retina evoked by the light stimulus. We have demonstrated that fUHROCT allows for simultaneous, noninvasive probing of both retinal morphology and function, which could significantly improve the early diagnosis of various ophthalmic pathologies and could lead to better understanding of pathogenesis.electroretinogram ͉ functional optical coherence tomography ͉ inner plexiform layer ͉ photoreceptors ͉ retinal imaging T he vertebrate retina consists of several distinct layers: nuclear layers containing cell bodies can be differentiated from plexiform layers with axons and dendrites forming the neuronal network that preprocesses light-evoked signals before transmission to the brain. Early stages of retinal disorders are often confined to one of these layers and are manifested by both morphological abnormalities and impaired physiological responses. Detection of such pathologies requires high-resolution imaging methods. Various imaging modalities such as fundus photography, ultrasound imaging, and optical coherence tomography (OCT) are clinically used for imaging retinal morphology. OCT is an emerging imaging technique that allows for noncontact, in vivo visualization of biological tissue morphology with a micrometer-scale resolution at imaging depths of 1-2 mm (1-3). Currently, electrophysiological tests such as electroretinography (ERG) (4) and multifocal ERG (5) are used for clinical assessment of retinal function.More then 25 years ago, it was observed that the isolated retina when stimulated with visible light changes the amount of transmitted near-infrared light (NIR) (6, 7). Photoreceptors (PRs) were determined to be the main source of this effect, and in the following years, this method was used for investigation and quantitative evaluation of the activation of the PR G protein transducin and the time course of transduction events (8-10 and reviewed in ref. 11). In the last few years, other physiological processes at the cellular and subcellular level such as membrane depolarization (12), cell swelling (13), and altered metabolism...

A Review of Algorithms for Segmentation of Retinal Image Data Using Optical Coherence Tomography

“…Moreover, measuring the reflectance of the various retinal layers on OCT images may also be of interest. Drexler et al have shown in in vitro and in vivo (Bizheva et al, 2006;Hermann et al, 2006) studies that physiological processes of the retina lead to optical density changes that can be observed by a special M-mode OCT imaging, known as optophysiology. Thus, it also seems rational that quantitative analysis of reflectance changes may provide clinically relevant information in retinal patophysiology.…”

Optical coherence tomography—current technology and applications in clinical and biomedical research

“…It is also the key to imaging large comprehensive 3 D volumes [173] or to the time-resolved observation of dynamic processes [44,45,167]. The recent commercialization of high speed line cameras and swept sources will therefore be an important factor driving the development of the next generation of OCT systems.…”

“…Compared to other techniques like electro-retinography, OCT provides uncomplicated, non-invasive access for studying the retinal physiology, and may open new possibilities to investigate retinal pathologies [44,167].…”

“…SD-OCT, or the sweep rate of the light source in SS-OCT. Fast image acquisition is important for sampling large volumes-especially for in vivo imaging where sample motion cannot be avoided [43]-and it opens the possibility to observe dynamic phenomena temporally resolved [44,45]. Typical state-of-the-art research systems feature A-scan rates up to several hundreds of kilohertz.…”

Decreased photoreceptor inner segment/outer segment junction reflectivity in patients with idiopathic epimacular membrane

“…In a healthy macula, IS/OS junction can be seen as a continuous hyper-reflective band on OCT image, and recent studies demonstrated that decreased reflectivity of this layer is associated with diminished photoreceptor function. 18,19 Based on this knowledge, loss of reflectivity in IS/OS junction and ELM might indicate that EMM leads to subclinical functional or structural impairment in these layers. However, correlation analysis did not show a significant association between reflectivity values and CDVA.…”