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...

Novel ultra-broad bandwidth light sources enabling unprecedented sub-2 microm axial resolution over the 400 nm-1700 nm wavelength range have been developed and evaluated with respect to their feasibility for clinical ultrahigh resolution optical coherence tomography (UHR OCT) applications. The state-of-the-art light sources described here include a compact Kerr lens mode locked Ti:sapphire laser (lambdaC = 785 nm, delta lambda = 260 nm, P(out) = 50 mW) and different nonlinear fibre-based light sources with spectral bandwidths (at full width at half maximum) up to 350 nm at lambdaC = 1130 nm and 470 nm at lambdaC = 1375 nm. In vitro UHR OCT imaging is demonstrated at multiple wavelengths in human cancer cells, animal ganglion cells as well as in neuropathologic and ophthalmic biopsies in order to compare and optimize UHR OCT image contrast, resolution and penetration depth.

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Impaired ocular blood flow is involved in the pathogenesis of numerous ocular diseases like glaucoma or AMD. The purpose of the present study was to introduce and validate a novel, microscope based, non invasive laser Doppler flowmeter (NILDF) for measurement of blood flow in the choroid. The custom made NI-LDF was compared with a commercial fiber optic based laser Doppler flowmeter (Perimed PF4000). Linearity and stability of the NI-LDF were assessed in a silastic tubing model (i.d. 0.3 mm) at different flow rates (range 0.4 – 3 ml/h). In a rabbit model continuous choroidal blood flow measurements were performed with both instruments simultaneously. During blood flow measurements ocular perfusion pressure was changed by manipulations of intraocular pressure via intravitreal saline infusions. The NILDF measurement correlated linearly to intraluminal flow rates in the perfused tubing model (r = 0.99, p<0.05) and remained stable during a 1 hour measurement at a constant flow rate. Rabbit choroidal blood flow measured by the PF4000 and the NI-LDF linearly correlated with each other over the entire measurement range (r = 0.99, y = x* 1,01 – 12,35 P.U., p < 0,001). In conclusion, the NI-LDF provides valid, semi quantitative measurements of capillary blood flow in comparison to an established LDF instrument and is suitable for measurements at the posterior pole of the eye.

These projections provide an objective basis to estimate the resources that may be needed by health authorities and care providers such as ophthalmologists in the future and should help to design glaucoma blindness prevention programs or screening studies in Austria. The predicted continuous increase of Europe's older population will prove to become a challenge for public health professionals not only for diagnosis and monitoring, but also for the treatment of glaucoma.