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Optical microsurgery confined to the retinal pigment epithelium (RPE) requires locally optimized laser parameters and reliable real-time feedback dosimetry (RFD) to prevent unwanted neuroretinal overexposure. This study aimed to compare pulses of different durations and application modes (single, ramp, burst). Moreover, optical coherence tomography (OCT)-based RFD was investigated in an ex vivo experiment, utilizing nine porcine eyes that were exposed to laser pulses of 8, 12, 16 and 20 µs duration (wavelength: 532 nm, exposure area: 90 × 90 µm2, radiant exposure: 247 to 1975 mJ/µm2). Simultaneously, time-resolved OCT M-scans were recorded (central wavelength: 870 nm, scan rate: 85 kHz) for RFD. Post irradiation, retinal changes were assessed with color fundus photography (CFP) and cross-sectional OCT B-scans. RPE cell damage was quantified via fluorescence-based cell viability assay and compared to the OCT dosimetry feedback. Our experiments indicate cumulative RPE damage for pulse bursts of 16 µs and 20 µs, whereas no cumulative effects were found for pulse durations of 8 µs and 12 µs applied in ramp mode. According to statistical analysis, OCT-RFD correctly detected RPE cell damage with 96% sensitivity and 97% specificity using pulses of 8 µs duration in ramp mode.

Selective retina therapy (SRT) is a short pulse (μs-regime) alternative to conventional laser photocoagulation (LPC) for treatment of retinal diseases. LPC leads to collateral damage of retinal layers adjacent to the retinal pigment epithelium (RPE), including healthy, non-regenerative photoreceptors due to the high thermal load, whereas in SRT, RPE cells are destroyed by microbubbles without damaging the neuronal retina. A novel experimental SRT laser operating at 532 nm wavelength can deliver 2 – 20 μs pulse sequences. Its tight integration into an upgraded diagnostic SPECTRALIS system combines beam control for treatment planning with real-time optical coherence tomography (OCT) overexposure protection of the photoreceptors. This “Spectralis Centaurus” system, was built and preliminary tested on porcine ex-vivo samples, reaching an unprecedented accuracy with unique planning and follow-up capabilities for upcoming clinical cellular level micro-surgery. The combination of OCT with SRT selectively limits cell death to the RPE by precisely controlling energy deposition while optically monitoring tissue response.

Laser photocoagulation of the retina has been performed for more than 40 years and has enabled the denaturation of retinal layers by the deposition of heat in tissue. However, for treatment of pathologies associated retinal pigment epithelium (RPE), excessive damage of adjacent tissue, especially the damage of the photoreceptor layer is considered to be disproportionate.

Monitoring subtle choroidal thickness changes in the human eye delivers insight into the pathogenesis of various ocular diseases such as myopia and helps planning their treatment. However, a thorough evaluation of detection-performance is challenging as a ground truth for comparison is not available. Alternatively, an artificial ground truth can be generated by averaging the manual expert segmentations. This makes the ground truth very sensitive to ambiguities due to different interpretations by the experts. In order to circumvent this limitation, we present a novel validation approach that operates independently from a ground truth and is uniquely based on the common agreement between algorithm and experts. Utilizing an appropriate index, we compare the joint agreement of several raters with the algorithm and validate it against manual expert segmentation. To illustrate this, we conduct an observational study and evaluate the results obtained using our previously published registration-based method. In addition, we present an adapted state-of-the-art evaluation method, where a paired t-test is carried out after leaving out the results of one expert at the time. Automated and manual detection were performed on a dataset of 90 OCT 3D-volume stack pairs of healthy subjects between 8 and 18 years of age from Asian urban regions with a high prevalence of myopia.

Selective treatment of the retinal pigment epithelium (RPE) by using short-pulse lasers leads to a less destructive treatment for certain retinal diseases in contrast to conventional photocoagulation. The introduction of selective retina therapy (SRT) to clinical routine is still precluded by the challenges to reliably monitor treatment success and to automatically adjust dose within the locally varying therapeutic window. Combining micrometer-scale depth resolving capabilities of optical coherence tomography (OCT) with SRT can yield real-time information on the laser-induced changes within the RPE after a laser pulse or even during treatment with a laser pulse train. In the present study, SRT and OCT were combined to treat ex-vivo porcine eyes demonstrating closed-loop dose-control. We found a reliable correlation of specific signal changes in time resolved OCT images and physiological lesions in the RPE. First experiments, including 23 porcine eyes, prove the feasibility of the novel treatment concept.

Purpose Selective retina therapy (SRT) has shown great promise compared to conventional retinal laser photocoagulation as it avoids collateral damage and selectively targets the retinal pigment epithelium (RPE). Its use however is challenging in terms of therapy monitoring and dosage because an immediate tissue reaction is not biomicroscopically discernibel. To overcome these limitations real time optical coherence tomography (OCT) might be useful to monitor retinal tissue during laser application. We have thus evaluated a proprietary OCT system for its capability of mapping optical changes introduced by SRT in retinal tissue. Methods Freshly enucleated porcine eyes covered in DMEM upon collection were utilized and a total of 175 scans from ex vivo porcine eyes were analyzed. The porcine eyes were used as an ex vivo model and results compared to two time resolved OCT scans recorded from a patient undergoing SRT treatment (SRT Vario Medical Laser Center Lübeck). In addition to OCT fluorescin angiography and fundus photography were performed on the patient and OCT scans were subsequently investigated for optical tissue changes linked to laser application. Results Biomicroscopically invisible SRT lesions were detectable in OCT by changes in the RPE / Bruch's complex both in vivo and the porcine ex vivo model. Laser application produced clearly visible optical effects such as hyper reflectivity and tissue distortion in the treated retina. Tissue effects were even discernible in time resolved OCT imaging when no hyper reflectivity persisted after treatment. Data from ex vivo porcine eyes showed similar to identical optical changes while effects visible in OCT appeared to correlate with applied pulse energy leading to an additional reflective layer when lesions became visible in indirect ophthalmoscopy. Conclusions Our results support the hypothesis that real time high resolution OCT may be a promising modality to obtain additional information about the extent of tissue damage caused by SRT treatment. Data shows that our ex vivo porcine model adequately reproduces the effects occurring in vivo and thus can be used to further investigate this promising imaging technique.

Selective retina therapy and optical coherence tomography have been combined to monitor laser-tissue interaction in real-time. An ex-vivo study of porcine eyes unveils mechanisms that enable automated and accurate dose-control during laser-therapy.

Recognizing significant temporal changes in the thickness of the choroid and retina at an early stage is a crucial factor in the prevention and treatment of ocular diseases such as myopia or glaucoma. Such changes are expected to be among the first indicators of pathological manifestations and are commonly dealt using segmentation-based approaches. However, segmenting the choroid is challenging due to low contrast, loss of signal and presence of artifacts in optical coherence tomography (OCT) images. In this paper, we present a novel method for early detection of choroidal changes based on piecewise rigid image registration. In order to adhere to the eye’s natural shape, the regularization enforces the local homogeneity of the transformations in nasal-temporal (x-) and superior-inferior (y-) direction by penalizing their radial differences. We restrict our transformation model to anterior-posterior (z-) direction, as we focus on juvenile myopia, which correlates to thickness changes in the choroid rather than to structural alterations. First, the precision of the method was tested on an OCT scan-rescan data set of 62 healthy Asian children, ages 7 to 13, from a population with a high prevalence of myopia. Furthermore, the accuracy of the method in recognizing synthetically induced changes in the data set was evaluated. Finally, the results were compared to those of manually annotated scans.

Detecting and monitoring changes in the human choroid play a crucial role in treating ocular diseases such as myopia. However, reliable segmentation of optical coherence tomography (OCT) images at the choroid-sclera interface (CSI) is notoriously difficult due to poor contrast, signal loss and OCT artefacts. In this paper we present blockwise registration of successive scans to improve stability also during complete loss of the CSI-signal. First, we formulated the problem as minimization of a regularized energy functional. Then, we tested our automated method for piecewise Intensity-based Choroidal rigid Registration using regularized block matching (ICR) on 20 OCT 3D-volume scan-rescan data set pairs. Finally, we used these data set pairs to determine the precision of our method, while the accuracy was determined by comparing our results with those using manually annotated scans.

High-resolution frequency domain optical coherence tomography (OCT) stands out amongst a range of novel dermatologic imaging technologies, with its good detection sensitivity around -100 dB, high measurement speeds allowing real-time image acquisition and its ability to acquire high definition cross-sectional and 3D tomograms of regions greater than 1 cm2, providing tissue information comparable to conventional histopathology without the need for any contrast agents. Typical axial and transverse resolutions of state-of-the-art OCT systems range between 1–10 µm and approximately 20 µm, respectively, depending on the employed wavelength region. This review investigates the significant progress accomplished in the field of dermatologic OCT with respect to other in vivo diagnostic methods for pre-excisional imaging of nonmelanoma skin cancers and specifically emphasizes state-of-the-art results achieved in different clinical pilot studies. Further technological extensions of OCT, various multimodal imaging ap...

PURPOSE: To gather sub-surface in situ images of microneedle-treated human skin, in vivo, using optical coherence tomography (OCT). This is the first study to utilise OCT to investigate the architectural changes that are induced in skin following microneedle application. METHODS: Steel, silicon and polymer microneedle devices, with different microneedle arrangements and morphologies, were applied to two anatomical sites in human volunteers following appropriate ethical approval. A state-of-the-art ultrahigh resolution OCT imaging system operating at 800 nm wavelength and

The range of genetic and genomic resources available makes the mouse a powerful model for the genetic dissection of complex traits. Because accurate, high-throughput phenotypic characterisation is crucial to the success of such endeavours, we recently developed an optical coherence tomography (OCT) system with extended depth range scanning capability for measuring ocular component dimensions in mice. In order to test whether the accuracy and reproducibility of our OCT system was sufficient for gene mapping studies, we carried out an experiment designed to estimate the heritability of mouse ocular component dimensions. High-resolution, two dimensional tomograms were obtained for both eyes of 11 pairs of 8 week-old outbred MF1 mice. Subsequently, images were obtained when their offspring were aged 8 weeks. Biometric data were extracted after image segmentation, reconstruction of the geometric shape of each surface, and calculation of intraocular distances. The repeatability of measurements was evaluated for 12 mice scanned on consecutive days. Heritability estimates were calculated using variance components analysis. Sets of tomograms took ∼2 s to acquire. Biometric data could be obtained for 98% of the 130 eyes scanned. The 95% limits of repeatability ranged from ±6 to ±16 μm for the axial ocular component dimensions. The heritability of the axial ocular components was 0.6–0.8, except for corneal thickness, which had a heritability not significantly different from zero. In conclusion, axial ocular component dimensions are highly heritable in mice, as they are in humans. OCT with extended depth range scanning can be used to rapidly phenotype individual mice with sufficient accuracy and precision to permit gene mapping studies.

PURPOSE: To investigate and demonstrate early structural changes of the retina/pigmentepithelial/choriocapillaris (RPECC) complex before and 10 ± 3 days after intravitreal application of bevacizumab (Avastin®) in patients with neovascular age related macular degeneration (nAMD) by comparison of standard Stratus Optical Coherence Tomography (S-OCT) and Ultra High Resolution (UHR-OCT) imaging systems. METHODS: Six patients with nAMD were examined in a consecutive case series with UHR-OCT and Stratus OCT one day before and 10 ± 3 days after intravitreal application of 1.25 mg (0.125 ml) bevacizumab (Avastin®). Maximum central retinal thickness (CRT) was measured with the retinal thickness program and calliper measuring function of S-OCT and by the measuring tool of Adobe Photoshop 5.0 in UHR-OCT pictures. RESULTS: In three of six cases residual fluid after treatment was only visible with UHR-OCT but not with the S-OCT. A decrease of maximum CRT could be shown in all cases in UHR-OCT pictures but only in half of the cases (6/3) in S-OCT pictures. In 2/6 cases vitreoretinal adhesions were demonstrable with UHR-OCT but not seen with the S-OCT, irregularities in the photoreceptor layer could be revealed clearly by UHR-OCT in 2/6 cases. CONCLUSION: After anti-VEGF treatment, UHR–OCT gives more accurate information about residual fluid and intraretinal damage than S-OCT and offers more precise measurements of maximum CRT. These factors may influence further decision of therapy and give us a better explanation and correlation with unsatisfactory visual acuities than with the S-OCT.

HINTERGRUND: Im Verlauf der hinteren Glaskorperabhebung kommt es neben den in der Literatur ausfuhrlich beschriebenen makularen und peripheren Glaskorpertraktionen auch zu Traktionen an der Papille des N.opticus. Diese papillovitrealen Traktionsstrange konnen durch Zug und Dehnungsbelastung auf die retinale Nervenfaserschicht den Verlauf einer Optikusatrophie beinflussen. PATIENTEN UND METHODE: Ein 78-jahriger Patient leidet an einer progredienten Optikusatrophie am linken Auge trotz normaler Augendruckwerte. Seit zwei Jahren verschlechtern sich Visus und Gesichtsfeldbefund kontinuierlich. Klinisch und in den Untersuchungen mittels Optischer Koharenz Tomographie (OCT) zeigten sich deutliche papillovitreale Traktionsstrange vor allem im superior, nasalen Bereich der Papille. RESULTATE: Die papillovitrealen Traktionsstrange konnten im OCT eindeutig dargestellt werden. Im Ultrahigh Resolution OCT (UHR-OCT) zeigten sich spannungsbedingte, cystische Strukturen in der Ganglienzell- und Nervenfaserschicht an den Stellen der starksten Anhaftung der Traktionsstrange. Bei konstantem Fernvisus verringerte sich der Nahvisus von 0.3 logRAD auf 0.9 logRAD innerhalb eines Jahres. Im Gesichtsfeld (GF) bildete sich ein deutlich progredienter Ausfall der beiden unteren Quadranten intermediar, dem starksten Anhaftungsbereich der Traktionsstrange entsprechend. DISKUSSION: Der progrediente Gesichtsfeldausfall und die Visusverschlechterung sprechen fur eine chronische Schadigung des N.opticus an der Papille durch die papillovitrealen Traktionsstrange. Durch die von den Traktionsstrangen ausgeubten Zugkrafte kommt es zu einer Elongation, Dehnung und zu einer Abnahme im Axondurchmesser. Die anterograde und retrograde axoplasmatische Leitung wird gestort und die Progredienz der Optikusatrophie gefordert. Die Zugbelastung an den Aa.ciliares posteriores fuhrt zu einer Minderperfusion die sich in einer deutlichen Abblassung der Papille zeigt.

ZIELSETZUNG: Die Entwicklung eines neuen Darstellungssystems fur die dreidimensionale Visualisierung von Schichtbildaufnahmen in der Augenheilkunde. Im Speziellen, ein System das B-Mode-Scan-Datensatze von einer ultrahochauflosenden optischen Koharenztomographie-untersuchung als plastische dreidimensionale Objekte darstellen kann. METHODE: Im Rendering- und Raytracing-Programm Cinema 4D XL 9.102 Studio Bundle (Maxon Computer GmbH, Friedrichsburg, Deutschland) wurden mehrere "Subroutinen" programmiert die Schichtbildaufnahmen zu dreidimensionalen Darstellungen verarbeiten konnen. Es wurden von Patienten mit verschiedenen Netzhauterkrankungen ultrahochauflosende optische Koharenztomographien aufgenommen, und mit den programmierten "Subroutinen" zu dreidimensionalen Objekten weiterverarbeitet. Alle ultrahochauflosenden optischen Koharenztomographie-Untersuchungen wurden mit einem Ultrabreitband (160 nm) Titan:Saphire basierten Femtosecunden-Laser-System (INTEGRAL, Femtolasers Productions GmbH, Vienna, Austria) mit einer axialen Auflosung von 3 μm durchgefuhrt. RESULTATE: Es wurde ein neues dreidimensionales Darstellungssystem fur Schichtbildaufnahmen in der Augenheilkunde entwickelt das eine sehr plastische Darstellung von physiologischen und pathologischen Strukturen in der Netzhaut erlaubt. Das System zeichnet sich zusatzlich durch eine hohe Interaktivitat sowie durch eine grose Anpassungsfahigkeit aus. SCHLUSSFOLGERUNG: Das neue Darstellungssystem erlaubt die Visualisierung von physiologischen und pathologischen Strukturen der Netzhaut in einer Art und Weise, die uns neue Einsicht uber deren Morphologien und Entwicklungen geben wird.

Retinal laser photocoagulation represents a widely used treatment for retinal pathologies such as diabetic chorioretinopathy or diabetic edema. For effective treatment, an appropriate choice of the treatment energy dose is crucial to prevent excessive tissue damage caused by over-irradiation of the retina. In this manuscript we investigate simultaneous and time-resolved optical coherence tomography for its applicability to provide feedback to the ophthalmologist about the introduced retinal damage during laser photocoagulation. Time-resolved and volumetric optical coherence tomography data of 96 lesions on ex-vivo porcine samples, set with a 577 nm laser prototype and irradiance of between 300 and 8800 W/cm2 were analyzed. Time-resolved scans were compared to volumetric scans of the lesion and correlated with ophthalmoscopic visibility. Lastly, image parameters extracted from optical coherence tomography Mscans, suitable for lesion classification were identified. Results presented in this work support the hypothesis that simultaneous optical coherence tomography provides valuable information about the extent of retinal tissue damage and may be used to guide retinal laser photocoagulation in the future.

A compact fiber based spectrometer for biomedical application utilizing a tilted fiber Bragg grating (TFBG) as integrated dispersive element is demonstrated. Based on a 45° UV written PS750 TFBG a refractive spectrometer with 2.06 radiant/µm dispersion and a numerical aperture of 0.1 was set up and tested as integrated detector for an optical coherence tomography (OCT) system. Featuring a 23 mm long active region at the fiber the spectrum is projected via a cylindrical lens for vertical beam collimation and focused by an achromatic doublet onto the detector array. Covering 740 nm to 860 nm the spectrometer was optically connected to a broadband white light interferometer and a wide field scan head and electronically to an acquisition and control computer. Tomograms of ophthalmic and dermal samples obtained by the frequency domain OCT system were obtained achieving 2.84 µm axial and 7.6 µm lateral resolution. © (2014) COPYRIGHT Society of Photo Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Optical coherence tomography (OCT) is a noninvasive, three-dimensional imaging modality with several medical and industrial applications. Integrated photonics has the potential to enable mass production of OCT devices to significantly reduce size and cost, which can increase its use in established fields as well as enable new applications. Using silicon nitride (Si3N4) and silicon dioxide (SiO2) waveguides, we fabricated an integrated interferometer for spectrometer-based OCT. The integrated photonic circuit consists of four splitters and a 190 mm long reference arm with a foot-print of only 10 × 33 mm(2). It is used as the core of a spectral domain OCT system consisting of a superluminescent diode centered at 1320 nm with 100 nm bandwidth, a spectrometer with 1024 channels, and an x-y scanner. The sensitivity of the system was measured at 0.25 mm depth to be 65 dB with 0.1 mW on the sample. Using the system, we imaged human skin in vivo. With further optimization in design and fabrication technology, Si3N4/SiO2 waveguides have a potential to serve as a platform for passive photonic integrated circuits for OCT.

Optical coherence tomography (OCT) has revolutionises the diagnosis of retinal disease based on the detection of microscopic rather than subcellular changes in retinal anatomy. However, currently the technique is limited to the detection of microscopic rather than subcellular changes in retinal anatomy. However, coherence based imaging is extremely sensitive to both changes in optical contrast and cellular events at the micrometer scale, and can generate subtle changes in the spectral content of the OCT image. Here we test the hypothesis that OCT image speckle (image texture) contains information regarding otherwise unresolvable features such as organelle changes arising in the early stages of neuronal degeneration. Using ultrahigh resolution (UHR) OCT imaging at 800 nm (spectral width 140 nm) we developed a robust method of OCT image analyses, based on spatial wavelet and texture-based parameterisation of the image speckle pattern. For the first time we show that this approach allows the non-invasive detection and quantification of early apoptotic changes in neurons within 30 min of neuronal trauma sufficient to result in apoptosis. We show a positive correlation between immunofluorescent labelling of mitochondria (a potential source of changes in cellular optical contrast) with changes in the texture of the OCT images of cultured neurons. Moreover, similar changes in optical contrast were also seen in the retinal ganglion cell- inner plexiform layer in retinal explants following optic nerve transection. The optical clarity of the explants was maintained throughout in the absence of histologically detectable change. Our data suggest that UHR OCT can be used for the non-invasive quantitative assessment of neuronal health, with a particular application to the assessment of early retinal disease.

We present a multi-channel spectrometer that allows simultaneous acquisition of up to eight channels in order to perform parallel optical coherence tomography or low coherence interferometry. The rigid and compact design is employed in polarization sensitive optical coherence tomography measurements. Furthermore it is employed in distances and wedgeangle measurements between two glass slides. The spectrometer operates at a central wavelength of 835 nm and at a spectral bandwidth of 45 nm. This facilitates an axial resolution of 7.7 μm. The key feature is the simultaneous acquisition of up to eight channels, at a maximum frame rate of 6.5 kHz. The sensitivity is 91 dB at an integration time of 11 μs and an optical power of 0.7 mW at each of the sample arms. We obtained polarization sensitive OCT images of technical and biological samples and investigated the system inherent phase stability to multipoint low coherence interferometry measurements.

Optical coherence tomography (OCT) has enabled clinical applications that revolutionized in vivo medical diagnostics. Nevertheless, its current limitations owing to cost, size, complexity, and the need for accurate alignment must be overcome by radically novel approaches. Exploiting integrated optics, we assemble the central components of a spectral-domain OCT system on a silicon chip. The spectrometer comprises an arrayed-waveguide grating with 136-nm free spectral range and 0.21-nm wavelength resolution. The beam splitter is realized by a non-uniform adiabatic coupler with its 3-dB splitting ratio being nearly constant over 150 nm. With this device whose overall volume is 0.36 cm(3) we demonstrate high-quality in vivo imaging in human skin with 1.4-mm penetration depth, 7.5-µm axial resolution, and a signal-to-noise ratio of 74 dB. Considering the reasonable performance of this early OCT on-a-chip system and the anticipated improvements in this technology, a completely different range of devices and new fields of applications may become feasible.

A two stage statistical model based on texture and shape for fully automatic choroidal segmentation of normal and pathologic eyes obtained by a 1060 nm optical coherence tomography (OCT) system is developed. A novel dynamic programming approach is implemented to determine location of the retinal pigment epithelium/ Bruch’s membrane /choriocapillaris (RBC) boundary. The choroid–sclera interface (CSI) is segmented using a statistical model. The algorithm is robust even in presence of speckle noise, low signal (thick choroid), retinal pigment epithelium (RPE) detachments and atrophy, drusen, shadowing and other artifacts. Evaluation against a set of 871 manually segmented cross-sectional scans from 12 eyes achieves an average error rate of 13%, computed per tomogram as a ratio of incorrectly classified pixels and the total layer surface. For the first time a fully automatic choroidal segmentation algorithm is successfully applied to a wide range of clinical volumetric OCT data.

The recent expansion of clinical applications for optical coherence tomography (OCT) is driving the development of approaches for consistent image acquisition. There is a simultaneous need for time-stable, easy-to-use imaging targets for calibration and standardization of OCT devices. We present calibration targets consisting of three-dimensional structures etched into nanoparticle-embedded resin. Spherical iron oxide nanoparticles with a predominant particle diameter of 400 nm were homogeneously dispersed in a two part polyurethane resin and allowed to harden overnight. These samples were then etched using a precision micromachining femtosecond laser with a center wavelength of 1026 nm, 100kHz repetition rate and 450 fs pulse duration. A series of lines in depth were etched, varying the percentage of inscription energy and speed of the translation stage moving the target with respect to the laser. Samples were imaged with a dual wavelength spectral-domain OCT system and point-spread function of nanoparticles within the target was measured.

To map choroidal (ChT) and retinal thickness (RT) in healthy subjects and patients with diabetes with and without maculopathy using three dimensional 1060-nm optical coherence tomography (3D-1060nm-OCT).Sixty-three eyes from 42 diabetic subjects (41-82 years of age; 11 females) grouped according to a custom scheme using Early Treatment Diabetic Retinopathy Study definitions for pathology within 1 disc-diameter of fovea (without pathology [NDR], microaneurysms [M1], exudates [M2], clinically significant macular edema [CSME]) and 16 eyes from 16 healthy age matched subjects (38-79 years of age; 11 females) were imaged by 3D-1060nm-OCT performed over a 36° × 36° field of view. Axial length, 45° fundus photographs, body mass index, plasma glucose, and blood pressure measurements were recorded. The ChT at the subfoveal location and ChT maps between RPE and the choroidal-scleral interface were generated and statistically analyzed.RT maps show thinning in the NDR group but an increase in thickness with increasing maculopathy in the temporal and central regions (unpaired t-test; P0.05). ChT mapping of all diabetic patients revealed central and inferior thinning compared to healthy eyes (unpaired t-test; P0.001). Subfoveal ChT (mean ± SD) for healthy eyes was 327 ± 74 μm, which was significantly thicker than all diabetic groups (214 ± 55 μm for NDR, 208 ± 49 μm for M1, 205 ± 54 μm for M2, and 211 ± 76 μm for CSME (ANOVA P0.001; Tukey P0.001).3D-1060nm-OCT has shown that the central choroid is thinner in all type 2 diabetic eyes regardless of disease stage. The choroidal thinning may exceed the magnitude of possible choriocapillaris atrophy. In contrast to the conventional assessment of pathologic thickness change in several locations, thickness maps allow investigation of the choroid over the extent of affected areas.

The dispersion mismatch between sample and reference arm in frequency-domain OCT can be used to iteratively suppress complex conjugate artifacts and thereby increase the imaging range. We propose a fast dispersion encoded full range (DEFR) algorithm that detects multiple signal components per iteration. The influence of different dispersion levels on the reconstruction quality is analyzed for in vivo retinal tomograms at 800 nm. Best results have been achieved with about 30 mm SF11, with neglectable resolution decrease due to finite resolution of the spectrometer. Our fast DEFR algorithm achieves an average suppression ratio of 55 dB and converges within 5 to 10 iterations. The processing time on non-dedicated hardware was 5 to 10 seconds for tomograms with 512 depth scans and 4096 sampling points per depth scan. Application of DEFR to the more challenging 1060 nm wavelength region is demonstrated by introducing an additional optical fibre in the sample arm.

A novel non-invasive in vivo multimodal optical coherence tomography (OCT)/photoacoustic tomography (PAT) imaging system capable of obtaining structural and functional information simultaneously has been demonstrated in skin. A 1060 nm OCT system acquiring 47k depth-scans/s with ~ 7 μm axial and ~ 20 μm transverse resolutions has been incorporated into a backward-mode PA system based on a planar, optically-transparent Fabry-Perot interferometer (FPI) sensor. In this study, the excitation wavelength was set to 670 nm and a focused laser beam at 1550 nm was used as the sensor interrogation beam. OCT and PAT images were obtained sequentially and the coregistered images were combined to form the final 3D image. OCT/PAT images obtained in vivo from the skin of a hairless mouse and human palmar skin demonstrated the ability of this multimodal imaging system to provide complementary structural and functional information from deeper depths with increased contrast.

Purpose: To compare retinal thickness and choroidal thickness at increasing retinal eccentricity in individuals with early age-related macular degeneration (AMD) and in healthy controls using enhanced choroidal penetration, 3-dimensional optical coherence tomography at 1060 nm.\ud \ud Design: Cross-sectional study.\ud \ud Methods: Individuals with early AMD (n = 16; mean age, 71.6 ± 8.5 years) and a comparison group of healthy controls (n = 16; 67.6 ± 5.4 years) were recruited. Three-dimensional (20 degrees × 20 degrees) long-wavelength optical coherence tomography (1060 nm) images (approximately 8-μm axial resolution; 47 000 A scans/second, centered on the fovea) were obtained from all participants after pupil dilation. Retinal thickness was measured between the inner limiting membrane and the retinal pigment epithelium. Choroidal thickness was measured between the retinal pigment epithelium and the choroid–scleral interface. Thickness measurements were obtained subfoveally and at 0.5-mm intervals to a maximum of 2.0 mm nasally, temporally, superiorly, and inferiorly. The main outcome measures were retinal and choroidal thickness (measured in micrometers) at different eccentricities on vertical and horizontal meridians.\ud \ud Results: Mean retinal thickness was reduced significantly in the group of participants with early AMD compared with the control group at multiple locations within 2.0 mm of the fovea. This difference was most significant at the fovea, where the mean retinal thickness of the early AMD group was 179 ± 27 μm and that of the control group was 202 ± 18 μm (P = .008). There was no significant difference in choroidal thickness between groups at any location.\ud \ud Conclusions: Retinal thickness is reduced in early AMD, but choroidal thickness seems to be unaffected by the early disease process.

A novel combined photoacoustic tomography (PAT), optical resolution photoacoustic microscopy (ORPAM) and optical coherence tomography (OCT) instrument has been developed for imaging biological tissues. The system is based on the use of a Fabry-Perot (FP) polymer film ultrasound sensor. This is designed to be transparent to wavelengths between 590nm and 1200nm so that photoacoustic excitation laser pulses in this spectral range can be transmitted through the sensor into the underlying tissue to allow backward mode operation. The dual PAT-ORPAM capability of the system was demonstrated by imaging a tissue phantom composed of 7μm diameter carbon fibres immersed in an optically scattering liquid. The lateral and vertical spatial resolutions in ORPAM mode are approximately 7μm and 10μm respectively for sub-mm depths. In PAT mode, the lateral spatial resolution is less than 50μm for depths up to 5mm and the vertical resolution is approximately 10μm. The transparent nature of the FP polymer film ultrasound sensor offers a convenient platform for combining other optical imaging modalities with PAT and ORPAM. To illustrate this, a frequency-domain OCT system operating at 1060nm was integrated into the system and combined PAT/OCT images of the skin of a mouse were obtained in vivo.

Weakly scattering tree shrew retina has been imaged in vitro with full field swept source optical coherence tomography, visualising multiple intraretinal layers. The system utilises a 50nm bandwidth Superlum SLD, to acheive ~8μm of axial resolution and 4μm of transversal resolution. Volumetric images of retinal tissue with dimensions of 1248x936x678μm (horizontal by vertical by axial) were recorded in two second (equivalent of 153,600 A-scans per second) with a measured signal to noise ratio of 75dB. From the 5mW of SLD optical power available, 720μW illuminates the sample, giving a power per pixel of 4.6nW, ten times less power per pixel then standard FDOCT systems. After upgrading the camera and redesigning the optical beam path, 82dB of SNR was realised.

Conventionally, cell chemotaxis is studied on two-dimensional (2D) transparent surfaces due to limitations in optical and image data-collection techniques. However, substrates which more closely mimic the natural environment of cells are often opaque or three-dimensional (3D). The non-invasive label-free imaging technique of frequency domain optical coherence tomography (OCT) has high axial and transverse resolution of >4μm, comparatively high penetration depth and the ability to acquire volumes in a few seconds, therefore offering the potential to visualize moving cells in 3D (2D+time) and 4D (3D+time). Cell migration is demonstrated in 3D on opaque surfaces, and in 4D within an agarose gel. The speed and directionality of wild type (Ax2) cell movement is seen to be comparable on agar and nitrocellulose filter substrates. Differences can be clearly seen in the character of cell movement between Ax2, myosin knockout (mhcA-) and PLC null ~10μm Dictyostelium discoideum cells in 4D using ultrahigh resolution OCT. OCT is therefore shown to be a useful technique for the study of cell migration.

In this study, depth resolved measurements of absorption profiles in the wavelength range of 800 nm with a bandwidth of 140 nm are demonstrated using high speed spectroscopic frequency domain OCT (SOCT). With proper calibration, SOCT is able to extract absolute, depth resolved absorption profiles over the whole wavelength range at once without the need of tuning and performing measurements at single wavelengths sequentially. In addition, high acquisition speed in excess of 20 kHz allows to measure absorption dynamics with 50 µs time resolution, which might be useful for the investigation of pharmacokinetics or pharmacodynamics. SOCT of ∼600 µm thick single- and multilayered, weakly scattering phantoms with varying absorption in the range of 10–60 cm-1, equivalent to blood absorption in capillaries, is presented. SOCT measurements are compared with those using a spectrometer in transmission mode. For Indocyanine Green (ICG), a dynamic absorption measurement is demonstrated.

Ultrahigh axial resolution surface profiling as well as volumetric optical imaging based on time encoded optical coherence tomography in the frequency domain without any mechanical scanning element is presented. A frequency tuned broad bandwidth titanium sapphire laser is interfaced to an optical microscope (Axioskop 2 MAT, Carl Zeiss Meditec) that is enhanced with an interferometric imaging head. The system is equipped with a 640 x 480 pixel CMOS camera, optimized for the 800 nm wavelength tuning range for transmission and reflection measurements of a microscopic sample. Sample volume information over 1.3 x 1 x 0.2 mm(3) with ~3 mum axial and ~4 mum transverse resolution in tissue is acquired by a single wavelength scan over more than 100 nm optical bandwidth from760 to860 nm with 128-2048 equidistant optical frequency steps with an acquisition time of 1 to 50 ms per step. Topography and tomography with a signal to noise ratio of 83 dB is demonstrated on test surfaces and biological specimen respectively. This novel OCT technique promises to enable high speed, three dimensional imaging by employing high frame rate cameras and state of the art tunable lasers in a mechanically stable environment, due to lack of moving components while reducing the intensity on the sample.

Conventionally, cell chemotaxis is studied on two-dimensional (2D) transparent surfaces, due to limitations in optical and image data-collection techniques. However, surfaces that more closely mimic the natural environment of cells are often opaque. Optical coherence tomography (OCT) is a noninvasive label-free imaging technique, which offers the potential to visualize moving cells on opaque surfaces and in three dimensions (3D). Here, we demonstrate that OCT is an effective means of time-lapse videomicroscopy of Dictyostelium cells undergoing 3D (2D+time) cell migration on nitrocellulose substrates and 4D (3D+time) chemotaxis within low-density agarose gels. The generated image sequences are compatible with current computer-based image-analysis software for quantification of cell motility. This demonstrates the utility of OCT for cell tracking and analysis of cell chemotaxis in complex environments. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Purpose To demonstrate acquisition and analysis methods for depth-resolved observation of slow retinal physiology induced changes in infrared backscatter in vivo. Methods A dark-adapted human was briefly subjected to a localized photobleach. For 20 min before and 30 min after the stimulus, volumetric optical coherence tomograms were collected partially overlapping the bleached region. Tomograms were segmented into retinal layers by a newly described algorithm exploiting information in adjacent B-scans. En face fundus images extracted from major intraretinal layers were laterally registered manually. Time series summarizing the observed backscatter in selected layers for the bleached and unbleached areas are shown with a variety of corrections and normalizations applied: tomograms were corrected for inherent sensitivity roll-off, and the ratio between other layers and an assumed unchanging layer (retinal pigment epithelium), as well as the ratio of the stimulated area to the unstimulated area, were calculated. Results Adjacent B-scan information allows a simpler segmentation algorithm to be used. Sensitivity roll-off correction reduces signal variability due to eye motion. After normalizations, the signal correlated with the stimulus appears strongest at the photoreceptor inner-outer segment junction. Conclusions Demonstrated methods manage data complexity and reduce uncorrelated signal variability. This single trial warrants further investigation of intrinsic optical signals to observe slow physiologic responses.

The amount of light backscattered from neural tissues changes as a function of activation and is the basis of intrinsic optical signal (IOS). Typically IOS is observed by looking at darkfield scatter with a CCD camera. The retina is a calculating portion of the central nervous grey matter with an optical quality window, and is likewise easily stimulated optically. Therefore the retina makes a natural model for observing neural interactions with optical tools. Optical coherence tomography (OCT) is an imaging modality that provides depth resolved maps of the amount of light backscattered from tissue that has wide clinical use for observing structural defects associated with ophthalmic disease. It is therefore also natural to use OCT as means to observe intrinsic optical signal in the retina. Indeed, OCT has recently been used to observe an increase in backscatter at the level of the outer photoreceptor segment after bleaching light stimulation in an excised rabbit retina. We are currently attempting to translate this result towards a diagnostic technique for photoreceptor dysfunction in human patients. Currently patient motion and physiological noise present barriers that must be overcome with increases in technological and experimental sophistication. This proceeding reviews current understanding of retinal intrinsic optical signal and discusses its measurement challenge.

Biomedical Imaging Group, School of Optometry & Vision Sciences,Cardiff University, Wales, UKAbstract. Ultra-high speed optical coherence tomography employing an ultra-broadband lightsource has been combined with adaptive optics utilizing a single high stroke deformable mirrorandchromaticaberrationcompensation. Thereductionofmotionartefacts,geometricandchro-matic aberrations (pancorrection) permits to achieve an isotropic resolution of 2 3 µminthehuman eye. The performance of this non-invasive imaging modality enables to resolve cellularstructuresincludingconephotoreceptors, nerve“brebundlesandcollagenousplatesofthelam-ina cribrosa, and retinal pigment epithelial (RPE) cells in the human retina in vivo with superiordetail. Alterations of cellular morphology due to cone degeneration in a colour-blind subjectare investigated in ultra-high resolution with selective depth sectioning for the “rst time.Keywords: adaptive optics, achromatizer, pancorrection, photoreceptors, retinal pigment ep-ithelial (RPE) cells, lamina cribrosa, colour-blind, retinal pathology

Cellular in vivo visualization of the three dimensional architecture of individual human foveal cone photoreceptors is demonstrated by combining ultrahigh resolution optical coherence tomography and a novel adaptive optics modality. Isotropic resolution in the order of 2-3 microm, estimated from comparison with histology, is accomplished by employing an ultrabroad bandwidth Titanium:sapphire laser with 140 nm bandwidth and previous correction of chromatic and monochromatic ocular aberrations. The latter, referred to as pancorrection, is enabled by the simultaneous use of a specially designed lens and an electromagnetically driven deformable mirror with unprecedented stroke for correcting chromatic and monochromatic aberrations, respectively. The increase in imaging resolution allows for resolving structural details of distal elements of individual foveal cones: inner segment zones--myoids and ellipsoids--are differentiated from outer segments protruding into pigment epithelial processes in the retina. The presented technique has the potential to unveil photoreceptor development and pathogenesis as well as improved therapy monitoring of numerous retinal diseases.

Spectrometer based optical coherence tomography at 1050nm with >70nm of spectral bandwidth, acquiring 48k depth scans per second for deeper penetration and isotropic visualisation of the full three dimensional choroidal vasculature is demonstrated in vivo.

The integration of adaptive optics and an achromatizing lens into an ultra-high resolution OCT system enables three-dimensional imaging of photoreceptor morphology. Optophysiology might lead to the extraction of depth-resolved information about retinal function.

We demonstrated that the dispersion of scanning microscope optics (including a Zeiss 40x/1.2 Apochromat objective) can be compensated by means of chirped mirrors over a bandwidth of 170 nm at 800 nm. The interferometric autocorrelation trace recorded at the focus of the microscope objective with a two-photon diode indicated a pulse duration of < 12 fs. The propagation time difference of the system can be minimized by proper choice of the components, enabling sub-12-fs pulse delivery with a completely filled 40x/0.8 Zeiss Achroplan water immersion objective.