Simultaneous directional full-field OCT using path-length and carrier multiplexing.

Full-field swept-source optical coherence tomography (FF-SS-OCT) is an emerging technology with potential applications in ophthalmic imaging, microscopy, metrology, and other domains. Here we demonstrate a novel method of multiplexing FF-SS-OCT signals using carrier modulation (CM). The principle of CM could be used to inspect various properties of the scattered light, e.g. its spectrum, polarization, Doppler shift, or distribution in the pupil. The last of these will be explored in this work, where CM was used to acquire images passing through two different optical pupils. The two pupils contained semicircular optical windows with perpendicular orientations, with each window permitting measurement of scattering anisotropy in one dimension by inducing an optical delay between the images formed by the two halves of the pupil. Together, the two forms of multiplexing permit measurement of differential scattering anisotropy in the x and y dimensions simultaneously. To demonstrate the feasibility of this technique our carrier multiplexed directional FF-OCT (CM-D-FF-OCT) system was used to acquire images of a microlens array, human hair, onion skin and in vivo human retina. The results of these studies are presented and briefly discussed in the context of future development and application of this technique.

Single-shot multi-depth full-field optical coherence tomography using spatial frequency division multiplexing.

Fast 3D volumetric imaging has been essential for biology, medicine and industrial inspections, and various optical coherence tomography (OCT) methods have been developed to meet such needs. Point-scanning based approaches, such as swept-source OCT and spectral domain OCT, can obtain a depth information at once, but they require lateral scan for full 3D imaging. On the contrary, full-field OCT needs the scanning of imaging depth while it records a full lateral information at once. Here, we present a full-field OCT system that can obtain multi-depth information at once by a single-shot recording. We combine a 2D diffraction grating and a custom-made echelon to prepare multiple reference beams having different pathlengths and propagating angles. By recording a single interference image between the reflected wave from a sample and these multiple reference beams, we reconstruct full-field images at multiple depths associated with the pathlengths of the individual reference beams. We demonstrated the single-shot recording of 7 different depth images at 10 µm for biological tissues. Our method can potentially be useful for applications where high-speed recording of multiple en-face images is crucial.

Determining Optic Nerve Cupping Using Optical Coherence Tomography (OCT) Versus a New Electronic Mobile Device.

PURPOSE: We present a new device that may aid in glaucoma screening. The vertical cup-to-disc ratio (CDR) obtained from a new electronic mobile device (EMD) was compared with that obtained from a spectral-domain optical coherence tomography. In addition, results from examiner's evaluations were compared with the results mentioned above. METHODS: A single-masked study was performed to evaluate the CDR results from 110 eyes from 110 subjects whose ages ranged between 18 and 60 years (39±13 y old), of whom 66 (60%) were female individuals. Vertical CDR was analyzed 5 times with each device in a single visit and evaluated by 3 different ophthalmologists. The Spearman correlation test and Bland-Altman analysis were used to evaluate the correlation and agreement between methods. RESULTS: The CDR average using spectral-domain optical coherence tomography was 0.47±0.04, whereas the CDR average using EMD was 0.42±0.02. The clinical evaluation resulted in an average of 0.34±0.27. The Spearman test showed a strong correlation between vertical CDR obtained with both devices (r=0.8319; P<0.0001) and between EMD and the examiners (r=0.7156; P>0.001). Bland-Altman analysis showed good agreement between both devices as well as between EMD and the examiners (95% limits of agreement from -0.20 to 0.10 and from -0.15 to 0.30, respectively). CONCLUSIONS: We present a low-cost, reliable EMD that may serve as an alternative to subjectively measuring vertical CDR in face-to-face consultations and hence increase the general public's access to glaucoma screening. This may be especially useful for patients who live in remote areas.

Hand-held Optical Coherence Tomography Monitoring of Submillimeter Retinoblastoma Treated with Indocyanine Green-enhanced Transpupillary Therapy.

Over recent years, hand-held optical coherence tomography (HH-OCT) has become critical for retinoblastoma diagnosis and management. We report precise HH-OCT findings in a case of sub-millimeter retinoblastoma treated with foveal-sparing indocyanine green-enhanced transpupillary thermotherapy (ICG-TTT). A 2-month-old Caucasian female with bilateral Group B retinoblastoma showed two recurrent macular tumors in the right eye, demonstrating 88 µm and 37 µm of growth to 344 µm and 413 µm in thickness, respectively, on HH-OCT. Each was treated with additional intravenous chemotherapy and foveal-sparing ICG-TTT. Tumor regression to 154 µm and 224 µm was documented on HH-OCT and maintained on follow-up. HH-OCT is vital in confirming clinical findings and influencing management decisions in retinoblastoma. In this case, HH-OCT precisely documented submillimeter retinoblastoma recurrence and treatment response.

Optical Coherence Tomography to Measure Sound-Induced Motions Within the Mouse Organ of Corti In Vivo.

The measurement of mechanical vibrations within the living cochlea is critical to understanding the first nonlinear steps in auditory processing, hair cell stimulation, and cochlear amplification. However, it has proven to be a challenging endeavor. This chapter describes how optical coherence tomography (OCT) can be used to measure vibrations within the tissues of the organ of Corti. These experimental measurements can be performed within the unopened cochlea of living mice routinely and reliably.

Clinical Factors Associated with Lamina Cribrosa Thickness in Patients with Glaucoma, as Measured with Swept Source Optical Coherence Tomography.

PURPOSE: To investigate the influence of various risk factors on thinning of the lamina cribrosa (LC), as measured with swept-source optical coherence tomography (SS-OCT; Topcon). METHODS: This retrospective study comprised 150 eyes of 150 patients: 22 normal subjects, 28 preperimetric glaucoma (PPG) patients, and 100 open-angle glaucoma patients. Average LC thickness was determined in a 3 x 3 mm cube scan of the optic disc, over which a 4 x 4 grid of 16 points was superimposed (interpoint distance: 175 µm), centered on the circular Bruch's membrane opening. The borders of the LC were defined as the visible limits of the LC pores. The correlation of LC thickness with Humphrey field analyzer-measured mean deviation (MD; SITA standard 24-2), circumpapillary retinal nerve fiber layer thickness (cpRNFLT), the vertical cup-to-disc (C/D) ratio, and tissue mean blur rate (MBR) was determined with Spearman's rank correlation coefficient. The relationship of LC thickness with age, axial length, intraocular pressure (IOP), MD, the vertical C/D ratio, central corneal thickness (CCT), and tissue MBR was determined with multiple regression analysis. Average LC thickness and the correlation between LC thickness and MD were compared in patients with the glaucomatous enlargement (GE) optic disc type and those with non-GE disc types, as classified with Nicolela's method. RESULTS: We found that average LC thickness in the 16 grid points was significantly associated with overall LC thickness (r = 0.77, P < 0.001). The measurement time for this area was 12.4 ± 2.4 minutes. Average LC thickness in this area had a correlation coefficient of 0.57 with cpRNFLT (P < 0.001) and 0.46 (P < 0.001) with MD. Average LC thickness differed significantly between the groups (normal: 268 ± 23 µm, PPG: 248 ± 13 µm, OAG: 233 ± 20 µm). Multiple regression analysis showed that MD (ß = 0.29, P = 0.013), vertical C/D ratio (ß = -0.25, P = 0.020) and tissue MBR (ß = 0.20, P = 0.034) were independent variables significantly affecting LC thickness, but age, axial length, IOP, and CCT were not. LC thickness was significantly lower in the GE patients (233.9 ± 17.3 µm) than the non-GE patients (243.6 ± 19.5 µm, P = 0.040). The correlation coefficient between MD and LC thickness was 0.58 (P < 0.001) in the GE patients and 0.39 (P = 0.013) in the non-GE patients. CONCLUSION: Cupping formation and tissue blood flow were independently correlated to LC thinning. Glaucoma patients with the GE disc type, who predominantly have large cupping, had lower LC thickness even with similar glaucoma severity.

Cierre angular secundario al uso de lorazepam en paciente con miopía magna / Angle closure secondary to the use of lorazepam in patient with myopia magna

CASO CLÍNICO: Miope magna con cámara anterior estrecha que presentó cierre angular secundario a lorazepam. DISCUSIÓN: El cierre angular generalmente ocurre en pacientes predispuestos desencadenado por factores precipitantes. Muchos fármacos de uso rutinario en la práctica clínica podrían ejercer como factor responsable del cierre angular secundario

CASE REPORT: Myopic magna with narrow anterior chamber that presented with a secondary angle closure due to lorazepam. DISCUSSION: Angle closure usually occurs in predisposed patients and is triggered by precipitating factors. Many drugs routinely used in clinical practice could act as a factor responsible for the secondary angle closure

Métodos de examen en oftalmología para apoyo del diagnóstico y seguimiento en la enfermedad de Alzheimer leve o moderada / Ophthalmological examination for diagnosis and follow-up in mild and moderate Alzheimer disease

Objetivos: evaluar si existen alteraciones en la función visual y en la estructura de la retina y del nervio óptico en pacientes con demencia de tipo Alzheimer (DA). Material y métodos: se incluyeron 61 pacientes con DA leve-moderada y 36 controles sanos. En todos ellos se evaluó la agudeza visual (escala ETDRS), la sensibilidad al contraste (con los tests CSV-1000E y Pelli-Robson), la estereopsis (con el test TNO) y la visión cromática (con los tests Farnsworth 15 D y Lanthony 15 D utilizando el software Vision Color Recorder). La estructura y los espesores de la retina y del nervio óptico se evaluaron mediante tomografía de coherencia óptica (OCT). Comparamos los resultados entre pacientes y controles. Resultados: el grupo de pacientes mostró una disminución estadísticamente significativa en la agudeza visual, la sensibilidad al contraste, la visión cromática y los espesores de las nueve áreas maculares y de la capa de fibras nerviosas de la retina. Conclu siones: la DA causa alteraciones en la función visual así como una reducción de los espesores en la retina y el nervio óptico desde estadios iniciales de la enfermedad. Estos parámetros podrían ser buenos biomarcadores para el diagnóstico y seguimiento de esta enfermedad (AU)

Objective: To analyze visual function alterations and changes in the retina and the optic nerve in mild or moderate Alzheimer disease (AD) patients, compared with healthy subjects. Material and methods: Sixty one mild/moderate AD patients and 36 age-and-sex matched controls were included. All of them underwent assessment of visual acuity (ETDRS scale), contrast sensitivity (CSV-1000E and Pelli-Robson tests), stereopsis (TNO test), and color vision (Farnsworth 15 D and Lanthony 15 D tests using the Vision Color Recorder software). Optical coherence tomography (OCT) of the macula and optic disc was also acquired to evaluate macular and the retinal nerve fiber layer (RNFL) thicknesses. Comparison between patients and healthy controls were analyzed. Results: AD group showed statistical significant decrease in visual acuity, contrast sensitivity color vision, macular thicknesses in the 9 analyzed areas and RNFL thickness. Conclusions: Visual function alterations and reduction of macular and optic nerve thicknesses appear in AD patients since earlier stages. These parameters may be usefull as biomarker in diagnosis and follow-up of AD patients (AU)

Fiber-optic polarization diversity detection for rotary probe optical coherence tomography.

We report a polarization diversity detection scheme for optical coherence tomography with a new, custom, miniaturized fiber coupler with single mode (SM) fiber inputs and polarization maintaining (PM) fiber outputs. The SM fiber inputs obviate matching the optical lengths of the X and Y OCT polarization channels prior to interference and the PM fiber outputs ensure defined X and Y axes after interference. Advantages for this scheme include easier alignment, lower cost, and easier miniaturization compared to designs with free-space bulk optical components. We demonstrate the utility of the detection system to mitigate the effects of rapidly changing polarization states when imaging with rotating fiber optic probes in Intralipid suspension and during in vivo imaging of human airways.

Full-field optical coherence tomography using immersion Mirau interference microscope.

In this study, an immersion Mirau interference microscope was developed for full-field optical coherence tomography (FFOCT). Both the reference and measuring arms of the Mirau interferometer were filled with water to prevent the problems associated with imaging a sample in air with conventional FFOCT systems. The almost-common path interferometer makes the tomographic system less sensitive to environmental disturbances. En face OCT images at various depths were obtained with phase-shifting interferometry and Hariharan algorithm. This immersion interferometric method improves depth and quality in three-dimensional OCT imaging of scattering tissue.

Optical coherence tomography in paediatric glaucoma: time domain versus spectral domain.

BACKGROUND/AIMS: Spectral-domain (SD)- Optical Coherence Tomography (OCT) can track eye movements, has faster acquisition time and higher resolution than time-domain(TD)-OCT. The aim of the study was to assess the utility of SD-OCT in paediatric glaucoma and determine its agreement with TD-OCT. METHODS: Children who had SD-OCT(Spectralis, Heidelberg-Engineering,Germany) were retrospectively and prospectively identified from Duke paediatric glaucoma clinic. The peripapillary retinal nerve fibre layer (RNFL) and macular thickness and volume (MV) were compared amongst four groups: normal eyes, eyes with physiologic cupping (C:D >0.5 and <0.8, IOP <21), mild glaucomatous eyes (C:D <0.5, intra-ocular pressure (IOP) >21) and severe glaucoma (C:D>0.5, IOP>21). SD-OCT values were compared to TD-OCT(OCT-3, Carl-Zeiss-Meditec, Dublin, CA) values in a subset of subjects who had same day scans using both instruments. Children with neurologic disorders, refractive error >±5D, pseudophakia and prematurity were excluded. RESULTS: Included were 83 eyes of 83 children, mean age 11.9 ± 4.2 years. SD-OCT measurements of average RNFL thickness and MV differed among normals(n=24), physiologically cupped (n=31), mild (n=15) versus severe glaucoma (n=13): (RNFL:104 ± 9, 99 ± 6, 98 ± 9 vs 62 ± 18 µm, respectively, p<0.05; MV: 8.7 ± 0.3, 8.6 ± 0.3, 8.8 ± 0.4 vs 8.0 ± 0.6 mm³;, respectively, p<0.05). Same-day SD-OCT and TD-OCT measures in 53 eyes correlated linearly (RNFL r(2)=0.88; MVr(2)=0.58). SD-OCT measured lower RNFL and higher macular thickness than TD-OCT. Among eyes with severe glaucoma, 4 of 13 (30%) had unreliable TD-OCT but reliable SD-OCT. CONCLUSIONS: SD-OCT was easier to obtain than TD-OCT in children. SD-OCT and TD-OCT measurements correlated, but values were not interchangeable.

Refractive index measurement of acute rat brain tissue slices using optical coherence tomography.

An optical coherence tomography (OCT) system employing a microelectromechanical system (MEMS) mirror was used to measure the refractive index (RI) of anatomically different regions in acute brain tissue slices, in which viability was maintained. RI was measured in white-matter and grey-matter regions, including the cerebral cortex, putamen, hippocampus, thalamus and corpus callosum. The RI in the corpus callosum was found to be ~4% higher than the RIs in other regions. Changes in RI with tissue deformation were also measured in the cerebral cortex and corpus callosum under uniform compression (20-80% strain). For 80% strain, measured RIs increased nonlinearly by up to 70% and 90% in the cerebral cortex and corpus callosum respectively. Knowledge of RI in heterogeneous tissues can be used to correct distorted optical images caused by RI variations between different regions. Also deformation-dependent changes in RI can be applied to OCT elastography or to mechanical tests based on optical imaging such as indentation tests.

Determination of coherence length in biological tissues.

BACKGROUND AND OBJECTIVE: Lately in phototherapy the use of diodes instead of lasers was suggested for economical and practical reasons. It has been argued that lasers have no preference over diodes since they lose their coherence once penetrating biological tissues. However, this point has never been experimentally proven. In this work we, for the first time, have experimentally validated the conditions affecting the spatial coherence of a laser illumination going through a biological tissue. STUDY DESIGN/MATERIALS AND METHODS: In our experiments we measured the spatial coherence of the light passing through phantoms containing intralipid and ink component as well as through uncooked turkey meat. We do this measuring the changes of the contrast of the speckle patterns generated due to laser illumination. Flow tunnels inside the phantoms were generated by needles in two different diameters. The measurements were performed for varied integration time, varied thickness of phantoms, and for varied flow rates. The measurement system included two excitation sources: a green doubled Nd:YAG laser at wavelength of 532 nm and an ultra high power green LED at a wavelength of 520 nm. RESULTS: It was experimentally validated that the thickness of the tissue does not change the coherence while there is no flow. Furthermore, the flow velocity and the flow volumetric rate highly affect the coherence length. Previously developed mathematical expression, in which the contrast depends on the correlation and the exposure time, was found to be compatible with the obtained experimental results. CONCLUSIONS: We found that the coherence of the laser is not lost when the light goes through a static tissue but it is partially lost when there is a flow of fluid through the tissue. The volumetric flow rate is directly correlated to the loss of spatial coherence. Higher flow rate produces shorter coherence length.

Audio frequency in vivo optical coherence elastography.

We present a new approach to optical coherence elastography (OCE), which probes the local elastic properties of tissue by using optical coherence tomography to measure the effect of an applied stimulus in the audio frequency range. We describe the approach, based on analysis of the Bessel frequency spectrum of the interferometric signal detected from scatterers undergoing periodic motion in response to an applied stimulus. We present quantitative results of sub-micron excitation at 820 Hz in a layered phantom and the first such measurements in human skin in vivo.

Contrast improvement in Fourier-domain optical coherence tomography through time gating.

Time-gated (TG) Fourier-domain optical coherence tomography (FDOCT) exploits interferometric imaging with incoherent gating to filter out unwanted backreflections and improve contrast. The system uses sum-frequency generation with a variable length optical pulse as a "time gate" to restrict the depth field of view of backscattered light to 84-176 microm (-20 dB points). The imaging bandwidth is upconverted from the IR (1280 nm) to visible (504 nm), which allows the use of sensitive silicon-based detection technology, prior to standard FDOCT processing. The TG system achieves a maximum sensitivity of 88 dB, and a contrast enhancement of 29 dB is shown over a standard IR FDOCT system. Imaging of a highly scattering medium (onion skin) is also demonstrated.

Full-range, high-speed, high-resolution 1 microm spectral-domain optical coherence tomography using BM-scan for volumetric imaging of the human posterior eye.

An alternative optical coherence tomography (OCT) to clinical ophthalmic 830 nm spectral-domain OCTs (SD-OCT) is demonstrated. An axial resolution of 7.4 microm, ranging depth of 4.2 mm in tissue, sensitivity of 98.5 dB, and detection speed of 38,300 axial scans/s have been achieved. These are comparable or superior to those of recently commercially available ophthalmic 830 nm SD-OCTs in clinics. In addition, fast volumetric imaging for the in vivo human posterior eye with high-contrast of the choroid is achieved. A broadband 1.04 microm light source enables the high-contrast and high resolution imaging of the retina and choroid. The ranging depth is extended by applying a full-range imaging method with an electro-optic modulator (BM-scan method). A prototype high-speed InGaAs line scan camera with 1024 pixels is used. A newly reported sensitivity improvement property of the BM-scan method demonstrates a sensitivity enhancement of 5.1 dB. We also introduce a newly developed resampling calibration method of spectrum that is independent of the intrinsic dispersion mismatch of the interferometer. The three-dimensional structure of the in vivo human optic nerve head with a very deep cupping is successfully visualized.

Towards versatile coherent pulse synthesis using femtosecond laser and optical parametric oscillators.

Pulses from a tunable near-infrared femtosecond optical parametric oscillator and its Ti:sapphire pump laser were phase-locked by matching their carrier-envelope phase-slip frequencies to one quarter of their common pulse repetition frequency. Interferometric second-order cross-correlation and spectral interferometry traces demonstrated their mutual coherence for periods of at least 20 ms, compared with individual coherence times of 0.1 ms estimated from their phase-noise power spectra. This result is a prerequisite for versatile coherent pulse synthesis. Implications for the synthesis of arbitrary waveforms from multi-colour pulses are discussed.

Pulsed photothermal temperature profiling of agar tissue phantoms.

We determine experimentally the accuracy of pulsed photothermal radiometric (PPTR) temperature depth profiling in water-based samples. We use custom tissue phantoms composed of agar gel layers separated by very thin absorbing layers. Two configurations of the acquisition system are compared, one using the customary spectral band of the InSb radiation detector (3.0-5.5 microm) and the other with a spectrally narrowed acquisition band (4.5-5.5 microm). The laser-induced temperature depth profiles are reconstructed from measured radiometric signals using a custom minimization algorithm. The results correlate very well with phantom geometry as determined by optical coherence tomography (OCT) and histology in all evaluated samples. Determination of the absorbing layer depth shows good repeatability with spatial resolution decreasing with depth. Spectral filtering improves the accuracy and resolution, especially for shallow absorption layers (~120 microm) and more complex structures (e.g., with two absorbing layers). The average full width at half maximum (FWHM) of the temperature peaks equals 23% of the layer depth.

Time-domain optical coherence tomography with digital holographic microscopy.

We show that digital holography can be combined easily with optical coherence tomography approach. Varying the reference path length is the means used to acquire a series of holograms at different depths, providing after reconstruction images of slices at different depths in the specimen thanks to the short-coherence length of light source. A metallic object, covered by a 150-microm-thick onion cell, is imaged with high resolution. Applications in ophthalmology are shown: structures of the anterior eye, the cornea, and the iris, are studied on enucleated porcine eyes. Tomographic images of the iris border close to the pupil were obtained 165 microm underneath the eye surface.

Coherent anti-stokes Raman scattering imaging of axonal myelin in live spinal tissues.

We present a vibrational imaging study of axonal myelin under physiological conditions by laser-scanning coherent anti-Stokes Raman scattering (CARS) microscopy. We use spinal cord white matter strips that are isolated from guinea pigs and kept alive in oxygen bubbled Krebs' solution. Both forward- and epi-detected CARS are used to probe the parallel axons in the spinal tissue with a high vibrational contrast. With the CARS signal from CH2 vibration, we have measured the ordering degree and the spectral profile of myelin lipids. Via comparison with the ordering degrees of lipids in myelin figures formed of controlled lipid composition, we show that the majority of the myelin membrane is in the liquid ordered phase. By measuring the myelin thickness and axon diameter, the value of g ratio is determined to be 0.68 with forward- and 0.63 with epi-detected CARS. Detailed structures of the node of Ranvier and Schmidt-Lanterman incisure are resolved. We have also visualized the ordering of water molecules between adjacent bilayers inside the myelin. Our observations provide new insights into myelin organization, complementary to the knowledge from light and electron microscopy studies of fixed and dehydrated tissues. In addition, we have demonstrated simultaneous CARS imaging of myelin and two-photon excitation fluorescence imaging of intra- and extraaxonal Ca2+. The current work opens up a new approach to the study of spinal cord injury and demyelinating diseases.