En-face Optical Coherence Tomography Images Research Articles

Evaluating glaucomatous abnormality in peripapillary optical coherence tomography enface visualisation of the retinal nerve fibre layer reflectance.

PurposeOptical coherence tomography (OCT) enface visualisation of the retinal nerve fibre layer (RNFL) reflectance has been found to have some advantages over retinal thickness measures. However, it is not yet clear how abnormalities on enface images relate to findings of abnormalities from other clinical measures such as the circumpapillary retinal nerve fibre layer thickness (cRNFLT). We developed a technique to analyse the RNFL reflectance on the OCT enface images, and to investigate its relation with the cRNFLT.MethodsSpectralis (http://www.heidelbergengineering.com) OCT scans of the central retinal ±24° were analysed in the study eye of 31 controls and 33 patients, ages 61 (±9) and 69 (±8) years respectively. Enface slab‐images were extracted at 16–24, 24–36, and 24–52 μm from the inner limiting membrane in the temporal raphe, perifoveal and disc regions respectively. Reflectance probability maps were generated for the patients based on the control data. Glaucomatous abnormality was defined on the slab‐images when the slab‐area with reflectance abnormality was greater than the 95th percentile, and on the cRNFLT when the thickness measure was less than the fifth percentile, of that found in controls. The fraction of slab‐image showing reflectance abnormality was compared to cRNFLT in the patient group, using Spearman's rho. Agreement between the findings of abnormality based on cRNFLT and slab‐image reflectance was assessed using Cohen's kappa.ResultsSlab‐image and cRNFLT findings were in agreement for 26/33 eyes; four subjects showed cRNFLT abnormality but not slab‐image abnormality, and three subjects showed slab‐image abnormality but not cRNFLT abnormality. Spearman's rho found r s(31) = −0.82. The reflectance findings and cRNFLT findings were consistent in 27/33 for both the superior temporal (ST) and inferior temporal (IT) sectors, and Cohen's kappa found 0.53 and 0.61 respectively.ConclusionThe surface area of enface slab‐images showing RNFL reflectance were strongly related to the cRNFLT measures, and the classification of a subject with glaucoma based on enface reflectance findings and cRNFLT findings had a generally good agreement. The larger retinal area assessed by the enface method preserves the spatial location of the RNFL abnormalities, and makes the technique a useful approach for identifying regions of potential RNFL abnormality for targeted perimetry.

Torpedo Maculopathy Presenting With Fovea Plana in a 21-Year-Old Female

Purpose: To report a case of torpedo maculopathy presenting with fovea plana in a 21-year-old female patient. Methods: Multimodal imaging including fluorescein angiography, fundus autofluorescence, and spectral domain optical coherence tomography (OCT) was used to characterize pathology. Results: A well-circumscribed ellipsoidal hypopigmented lesion was observed inferotemporal to the fovea OS. Fluorescein angiography and fundus autofluorescence revealed hyperfluorescence and focal hypoautofluorescence, respectively, corresponding to the hypopigmented lesion. Spectral domain optical coherence tomography imaging of the lesion revealed attenuation of the ellipsoid zone and retinal pigment epithelium with a hyporeflective subretinal cleft. En face OCT imaging demonstrated an area of subretinal hyporeflectivity at the subretinal cleft. Spectral domain optical coherence tomography revealed the absence of a foveal pit. Conclusion: We have described a novel case presentation of fovea plana alongside torpedo maculopathy. The significance of this association remains unclear. Further study into these conditions is necessary to help better determine factors responsible for visual symptoms or lack thereof and circumstances that promote their development.

Effects of Temperature Variations during Sintering of Metal Ceramic Tooth Prostheses Investigated Non-Destructively with Optical Coherence Tomography

Calibration loss of ovens used in sintering metal ceramic prostheses leads to stress and cracks in the material of the prostheses fabricated, and ultimately to failure of the dental treatment. Periodic calibration may not be sufficient to prevent such consequences. Evaluation methods based on firing supplemental control samples are subjective, time-consuming, and rely entirely on the technician’s skills. The aim of this study was to propose an alternative procedure for such evaluations. Fifty prostheses were sintered in a ceramic oven at a temperature lower, equal to or larger than the temperature prescribed by the manufacturer. A non-destructive imaging method, swept source (SS) optical coherence tomography (OCT) was used to evaluate comparatively the internal structure of prostheses so fabricated. A quantitative assessment procedure is proposed, based on en-face OCT images acquired at similar depths inside the samples. Differences in granulation and reflectivity depending on the oven temperature are used to establish rules-of-thumb on judging the correct calibration of the oven. OCT evaluations made on a regular basis allow an easy and objective monitoring of correct settings in the sintering process. This method can serve rapid identification of the need to recalibrate the oven and avoid producing prostheses with defects.

Enhanced Visualization of Subtle Outer Retinal Pathology by En Face Optical Coherence Tomography and Correlation with Multi-Modal Imaging.

PurposeTo present en face optical coherence tomography (OCT) images generated by graph-search theory algorithm-based custom software and examine correlation with other imaging modalities.MethodsEn face OCT images derived from high density OCT volumetric scans of 3 healthy subjects and 4 patients using a custom algorithm (graph-search theory) and commercial software (Heidelberg Eye Explorer software (Heidelberg Engineering)) were compared and correlated with near infrared reflectance, fundus autofluorescence, adaptive optics flood-illumination ophthalmoscopy (AO-FIO) and microperimetry.ResultsCommercial software was unable to generate accurate en face OCT images in eyes with retinal pigment epithelium (RPE) pathology due to segmentation error at the level of Bruch’s membrane (BM). Accurate segmentation of the basal RPE and BM was achieved using custom software. The en face OCT images from eyes with isolated interdigitation or ellipsoid zone pathology were of similar quality between custom software and Heidelberg Eye Explorer software in the absence of any other significant outer retinal pathology. En face OCT images demonstrated angioid streaks, lesions of acute macular neuroretinopathy, hydroxychloroquine toxicity and Bietti crystalline deposits that correlated with other imaging modalities.ConclusionsGraph-search theory algorithm helps to overcome the limitations of outer retinal segmentation inaccuracies in commercial software. En face OCT images can provide detailed topography of the reflectivity within a specific layer of the retina which correlates with other forms of fundus imaging. Our results highlight the need for standardization of image reflectivity to facilitate quantification of en face OCT images and longitudinal analysis.

Different foveal schisis patterns in each retinal layer in eyes with hereditary juvenile retinoschisis evaluated by en-face optical coherence tomography.

To analyze the structures of schisis in eyes with hereditary juvenile retinoschisis using en-face optical coherence tomography (OCT) imaging. In this retrospective observational study, we reviewed the medical records of patients with hereditary juvenile retinoschisis who underwent comprehensive ophthalmic examinations including swept-source OCT. OCT images were obtained from 16 eyes of nine boys (mean age ± standard deviation, 10.6 ± 4.0years). The horizontal OCT images at the fovea showed inner nuclear layer (INL) schisis in one eye (6.3%), ganglion cell layer (GCL) and INL schisis in 12 eyes (75.0%), INL and outer plexiform layer (OPL) schisis in two eyes (12.5%), and GCL, INL, and OPL schisis in one eye (6.3%). En-face OCT images showed characteristic schisis patterns in each retinal layer, which were represented by multiple hyporeflective holes in the parafoveal region in the GCL, a spoke-like pattern in the foveal region, a reticular pattern in the parafoveal region in the INL, and multiple hyporeflective polygonal cavities with partitions in the OPL. Our results using en-face OCT imaging clarified different patterns of schisis formation among the GCL, INL, and OPL, which lead to further recognition of structure in hereditary juvenile retinoschisis.

En Face Optical Coherence Tomography Imaging for the Detection of Nascent Geographic Atrophy

To determine if en face optical coherence tomography (OCT) imaging can identify nascent geographic atrophy (nGA) in eyes with intermediate age-related macular degeneration (iAMD). Retrospective observational case series. Patients with iAMD from the COMPLETE study at the Bascom Palmer Eye Institute were evaluated to determine if nGA was present at baseline and at follow-up using high-density Spectralis OCT B-scans and en face OCT images from the Cirrus OCT instrument. If available, additional en face OCT images and B-scans were analyzed at follow-up times beyond the 52-week period. A total of 37 eyes (27 patients) were evaluated for at least 1 year using both B-scans and en face images. Two drusen suspicious for nGA at baseline were identified, but neither druse developed GA after 24 and 62months of follow-up, respectively. Another druse displayed hypertransmission into the choroid at week 52 on B-scan imaging and was classified as nGA. En face OCT imaging identified this druse as a focal bright area. Drusen breakdown occurred during a follow-up of 39months. En face OCT imaging appeared to be as useful as routine B-scan imaging for identifying areas suspicious for nGA in this population from the COMPLETE Study. Additional longitudinal follow-up of eyes with drusen is needed to determine if en face OCT imaging can replace the evaluation of individual B-scans for the detection of nGA.

Investigation of the Etiology of Central Serous Chorioretinopathy Using En-Face Optical Coherence Tomography and Indocyanine Green Angiography

Purpose: To identify locations of hypofluorescent lesions on late-phase indocyanine green angiography (ICGA) in patients with central serous chorioretinopathy (CSC) using en-face optical coherence tomography (OCT). Procedures: We retrospectively studied 25 consecutive untreated CSC patients, using swept-source OCT and ICGA. En-face swept-source OCT images were automatically segmented and flattened with Bruch's membrane (BrM). We compared the sizes of hyperreflective areas in the 25 CSC and 25 contralateral eyes on en-face images and hypofluorescent areas on ICGA after 30 min. Results: All 25 CSC eyes and 13 contralateral eyes showed abnormal hypofluorescent areas on late-phase ICGA and hyperreflective areas on en-face OCT from BrM to the choriocapillaris, and these findings correlated with the abnormal areas (r = 0.9988; p < 0.001). Conclusions: In CSC patients, we detected abnormal hypofluorescence on ICGA in the late phase, which corresponded to abnormal hyperreflective areas from BrM to the choriocapillaris level in en-face images.

Circumferential optical coherence tomography angiography imaging of the swine esophagus using a micromotor balloon catheter.

We demonstrate a micromotor balloon imaging catheter for ultrahigh speed endoscopic optical coherence tomography (OCT) which provides wide area, circumferential structural and angiographic imaging of the esophagus without contrast agents. Using a 1310 nm MEMS tunable wavelength swept VCSEL light source, the system has a 1.2 MHz A-scan rate and ~8.5 µm axial resolution in tissue. The micromotor balloon catheter enables circumferential imaging of the esophagus at 240 frames per second (fps) with a ~30 µm (FWHM) spot size. Volumetric imaging is achieved by proximal pullback of the micromotor assembly within the balloon at 1.5 mm/sec. Volumetric data consisting of 4200 circumferential images of 5,000 A-scans each over a 2.6 cm length, covering a ~13 cm(2) area is acquired in <18 seconds. A non-rigid image registration algorithm is used to suppress motion artifacts from non-uniform rotational distortion (NURD), cardiac motion or respiration. En face OCT images at various depths can be generated. OCT angiography (OCTA) is computed using intensity decorrelation between sequential pairs of circumferential scans and enables three-dimensional visualization of vasculature. Wide area volumetric OCT and OCTA imaging of the swine esophagus in vivo is demonstrated.

Evaluation of Blebs After Filtering Surgery With En-Face Anterior-Segment Optical Coherence Tomography: A Pilot Study.

To compare characteristics of functioning blebs (FBs) and nonfunctioning blebs (NFBs) with en-face spectral-domain optical coherence tomography (OCT). We evaluated 41 blebs of 38 patients after a first-time trabeculectomy. Eyes were classified into 2 groups: FBs (22 eyes) and NFBs (19 eyes). En-face OCT images were analyzed semiquantitatively for the density of intraepithelial microcysts (0 to 3), internal fluid-filled cavity (0 to 3), and bleb vascularization (0 to 2). Presence of conjunctival fibrosis and visualization of the scleral flap were also analyzed. FBs showed significantly more intraepithelial microcysts than did NFBs: the mean grading of microcyst density was 1.86 for FBs and 0.11 for NFBs (P<0.0001). None of the FBs were rated 0 and none of the NFBs were rated 2 or 3 for the density of intraepithelial microcysts. NFBs presented more conjunctival fibrosis than FBs (63% vs. 32%, P<0.05). There was no significant difference between FBs and NFBs for bleb vascularization, visualization of the scleral flap, and presence of subepithelial fluid-filled cavities. There was a direct correlation between postoperative intraocular pressure and intraepithelial microcyst density (r=-0.7655, P<0.0001). The long-term administration of preserved eyedrops before surgery was associated with fewer intraepithelial microcysts (r=-0.5436; P=0.0006). FBs were associated with a higher number of intraepithelial microcysts evaluated with en-face OCT. A higher density of microcysts was associated with a lower intraocular pressure and a shorter duration of preserved topical treatment before surgery. En-face OCT provides a simple, noninvasive, and reproducible method to analyze blebs after filtering surgery.

Application to skin physiology using optical coherence tomography.

Background and aims: The sweat glands and peripheral vessels beneath the skin surface act as minute organs governed by the skin sympathetic nerves and have important physiological functions for body temperature control and nutrition support along with maintenance of a peripheral organization. Dynamics of the mental sweating of sweat glands and the peripheral vessels reflect the activity of a sympathetic nerve. The purpose of this paper is to study the dynamic observation and analysis of sweat glands and a peripheral vessels by optical coherence tomography (OCT). Materials and Methods: In the dynamic analysis of mental sweating of sweat glands, after confirmation of the resting state of the volunteer, mental stress was applied in the form of unpleasant sound for 0.5 sec; piled-up en-face OCT images of sweat glands were then obtained time-sequentially, with the frame-spacing of 3.3 sec. A swept-source (SS) OCT was used for in vivo en-face OCT of a group of sweat glands on the subject's fingertip. Furthermore, we conducted in vivo dynamic analysis in response to external mental stress of a peripheral vessel in the second joint of the subject's third finger using 1.3-µm SS OCT. Results: We analyzed time variation in the amount of excess sweat produced by a group of sweat glands and found a large difference in the amount of sweat stored by each sweat gland in the spiral lumen. Mental stress was also shown to cause the small artery of the finger to contract, reducing blood flow. In particular, the thickness of the tunica media of the small artery changed abruptly in response to the sound stress, increasing and then decreasing so that the artery contracted and expanded, respectively. Conclusions: Dynamic analysis of mental sweating in the eccrine sweat glands and changes in peripheral vessels was performed using time-sequential OCT imaging. For mental sweating, time variation in the amount of excess sweat produced could be simultaneously evaluated for a few tens of eccrine sweat glands. Furthermore, we performed the dynamic analysis of a peripheral vessel in a human finger in response to external mental stress and found that the small artery contracted and expanded in response to sound stress while continuing to pulse in synchronization with the heartbeat. These studies have the potential for establishing new knowledge about skin physiology.

En Face Optical Coherence Tomography to Detect and Measure Geographic Atrophy.

To detect and quantify geographic atrophy (GA) secondary to age-related macular degeneration using en face optical coherence tomography (OCT) and to correlate it to GA measured with fundus autofluorescence (FAF). Twenty-four consecutive patients (27 eyes) were studied with both standard (STD)- and enhanced depth imaging (EDI)-OCT. En face OCT images were obtained at the outer retinal layer (OR) and at the choroidal layer (CH) level for both STD- and EDI-OCT. Areas of GA were measured on the en face OCT images and were correlated with the GA areas measured on blue (B)- and near infrared (NIR)-wavelength FAF images. The intraoperator agreement in GA measurement was excellent with en face OCT at both OR and CH levels (intraclass correlation coefficient [ICC] = 0.99 in EDI and 0.98 in STD at OR level; 0.99 in EDI and 0.99 in STD at CH level). The interoperator agreement was excellent at OR level (ICC = 0.97 in EDI and 0.98 in STD), good at CH level (ICC = 0.95 in EDI, 0.90 in STD). The geographic atrophy area, at both B-FAF and NIR-FAF, was significantly equivalent to the GA area at OR level (B-FAF versus SDT-OR and EDI-OR: P = 0.0057 and 0.0090, respectively; NIR-FAF versus STD-OR and EDI-OR: P = 0.0131 and 0.0036, respectively), but not at CH level. En face OCT is a reliable method to detect and quantify GA, particularly when analyzed at the OR level, where the photoreceptors' loss creates an abrupt transition in OCT reflectivity.

Semi-automated quantification of retinal IS/OS damage in en-face OCT image

A variety of vision ailments are indicated by structural changes in the retinal substructures of the posterior segment of the eye. In particular, integrity of the inner-segment/outer-segment (IS/OS) junction directly relates to the visual acuity. In the en-face optical coherence tomography (OCT) image, IS/OS damage manifests as a dark spot in the foveal region, and its quantification, usually performed by experts, assumes diagnostic significance. In this context, in view of the general scarcity of experts, it becomes imperative to develop algorithmic methods to reduce expert time and effort. Accordingly, we propose a semi-automated method based on level sets. As the energy function, we adopt mutual information which exploits the difference in statistical properties of the lesion and its surroundings. On a dataset of 27 en-face OCT images, segmentation obtained by the proposed algorithm exhibits close visual agreement with that obtained manually. Importantly, our results also match manual results in various statistical criteria. In particular, we achieve a mean Dice coefficient of 85.69%, desirably close to the corresponding observer repeatability index of 89.45%. Finally, we quantify algorithmic accuracy in terms of two quotient measures, defined relative to observer repeatability, which could be used as bases for comparison with future algorithms, even if the latter are tested on disparate datasets.

Adaptive optics SLO/OCT for 3D imaging of human photoreceptors in vivo

We present a new instrument that is capable of imaging human photoreceptors in three dimensions. To achieve high lateral resolution, the system incorporates an adaptive optics system. The high axial resolution is achieved through the implementation of optical coherence tomography (OCT). The instrument records simultaneously both, scanning laser ophthalmoscope (SLO) and OCT en-face images, with a pixel to pixel correspondence. The information provided by the SLO is used to correct for transverse eye motion in post-processing. In order to correct for axial eye motion, the instrument is equipped with a high speed axial eye tracker. In vivo images of foveal cones as well as images recorded at an eccentricity from the fovea showing cones and rods are presented.

Compact piezoelectric transducer fiber scanning probe for optical coherence tomography

We developed a compact, optical fiber scanning piezoelectric transducer (PZT) probe for endoscopic and minimally invasive optical coherence tomography (OCT). Compared with previous forward-mount fiber designs, we present a reverse-mount design that achieves a shorter rigid length. The fiber was mounted at the proximal end of a quadruple PZT tube and scanned inside the hollow PZT tube to reduce the probe length. The fiber resonant frequency was 338 Hz using a 17-mm-long fiber. A 0.9 mm fiber deflection was achieved with a driving amplitude of 35 V. Using a GRIN lens-based optical design with a 1.3× magnification, a ∼6 μm spot was scanned over a 1.2 mm diameter field. The probe was encased in a metal hypodermic tube with a ∼25 mm rigid length and covered with a 3.2 mm outer diameter (OD) plastic sheath. Imaging was performed with a swept source OCT system based on a Fourier domain modelocked laser (FDML) light source at a 240 kHz axial scan rate and 8 μm axial resolution (in air). En face OCT imaging of skin in vivo and human colon ex vivo was demonstrated.

Master–slave interferometry for parallel spectral domain interferometry sensing and versatile 3D optical coherence tomography

Conventional spectral domain interferometry (SDI) methods suffer from the need of data linearization. When applied to optical coherence tomography (OCT), conventional SDI methods are limited in their 3D capability, as they cannot deliver direct en-face cuts. Here we introduce a novel SDI method, which eliminates these disadvantages. We denote this method as Master - Slave Interferometry (MSI), because a signal is acquired by a slave interferometer for an optical path difference (OPD) value determined by a master interferometer. The MSI method radically changes the main building block of an SDI sensor and of a spectral domain OCT set-up. The serially provided signal in conventional technology is replaced by multiple signals, a signal for each OPD point in the object investigated. This opens novel avenues in parallel sensing and in parallelization of signal processing in 3D-OCT, with applications in high- resolution medical imaging and microscopy investigation of biosamples. Eliminating the need of linearization leads to lower cost OCT systems and opens potential avenues in increasing the speed of production of en-face OCT images in comparison with conventional SDI.

Simultaneous multiple-depths en-face optical coherence tomography using multiple signal excitation of acousto-optic deflectors

We present a novel low-coherence interferometer configuration, equipped with acousto-optic deflectors that can be used to simultaneously acquire up to eight time domain optical coherence tomography en-face images. The capabilities of the configuration are evaluated in terms of depth resolution, signal to noise ratio and crosstalk. Then the configuration is employed to demonstrate simultaneous en-face optical coherence tomography imaging at five different depths in a specimen of armadillidium vulgare.

Dynamic Analysis of Mental Sweating by the Time-Sequential Piled-Up En-Face OCT Images

In this paper, the dynamic analysis of mental sweating for sound stimulus of a few tens of eccrine sweat glands is performed by the time-sequential piled-up en-face optical coherence tomography (OCT) images with the frame spacing of 3.3 sec. In the experiment, the amount of excess sweat can be evaluated simultaneously for a few tens of sweat glands by piling up of all the en-face OCT images. Strong non-uniformity is observed in mental sweating where the amount of sweat in response to sound stimulus is different for each sweat gland. Furthermore, the amount of sweat is significantly increased in proportion to the strength of the stimulus.

En Face OCT Imaging for the Diagnosis of Outer Retinal Tubulations in Age-Related Macular Degeneration.

Purpose. “En face” is an emerging imaging technique derived from spectral domain optical coherence tomography (OCT). It produces frontal sections of retinal layers, also called “C-scan OCT.” Outer retinal tubulations (ORTs) in age-related macular degeneration (AMD) are a recent finding evidenced by spectral-domain OCT. The aim of this study is to characterize the morphology of ORT according to the form of AMD, using “en-face” spectral domain OCT. Methods. “En face” OCT imaging was prospectively performed in 26 consecutive eyes with AMD that also had ORT. Results. There were 15 neovascular, 8 atrophic, and 3 eyes with a mixed (fibrotic and atrophic) form of AMD. Among the neovascular group, the most frequent tubulation pattern on “en-face” OCT was a branching network emanating from a fibrovascular scar; we term this pattern as “pseudodendritic.” It did not require treatment when observed as an isolated finding. In all cases of atrophic AMD, the tubular network was located at the edge of the geographic atrophy area, and formed a “perilesional” pattern. Six atrophic cases showed tubular invaginations inside this area. Conclusion. “En face” OCT is a valuable technique in the diagnosis and followup of macular disease. It revealed the main characteristic patterns of ORT associated with neovascular and atrophic AMD.

Virtual four-dimensional imaging of lung parenchyma by optical coherence tomography in mice

In this feasibility study, we present a method for virtual 4-D imaging of healthy and injured subpleural lung tissue in the ventilated mouse. We use triggered swept source optical coherence tomography (OCT) with an A-scan frequency of 20 kHz to image murine subpleural alveoli during the inspiratory phase. The data acquisition is gated to the ventilation pressure to take single B-scans in each respiration cycle for different pressure levels. The acquired B-scans are combined off-line into one volume scan for each pressure level. The air fraction in healthy lungs and injured lungs is measured using 2-D OCT en-face images. Upon lung inspiration from 2 to 12 cm H(2)O ventilation pressure, the air fraction increases in healthy lungs by up to 11% and in injured lungs by 8%. This expansion correlates well with results of previous studies, reporting increased alveolar area with increased ventilation pressures. We demonstrate that OCT is a useful tool to investigate alveolar dynamics in spatial dimensions.

Co-registered optical coherence tomography and fluorescence molecular imaging for simultaneous morphological and molecular imaging

Optical coherence tomography (OCT) provides high-resolution, cross-sectional imaging of tissue microstructure in situ and in real time, while fluorescence molecular imaging (FMI) enables the visualization of basic molecular processes. There is a great deal of interest in combining these two modalities so that the tissue's structural and molecular information can be obtained simultaneously. This could greatly benefit biomedical applications such as detecting early diseases and monitoring therapeutic interventions. In this research, an optical system that combines OCT and FMI was developed. The system demonstrated that it could co-register en face OCT and FMI images with a 2.4 × 2.4 mm2 field-of-view. The transverse resolutions of OCT and FMI of the system are both ∼10 µm. Capillary tubes filled with fluorescent dye Cy 5.5 in different concentrations under a scattering medium are used as the phantom. En face OCT images of the phantoms were obtained and successfully co-registered with FMI images that were acquired simultaneously. A linear relationship between FMI intensity and dye concentration was observed. The relationship between FMI intensity and target fluorescence tube depth measured by OCT images was also observed and compared with theoretical modeling. This relationship could help in correcting reconstructed dye concentration. Imaging of colon polyps of the APCmin mouse model is presented as an example of biological applications of this co-registered OCT/FMI system.