OCT Technology Research Articles

OCT Biometry (B-OCT): A New Method for Measuring Ocular Axial Dimensions.

Purpose To present a new method of measuring ocular axial dimensions, termed OCT biometry (B-OCT). Design Observational cross-sectional study and evaluation of new diagnostic technology. Methods B-OCT was implemented in the spectral domain OCT device for posterior and anterior segment imaging (REVO NX, Optopol Technology). A total of 349 eyes (214 of healthy subjects, 115 of patients with cataract, and 20 with severe macular diseases) were enrolled in the study. The results of B-OCT were compared to swept source OCT-based IOLMaster 700 (Carl Zeiss Meditec). Differences in measurement values between the two biometers were determined using the paired t-test. Agreement was assessed through intraclass correlation coefficients (ICCs) and Bland–Altman plots. Results B-OCT obtained with REVO NX provides excellent interobserver reproducibility (ICC for: axial length (AXL) = 1.000; central corneal thickness (CCT) = 0.933; anterior chamber depth (ACD) = 0.933; lens thickness (LT) = 0.985) and intraobserver repeatability (ICC for: AXL = 1.000; CCT ≥ 0.994; ACD = 0.998; LT ≥ 0.993). The correlation between measurements made using both devices was outstanding (ICC for: AXL, healthy = 1.000; AXL, cataractous = 1.000; ACD, healthy = 0.998; ACD, cataractous = 0.997; LT, healthy = 0.998; LT, cataractous = 0.997; CCT, healthy = 0.989; CCT, cataractous = 0.979). The mean AXL measurement difference in healthy eyes was −0.001 ± 0.016 mm (the 95% LoA ranged from −0.034 to 0.031); mean ACD difference was 0.000 ± 0.024 mm (95% LoA, −0.047 to 0.047); mean LT difference was −0.002 ± 0.024 mm (95% LoA, −0.050 to 0.046); and mean CCT difference was −0.8 ± 5.1 μm (95% LoA, −10.81 to 9.26). The mean AXL measurement difference in cataractous eyes was −0.003 ± 0.022 mm (95% LoA, −0.046 to 0.039); mean ACD difference was 0.003 ± 0.029 mm (95% LoA, −0.054 to 0.059); mean LT difference was −0.002 ± 0.025 (95% LoA, −0.051 to 0.048); and mean CCT difference was 2.7 ± 6.4 μm (95% LoA, −9.80 to 15.7). Conclusion The study shows small, nonsignificant differences between the biometric measurements obtained with REVO NX B-OCT and IOLMaster 700, which is of high significance for IOL power selection. As B-OCT utilizes a conventional OCT device, the measurements of the ocular axial dimensions are combined with high-resolution macular scans for the simultaneous assessment of central retina as a part of screening for macular pathology. The presented method is the first spectral domain OCT-based biometry technique and the only one integrated into a standard OCT device. Thus, it brings novel functionality to OCT technology.

Full-range Fourier-domain optical coherence tomography based on Mach–Zehnder interferometer

We proposed a full-range Fourier-domain optical coherence tomography (FR-FDOCT) based on a Mach–Zehnder interferometer with a tilted mirror which could generate a series of accurate phase-delay interference signals simultaneously. The FR-FDOCT is capable of acquiring artifact-free images by the construction of both amplitude and phase of the interferogram from multiple sets of phase-delay signals. The Mach–Zehnder interferometer make the reference arm became single-way optical path which is more convenient to adjust the reference beam than the return-way optical path (which means the incident and reflected beams use the same optical path) of traditional systems. A series of phase-delay interference signals were simultaneously acquired by a home-made two-dimensional spectrometer when tilting the mirror in the reference arm. The technique was employed to measure an anterior chamber of a porcine eye with a high symmetric artifact suppression of more than 45 dB. The technology could achieve double-range images effectively without any additional scanning device. It could actively promote the innovation and development of OCT technology.

Anterior Segment Optical Coherence Tomography: Applications for Clinical Care and Scientific Research.

Anterior segment optical coherence tomography (AS-OCT) is a non-contact imaging technique that produces high-resolution images and quantitative measurements of the anterior segment and its anatomical structures. There has been rapid development of OCT technology over the past 2 decades, with the transition from time-domain to Fourier-domain OCT devices. By integrating these advancements in OCT technology, AS-OCT devices have evolved into versatile clinical and research tools for studies of the anterior segment and ocular surface. The primary purpose of this article was to review OCT technology and AS-OCT devices as well as applications of AS-OCT for clinical practice and scientific research. We first describe the different types of OCT technology, how they have been adapted for AS-OCT imaging, and differences between various AS-OCT devices. We then review the applications of AS-OCT for characterizing the anatomical structures of the anterior segment and aqueous outflow pathways, including the anterior chamber angle, trabecular meshwork, and Schlemm canal. We also describe glaucoma-related applications of AS-OCT imaging, which include evaluating patients for static and dynamic biometric risk factors of primary angle closure disease and assessing the efficacy of glaucoma interventions, such as laser peripheral iridotomy and glaucoma surgery. Finally, we review other clinical applications of AS-OCT imaging for detection and management of diseases of the ocular surface, cornea, and lens.

In Vivo Vibration Measurement of Middle Ear Structure Using Doppler Optical Coherence Tomography: Preliminary Study.

Objectives Doppler optical coherence tomography (DOCT) is useful for both, the spatially resolved measurement of the tympanic membrane (TM) oscillation and high-resolution imaging. We demonstrated a new technique capable of providing real-time two-dimensional Doppler OCT image of rapidly oscillatory latex mini-drum and in vivo rat TM and ossicles.Methods Using DOCT system, the oscillation of sample was measured at frequency range of 1–4 kHz at an output of 15 W. After the sensitivity of the DOCT system was verified using a latex mini-drum consisting of a 100 μm-thick latex membrane, changes in displacement of the umbo and contacted area between TM and malleus in normal and pathologic conditions.Results The oscillation cycles of the mini-drum for stimulus frequencies were 1.006 kHz for 1 kHz, 2.012 kHz for 2kHz, and 3.912 kHz for 4 kHz, which means that the oscillation cycle of the mini-drum become short in proportional to the frequency of stimuli. The oscillation cycles of umbo area and the junction area in normal TM for frequencies of the stimuli showed similar integer ratio with the data of latex mini-drum for stimuli less than 4 kHz. In the case of middle ear effusion condition, the Doppler signal showed a tendency of attenuation in all frequencies, which was prominent at 1 kHz and 2 kHz.Conclusion The TM vibration under sound stimulation with frequencies from 1 kHz to 4 kHz in normal and pathologic conditions was demonstrated using signal demodulation method in in vivo condition. The OCT technology could be helpful for functional and structural assessment as an optional modality.

Distinguishing Highly Asymmetric Keratoconus Eyes Using Combined Scheimpflug and Spectral-Domain OCT Analysis

To determine optimal objective, machine-derived variables and variable combinations from Scheimpflug and spectral-domain (SD) OCT imaging to distinguish the clinically unaffected eye in patients with asymmetric keratoconus (AKC) from a normal control population. Retrospective case-control study. Thirty clinically unaffected eyes with no physical findings on slit-lamp examination, no definitive abnormalities on corneal imaging, and corrected distance acuity of 20/20 or better from 30 patients with highly AKC eyes and 60 eyes from 60 normal control patients who had undergone uneventful LASIK with at least 2 years of stable follow-up (controls). Scheimpflug and SD OCT imaging were obtained in all eyes, and receiver operating characteristic (ROC) curves were generated to determine area under the curve (AUC), sensitivity, and specificity for each machine-derived variable and variable combination. Distinguishing AKC eyes from controls as determined by AUC, sensitivity, and specificity. No individual machine-derived metric from Scheimpflug or SD OCT technology yielded an AUC higher than 0.75. Combining 5 Scheimpflug metrics (index height decentration [IHD], index vertical asymmetry [IVA], pachymetry apex, inferior-superior value, and Ambrosio's Relational Thickness Maximum [ARTmax]) yielded the best Scheimpflug results (AUC 0.86, sensitivity 83%, specificity 83%). Combining 11 SD OCT thickness metrics (minimum-median, temporal outer, superior nasal outer, minimum, epithelium minimum-maximum, epithelial standard deviation, superior inner, superior outer, superior temporal outer, superior nasal inner, central) yielded the best SD OCT results (AUC 0.96, sensitivity 89%, specificity 89%). Combining 13 total Scheimpflug/SD OCT metrics yielded the best results overall (AUC 1.0, sensitivity 100%, specificity 100%). The most impactful variables in combined models included epithelial thickness variability and total focal corneal thickness variability from SD OCT and anterior curvature and topometric indices from Scheimpflug technology. No posterior corneal metrics were impactful in modeling. Individual machine-derived metrics from Scheimpflug and SD OCT imaging poorly distinguished normal eyes from minimally affected eyes from patients with highly AKC. Combined SD OCT metrics performed better than combined Scheimpflug metrics. Combining anterior curvature and asymmetry indices from Scheimpflug with regional total thickness and epithelial thickness variability metrics from SD OCT clearly distinguished the 2 populations. Posterior corneal indices were not useful in distinguishing populations.

Retinal and optic nerve degeneration in \u03b1-mannosidosis

Backgroundα-mannosidosis is a rare, autosomal-recessive, lysosomal storage disease caused by a deficient activity of α-mannosidase. Typical symptoms include intellectual, motor and hearing impairment, facial coarsening, and musculoskeletal abnormalities. Ocular pathologies reported previously were mainly opacities of the cornea and lens, strabismus, and ocular motility disorders. However, retinal and optic nerve degeneration have been rarely described.MethodsWe report ocular findings of 32 patients with α-mannosidosis. We particularly concentrated on retinal abnormalities which we supported by posterior segment examination, fundus photography, and Spectral-Domain optical coherence tomography (SD-OCT) imaging.ResultsTapeto-retinal degeneration with bone spicule formations in the peripheral retina or macular changes were seen in three patients (9.4%) on funduscopy; of these, two with optic nerve atrophy. Eight retinal images could be obtained by OCT or fundus photography; of these, six showed thinning of the outer retinal layers on OCT. Overall, optic nerve atrophy was seen in six patients (18.8%); of these, four with partial atrophy. Two patients had partial optic nerve atrophy with no retinal abnormalities on funduscopy. Cataract was seen in two (6.3%), corneal haze also in two patients (6.3%). Six patients (18.8%) had manifest strabismus, four (12.5%) nystagmus, and in five patients (15.6%) impaired smooth pursuit eye movements were seen.ConclusionOcular pathologies are not exclusively confined to opacities of the cornea and lens or strabismus and ocular motility disorders but tapeto-retinal degeneration and optic nerve atrophy may be a common feature in α-mannosidosis. OCT technology helps detecting early outer retinal thinning which can progress with age and potentially leads to vision loss over time.

OCT and retinal ganglion cell layer

SummaryVision is highly dependent on both retinal ganglion cells (RGC) and their axons. Vision salvation depends on the prevention of RGC loss, and the time window to initiate a neuroprotective therapy after injury is not well defined in humans.Recent developments in both OCT technology and software have allowed a precise and reproducible assessment of the RGC layer to be possible in vivo in humans. The goals of this presentation are two‐fold : first, to review the mechanisms of both axonal and RGC degeneration; second, to discuss the time‐course of RGC loss after either antechiasmal or retrogeniculate lesions.At the end of the talk, participants should understand the mechanisms and time‐course of RGC and axonal loss.

Advances of OCT Technology for Laser Beam Processing

AbstractOptical coherence tomography (OCT) is an innovative sensor 3D measuring system for automated laser processing, in particular laser welding. It facilitates laser beam positioning, process monitoring, and quality control with the required precision and guarantees process flexibility, stability, and trace‐ability. To ensure smooth seam tracking for time‐ and cost‐effective line production, Lessmüller Lasertechnik OCT systems offer the automated recognition and digitalization of joints for precise lateral and axial positioning. It provides industrial solutions for the online inspection of the keyhole to enable consistent and high quality welds.

Optical coherence tomography angiography: A comprehensive review of current methods and clinical applications.

OCT has revolutionized the practice of ophthalmology over the past 10-20 years. Advances in OCT technology have allowed for the creation of novel OCT-based methods. OCT-Angiography (OCTA) is one such method that has rapidly gained clinical acceptance since it was approved by the FDA in late 2016. OCTA images are based on the variable backscattering of light from the vascular and neurosensory tissue in the retina. Since the intensity and phase of backscattered light from retinal tissue varies based on the intrinsic movement of the tissue (e.g. red blood cells are moving, but neurosensory tissue is static), OCTA images are essentially motion-contrast images. This motion-contrast imaging provides reliable, high resolution, and non-invasive images of the retinal vasculature in an efficient manner. In many cases, these images are approaching histology level resolution. This unprecedented resolution coupled with the simple, fast and non-invasive imaging platform have allowed a host of basic and clinical research applications. OCTA demonstrates many important clinical findings including areas of macular telangiectasia, impaired perfusion, microaneurysms, capillary remodeling, some types of intraretinal fluid, and neovascularization among many others. More importantly, OCTA provides depth-resolved information that has never before been available. Correspondingly, OCTA has been used to evaluate a spectrum of retinal vascular diseases including diabetic retinopathy (DR), retinal venous occlusion (RVO), uveitis, retinal arterial occlusion, and age-related macular degeneration among others. In this review, we will discuss the methods used to create OCTA images, the practical applications of OCTA in light of invasive dye-imaging studies (e.g. fluorescein angiography) and review clinical studies demonstrating the utility of OCTA for research and clinical practice.

A brief history of OCT

Since its ophthalmic application was identified, OCT technology has advanced in leaps and bounds. Lewis Williams provides a brief overview of the technology's origins and evolution.

Optical coherence elastography - OCT at work in tissue biomechanics [Invited

Optical coherence elastography (OCE), as the use of OCT to perform elastography has come to be known, began in 1998, around ten years after the rest of the field of elastography - the use of imaging to deduce mechanical properties of tissues. After a slow start, the maturation of OCT technology in the early to mid 2000s has underpinned a recent acceleration in the field. With more than 20 papers published in 2015, and more than 25 in 2016, OCE is growing fast, but still small compared to the companion fields of cell mechanics research methods, and medical elastography. In this review, we describe the early developments in OCE, and the factors that led to the current acceleration. Much of our attention is on the key recent advances, with a strong emphasis on future prospects, which are exceptionally bright.

The Edge Detectors Suitable for Retinal OCT Image Segmentation

Retinal layer thickness measurement offers important information for reliable diagnosis of retinal diseases and for the evaluation of disease development and medical treatment responses. This task critically depends on the accurate edge detection of the retinal layers in OCT images. Here, we intended to search for the most suitable edge detectors for the retinal OCT image segmentation task. The three most promising edge detection algorithms were identified in the related literature: Canny edge detector, the two-pass method, and the EdgeFlow technique. The quantitative evaluation results show that the two-pass method outperforms consistently the Canny detector and the EdgeFlow technique in delineating the retinal layer boundaries in the OCT images. In addition, the mean localization deviation metrics show that the two-pass method caused the smallest edge shifting problem. These findings suggest that the two-pass method is the best among the three algorithms for detecting retinal layer boundaries. The overall better performance of Canny and two-pass methods over EdgeFlow technique implies that the OCT images contain more intensity gradient information than texture changes along the retinal layer boundaries. The results will guide our future efforts in the quantitative analysis of retinal OCT images for the effective use of OCT technologies in the field of ophthalmology.

Introduction to ultrahigh‐resolution OCT

SummaryVarious diseases can have significant effects on morphological and functional aspects of the anterior segment of the eye. These may include alterations in corneal anatomy, i.e. changes in thickness of epithelium and Bowman's layer, structural changes in the anterior chamber and aqueous outflow system or alterations in tear film thickness and tear secretion.Optical coherence tomography (OCT) is a non‐invasive optical imaging modality enabling cross‐sectional in vivo imaging of internal microstructure in biological tissues. However, commercially available OCT technology sometimes does not provide sufficient resolution for in vivo visualization of the fine anatomy of the anterior eye segment. In this talk, an ultrahigh‐resolution OCT system that is based on a Titanium:Sapphire laser and provides an axial resolution below 2 μm is introduced. It allows in vivo imaging the anatomy of the cornea, limbal and scleral region as well as the structure of the lens with unprecedented richness of detail and resolution. Furthermore, the precorneal tear film can be visualized.The technology might have considerable potential for both the diagnosis and the investigation of surgical outcome in various ocular diseases.

From time domain to high resolution and angio‐OCT: an historical perspective

SummaryOptical coherence tomography (OCT) is a non‐invasive tool that allows in vivo imaging of almost all the structures of the eye. It was introduced into the clinical practice more than twenty years ago. The advances in OCT technology are mainly based on ultra high‐resolution, adaptive optics, eye‐tracking, and changes in signal detection. Regarding this last aspect, the technology has evolved from time‐domain (TD) to spectral‐domain (SD) detection, providing a higher definition of the analyzed structures. Today, SD OCT has become a part of the routine practice. Apart from its diagnostic value, OCT has allowed an objective assessment of treatment response. In addition, it has provided predictive value for visual recovery and prognosis of several diseases. Recently, SD‐OCT has given to the ophthalmic researchers a renewed enthusiasm: a special processing algorithm has been developed for high‐speed OCT devices. This OCT technique, known as OCT angiography, can produce images of capillary‐level blood flow in the retina and choroid. OCT technology continues to develop further and this will provide new insights for the pathogenesis of several eye diseases.

OCT imaging in glaucoma and PEX

SummaryGlaucoma, as one of the leading causes of blindness worldwide, can be characterized by abnormalities in the aqueous outflow system (AOS) structures, including Schlemm's canal, that regulate the IOP in a healthy eye. Furthermore, the accumulation of pseudoexfoliation (PEX) deposits in the anterior chamber can increase the risk of the disease. The imaging of the anterior eye segment and here in particular the limbal area and anterior lens capsule could have a special clinical significance, since there is an evidence that symptomatic PEX is preceded by subclinical ultrastructural changes in the anterior segment including the lens surface.In this course, ultrahigh‐resolution optical coherence tomography for imaging of the anterior eye segment in glaucoma and PEX patients will be introduced. The advantage of the superior resolution as compared to commercially available OCT technology for visualization of AOS structures and PEX deposits on the lens capsule as well as its potential for evaluation of Schlemm's canal diameter will be shown and possible applications of the technology in clinical practice will be discussed.

Wide-field optical coherence tomography based microangiography for retinal imaging.

Optical coherence tomography angiography (OCTA) allows for the evaluation of functional retinal vascular networks without a need for contrast dyes. For sophisticated monitoring and diagnosis of retinal diseases, OCTA capable of providing wide-field and high definition images of retinal vasculature in a single image is desirable. We report OCTA with motion tracking through an auxiliary real-time line scan ophthalmoscope that is clinically feasible to image functional retinal vasculature in patients, with a coverage of more than 60 degrees of retina while still maintaining high definition and resolution. We demonstrate six illustrative cases with unprecedented details of vascular involvement in retinal diseases. In each case, OCTA yields images of the normal and diseased microvasculature at all levels of the retina, with higher resolution than observed with fluorescein angiography. Wide-field OCTA technology will be an important next step in augmenting the utility of OCT technology in clinical practice.

Reducing stroke damage: Next application for OCT technology?

Reducing stroke damage: Next application for OCT technology?

OCT Angiography - Is this the Future for Macular Diagnosis?

Recent developements in OCT technology using high speed acquisition and calculation of consecutive scans (SSADA = split spectrum amplitude decorrelation algorithm) have resulted in the possibility to demonstrate retinal and choroidal vessels in the macula. This new technology of "OCT angiography" thus allows the non-invasive and rapid (within seconds) reconstruction of the three-dimensional structure of the retinal and choroidal vascularisation. There are still limitations caused by movement artefacts, superposition of superficial retinal vessels at the RPE level or insufficient three-dimensional imaging, but the first experience with this new method and especially the correlations with the current standard diagnostic procedure fluorescein angiography shows that especially for vascular changes which are predominantly in one retinal layer (e.g., the inner retina) like in diabetic retinopathy or retinal vein occlusions, a very good correlation can be seen. Also in MacTel type 2 patients the proposed vascular changes in the deeper capillary network of the retina can be visualised very well with OCT angiography. In contrast, more three-dimensional vascular changes like the neovascular complex in exsudative AMD need a more sophisticated diagnostic analysis strategy, which has still to be developed. However, the first experience also demonstrates that fluorescein angiographic differentiation can also be seen in OCT angiography. In addition, the new technology gives additional information about the choroidal and outer retinal changes in these pathologies, which may result in a better understanding of the underlying pathologies.

Ultra-widefield retinal MHz-OCT imaging with up to 100 degrees viewing angle.

We evaluate strategies to maximize the field of view (FOV) of in vivo retinal OCT imaging of human eyes. Three imaging modes are tested: Single volume imaging with 85° FOV as well as with 100° and stitching of five 60° images to a 100° mosaic (measured from the nodal point). We employ a MHz-OCT system based on a 1060nm Fourier domain mode locked (FDML) laser with a depth scan rate of 1.68MHz. The high speed is essential for dense isotropic sampling of the large areas. Challenges caused by the wide FOV are discussed and solutions to most issues are presented. Detailed information on the design and characterization of our sample arm optics is given. We investigate the origin of an angle dependent signal fall-off which we observe towards larger imaging angles. It is present in our 85° and 100° single volume images, but not in the mosaic. Our results suggest that 100° FOV OCT is possible with current swept source OCT technology.

Material Defects in Ceramic Crowns Identification by Optical Coherence Tomography and MicroCT

Full ceramic crowns are considered revolutionary in developing the concept of aesthetic dentistry. Appreciate their aesthetic appearance particularly raise the cost prices, they do not ensure the risk of fractures and cracks which sometimes face the clinician after their insertion directly into the mouth. As a result of the fracture may occur between disputes team dentist-dental technician. The purpose of this study was to identify flaws of material included in the pottery table analyzing the full ceramic crowns using non-invasive technologies. As materials we use 25 full ceramic crowns (e. max, IVOCLAR) obtained through the technology of pressing were used for this study. Non-invasive methods used for this study were OCT and Micro CT. The OCT technology works in Time Domain, at 1300 nm and scan angle at 18 degrees, and for each sample scans were carried out in areas of maximum voltage. After the scans, we have been obtained through the stack of 500 slicers at a distance of 10 microns each other. A number of 17 samples of the total samples obtained exhibited defects in areas of major stress corresponding to the crown considered. As a result of defects discovered using the technology OCT it has considered necessary for validation them by employing the Micro CT technology. In conclusion, we consider that OCT technology can be considered an early diagnosis method of faults contained in the table structure of the ceramic crowns before inserting them in the oral cavity, by reducing the risks of a prosthetic treatment.