Bio: J.C. Castro is an academic researcher from University of São Paulo. The author has contributed to research in topics: Phase conjugation & Wavefront. The author has an hindex of 11, co-authored 31 publications receiving 710 citations.
TL;DR: A brief look in the past of OCT is taken and the key basic physical principles of this imaging technology are explained and the future directions of this exceptional technique are commented on.
Abstract: Over the 15 years since the original description, optical coherence tomography (OCT) has become one of the key diagnostic technologies in the ophthalmic subspecialty areas of retinal diseases and glaucoma. The reason for the widespread adoption of this technology originates from at least two properties of the OCT results: on the one hand, the results are accessible to the non-specialist where microscopic retinal abnormalities are grossly and easily noticeable; on the other hand, results are reproducible and exceedingly quantitative in the hands of the specialist. However, as in any other imaging technique in ophthalmology, some artifacts are expected to occur. Understanding of the basic principles of image acquisition and data processing as well as recognition of OCT limitations are crucial issues to using this equipment with cleverness. Herein, we took a brief look in the past of OCT and have explained the key basic physical principles of this imaging technology. In addition, each of the several steps encompassing a third generation OCT evaluation of retinal tissues has been addressed in details. A comprehensive explanation about next generation OCT systems has also been provided and, to conclude, we have commented on the future directions of this exceptional technique.
TL;DR: Investigation of the automatic delineation of the outer limits of the macular neural retina by using the optical coherence tomography (OCT)-3 built-in software foundorrect delineators are occurring with the automated retinal thickness measurement tool of the OCT3 software.
Abstract: PURPOSE. To investigate the automatic delineation of the outer limits of the macular neural retina, by using the optical coherence tomography (OCT)-3 built-in software, and to determine its intluence in assessing retinal thickness in the normal macula. METHODS. Retrospective analysis of the OCT3 data at a tertiary-care referral center was performed to study the automatic delineation of the outer neural retina boundary generated by the OCT built-in software. In parallel, a cross-sectional study was designed to compare retinal thickness measurements obtained at specific macular regions of nine normal eyes by the automatic measurement tool with those obtained using a manual-caliper-assisted technique. RESULTS. OCT data from 121 eyes were evaluated. Two parallel, linear highly reflective layers (HRL) were visible at the level of the outer retinal boundary in normal macular regions. Disappearance of the inner and maintenance of the outer HRL was noted in the presence of eye conditions affecting the external retinal layers. The automated software delineation for the outer retinal border was primarily guided by the presence of the inner HRL, whereas the correlation of the OCT findings with the expected clinical and angiographic features on eyes presenting specific macular conditions pointed toward a deeper retinal pigment epithelium-retina interface occurring at the level of the outer HRL. There was a statistically significant difference between the retinal thickness in specific normal macular regions obtained by the automatic measurement tool and the caliper-assisted technique in which the outer retinal border delineation was based on the outer HRL (P = 0.008, Wilcoxon signed rank test). CONCLUSIONS. Incorrect delineation of the Outer neural retina boundary is occurring with the automated retinal thickness measurement tool of the OCT3 software. At specific regions of the normal macula, retinal thicknesses were significantly underestimated due to such misalignment.
TL;DR: The results show that the real part of n2 in ruby is an order of magnitude larger than the imaginary part, which clarifies the controversy about the dispersive or absorptive origin of the phase conjugation in ruby- and cromium-doped crystals.
Abstract: A differential interferometric method for direct measurements of the real part of the nonlinear index of refraction n2 has been developed. With this method we were able to measure n2 as low as 10−10 cm2/W. This method was used to measure n2 in both ruby and GdAlO3:Cr+3 for the first time. Our results show that the real part of n2 in ruby is an order of magnitude larger than the imaginary part. This result clarifies the controversy about the dispersive or absorptive origin of the phase conjugation in ruby- and cromium-doped crystals.
TL;DR: In this article, the authors show how the low-magnetic-field energy level structure of a single-electron atom gives rise to the quasi-Landau resonances as the field is increased.
Abstract: Highly resolved spectra are presented which show how the low-magnetic-field energylevel structure of a single-electron atom gives rise to the quasi-Landau resonances as the field is increased. Data from the strong-mixing region where electric and magnetic forces are comparable reveal that evenly spaced energy levels are a general feature, irrespective of parity and magnetic quantum number of the states. The quasi-Landau resonances emerge by a concentration of oscillator strength into a single level of each term.
TL;DR: In this article, optical coherence tomography is used for high-resolution, noninvasive imaging of the human retina, including the macula and optic nerve head in normal human subjects.
Abstract: Objective: To demonstrate optical coherence tomography for high-resolution, noninvasive imaging of the human retina. Optical coherence tomography is a new imaging technique analogous to ultrasound B scan that can provide cross-sectional images of the retina with micrometer-scale resolution. Design: Survey optical coherence tomographic examination of the retina, including the macula and optic nerve head in normal human subjects. Settings Research laboratory. Participants: Convenience sample of normal human subjects. Main Outcome Measures: Correlation of optical coherence retinal tomographs with known normal retinal anatomy. Results: Optical coherence tomographs can discriminate the cross-sectional morphologic features of the fovea and optic disc, the layered structure of the retina, and normal anatomic variations in retinal and retinal nerve fiber layer thicknesses with 10- μm depth resolution. Conclusion: Optical coherence tomography is a potentially useful technique for high depth resolution, cross-sectional examination of the fundus.
TL;DR: In this article, the diffraction tomography theorem is adapted to one-dimensional length measurement and the resulting spectral interferometry technique is described and the first length measurements using this technique on a model eye and on a human eye in vivo are presented.
Abstract: The diffraction tomography theorem is adapted to one-dimensional length measurement. The resulting spectral interferometry technique is described and the first length measurements using this technique on a model eye and on a human eye in vivo are presented.
TL;DR: A framework is proposed for understanding what is meant by the question, 'Does structural damage precede functional damage in glaucoma?' and the need to distinguish between "statistical" and "relational" meanings of this question.
Abstract: While it is often said that structural damage due to glaucoma precedes functional damage, it is not always clear what this statement means. This review has two purposes: first, to show that a simple linear relationship describes the data relating a particular functional test (standard automated perimetry (SAP)) to a particular structural test (optical coherence tomography (OCT)); and, second, to propose a general framework for relating structural and functional damage, and for evaluating if one precedes the other. The specific functional and structural tests employed are described in Section 2. To compare SAP sensitivity loss to loss of the retinal nerve fiber layer (RNFL) requires a map that relates local field regions to local regions of the optic disc as described in Section 3. When RNFL thickness in the superior and inferior arcuate sectors of the disc are plotted against SAP sensitivity loss (dB units) in the corresponding arcuate regions of the visual field, RNFL thickness becomes asymptotic for sensitivity losses greater than about 10dB. These data are well described by a simple linear model presented in Section 4. The model assumes that the RNFL thickness measured with OCT has two components. One component is the axons of the retinal ganglion cells and the other, the residual, is everything else (e.g. glial cells, blood vessels). The axon portion is assumed to decrease in a linear fashion with losses in SAP sensitivity (in linear units); the residual portion is assumed to remain constant. Based upon severe SAP losses in anterior ischemic optic neuropathy (AION), the residual RNFL thickness in the arcuate regions is, on average, about one-third of the premorbid (normal) thickness of that region. The model also predicts that, to a first approximation, SAP sensitivity in control subjects does not depend upon RNFL thickness. The data (Section 6) are, in general, consistent with this prediction showing a very weak correlation between RNFL thickness and SAP sensitivity. In Section 7, the model is used to estimate the proportion of patients showing statistical abnormalities (worse than the 5th percentile) on the OCT RNFL test before they show abnormalities on the 24-2 SAP field test. Ignoring measurement error, the patients with a relatively thick RNFL, when healthy, will be more likely to show significant SAP sensitivity loss before statistically significant OCT RNFL loss, while the reverse will be true for those who start with an average or a relatively thin RNFL when healthy. Thus, it is important to understand the implications of the wide variation in RNFL thickness among control subjects. Section 8 describes two of the factors contributing to this variation, variations in the position of blood vessels and variations in the mapping of field regions to disc sectors. Finally, in Sections 7 and 9, the findings are related to the general debate in the literature about the relationship between structural and functional glaucomatous damage and a framework is proposed for understanding what is meant by the question, 'Does structural damage precede functional damage in glaucoma?' An emphasis is placed upon the need to distinguish between "statistical" and "relational" meanings of this question.
TL;DR: A brief history of OCT development is presented, current clinical applications are reviewed, some clinical translation challenges are discussed, and laboratory developments poised for future clinical application are reviewed.
Abstract: Since its introduction, optical coherence tomography OCT technology has advanced from the laboratory bench to the clinic and back again. Arising from the fields of low coherence inter- ferometry and optical time- and frequency-domain reflectometry, OCT was initially demonstrated for retinal imaging and followed a unique path to commercialization for clinical use. Concurrently, sig- nificant technological advances were brought about from within the research community, including improved laser sources, beam delivery instruments, and detection schemes. While many of these technolo- gies improved retinal imaging, they also allowed for the application of OCT to many new clinical areas. As a result, OCT has been clinically demonstrated in a diverse set of medical and surgical specialties, in- cluding gastroenterology, dermatology, cardiology, and oncology, among others. The lessons learned in the clinic are currently spurring a new set of advances in the laboratory that will again expand the clinical use of OCT by adding molecular sensitivity, improving image quality, and increasing acquisition speeds. This continuous cycle of laboratory development and clinical application has allowed the OCT technology to grow at a rapid rate and represents a unique model for the translation of biomedical optics to the patient bedside. This work presents a brief history of OCT development, reviews current clinical applications, discusses some clinical translation challenges, and re- views laboratory developments poised for future clinical application.
TL;DR: There is modest correlation between OCT-measured center point thickness and visual acuity, and modest correlation of changes in retinal thickening andVisual acuity after focal laser treatment for DME, however, a wide range of visual Acuity may be observed for a given degree of retinal edema.
Abstract: Objective To compare optical coherence tomography (OCT)-measured retinal thickness and visual acuity in eyes with diabetic macular edema (DME) both before and after macular laser photocoagulation Design Cross-sectional and longitudinal study Participants Two hundred ten patients (251 eyes) with DME enrolled in a randomized clinical trial of laser techniques Methods Retinal thickness was measured with OCT and visual acuity was measured with the electronic Early Treatment of Diabetic Retinopathy procedure Main outcome measures Optical coherence tomography-measured center point thickness and visual acuity Results The correlation coefficients for visual acuity versus OCT center point thickness were 052 at baseline and 049, 036, and 038 at 35, 8, and 12 months after laser photocoagulation The slope of the best fit line to the baseline data was approximately 44 letters (95% confidence interval, 35-53) of better of visual acuity for every 100-mum decrease in center point thickness at baseline with no important difference at follow-up visits Approximately one third of the variation in visual acuity could be predicted by a linear regression model that incorporated OCT center point thickness, age, hemoglobin A1C, and severity of fluorescein leakage The correlation between change in visual acuity and change in OCT center point thickening 35 months after laser treatment was 044, with no important difference at the other follow-up times A subset of eyes showed paradoxical improvements in visual acuity with increased center point thickening (7%-17% at the 3 time points) or paradoxical worsening of visual acuity with a decrease in center point thickening (18%-26% at the 3 time points) Conclusions There is modest correlation between OCT-measured center point thickness and visual acuity, and modest correlation of changes in retinal thickening and visual acuity after focal laser treatment for DME However, a wide range of visual acuity may be observed for a given degree of retinal edema Thus, although OCT measurements of retinal thickness represent an important tool in clinical evaluation, they cannot substitute reliably as a surrogate for visual acuity at a given point in time This study does not address whether short-term changes on OCT are predictive of long-term effects on visual acuity