Fourier-domain Optical Coherence Tomography Research Articles

Electrophysiological and Anatomical Correlates of Spinal Cord Optical Coherence Tomography.

Despite the continuous improvement in medical imaging technology, visualizing the spinal cord poses severe problems due to structural or incidental causes, such as small access space and motion artifacts. In addition, positional guidance on the spinal cord is not commonly available during surgery, with the exception of neuronavigation techniques based on static pre-surgical data and of radiation-based methods, such as fluoroscopy. A fast, bedside, intraoperative real-time imaging, particularly necessary during the positioning of endoscopic probes or tools, is an unsolved issue. The objective of our work, performed on experimental rats, is to demonstrate potential intraoperative spinal cord imaging and probe guidance by optical coherence tomography (OCT). Concurrently, we aimed to demonstrate that the electromagnetic OCT irradiation exerted no particular effect at the neuronal and synaptic levels. OCT is a user-friendly, low-cost and endoscopy-compatible photonics-based imaging technique. In particular, by using a Fourier-domain OCT imager, operating at 850 nm wavelength and scanning transversally with respect to the spinal cord, we have been able to: 1) accurately image tissue structures in an animal model (muscle, spine bone, cerebro-spinal fluid, dura mater and spinal cord), and 2) identify the position of a recording microelectrode approaching and inserting into the cord tissue 3) check that the infrared radiation has no actual effect on the electrophysiological activity of spinal neurons. The technique, potentially extendable to full three-dimensional image reconstruction, shows prospective further application not only in endoscopic intraoperative analyses and for probe insertion guidance, but also in emergency and adverse situations (e.g. after trauma) for damage recognition, diagnosis and fast image-guided intervention.

Optical coherence tomography images simulated with an analytical solution of Maxwell's equations for cylinder scattering.

An algorithm for the simulation of image formation in Fourier domain optical coherence tomography (OCT) for an infinitely long cylinder is presented. The analytical solution of Maxwell’s equations for light scattering by a single cylinder is employed for the case of perpendicular incidence to calculate OCT images. The A-scans and the time-resolved scattered intensities are compared to geometrical optics results calculated with a ray tracing approach. The reflection peaks, including the whispering gallery modes, are identified. Additionally, the Debye series expansion is employed to identify single peaks in the OCT A-scans. Furthermore, a Gaussian beam is implemented in order to simulate lateral scanning over the cylinder for two-dimensional B-scans. The fields are integrated over a certain angular range to simulate a detection aperture. In addition, the solution for light scattering by layered cylinders is employed and the various layers are identified in the resulting OCT image. Overall, the simulations in this work show that OCT images do not always display the real surface of investigated samples.

Consistency of corneal sublayer thickness measurements using Fourier-domain optical coherence tomography after phacoemulsification.

To assess the reliability of corneal epithelial thickness (CET), nonepithelial central corneal thickness (NECCT), and central corneal thickness (CCT) measurements using Cirrus high-definition optical coherence tomography (HD-OCT) in patients who did and did not undergo cataract surgery. Forty patients who underwent uneventful phacoemulsification and 40 healthy participants were recruited to evaluate the intraobserver repeatability and interobserver reproducibility of CET, NECCT, and CCT measurements using Cirrus HD-OCT. To analyze repeatability, one examiner obtained 5 consecutive scans in each participant; for interobserver reproducibility, another examiner randomly obtained another scan. Within-subject standard deviation, coefficient of variation (CV), limits of agreement, and intraclass correlation coefficient (ICC) data were obtained. For intraobserver repeatability, the intrasession CV (CVw) and ICC values of the CET in the operated and nonoperated groups were 3.7% and 0.80 and 3.8% and 0.73, respectively; for NECCT, 0.7% and 0.98 and 0.8% and 0.97; and for CCT, 0.6% and 0.99 and 0.7% and 0.98. For interobserver reproducibility, the CVw and ICC values for the CET in the operated and nonoperated groups were 2.6% and 0.82 and 2.3% and 0.62, respectively; for NECCT, 0.7% and 0.98 and 0.5% and 0.98; and for CCT, 0.5% and 0.99 and 0.4% and 0.99. The corneal sublayer thickness can be measured reliably using Cirrus HD-OCT in patients who underwent cataract surgery and elderly participants; however, the CET consistency is poorer than the NECCT. Corneal epithelial thickness modifications exceeding 4% reflect true thickness changes instead of random error variations using HD-OCT.

Longitudinal and Cross-Sectional Analyses of Age Effects on Retinal Nerve Fiber Layer and Ganglion Cell Complex Thickness by Fourier-Domain OCT.

PurposeWe studied the effects of age and intraocular pressure (IOP) on retinal nerve fiber layer (NFL) and macular ganglion cell complex (GCC) thickness in normal eyes.MethodsData from subjects from the multicenter Advanced Imaging for Glaucoma Study (AIGS) were analyzed. The data included yearly visits from the normal subjects in the AIGS study. Fourier-domain optical coherence tomography (FD-OCT) was used to measure retinal NFL and macular GCC on each visit. Mixed effect models were used to evaluate the longitudinal effect of age and IOP on the NFL and GCC thickness. The measurements at baseline were used to examine the cross-sectional effects.ResultsThe analysis included 192 eyes (92 participants) from AIGS between 2009 and 2013. The longitudinal analyses showed overall GCC thickness decreased 0.25 ± 0.05 μm per year (P < 0.001) while the overall NFL thickness decreased 0.14 ± 0.07 μm per year (P = 0.04). The cross-sectional analyses showed the GCC thickness was 0.17 ± 0.05 μm thinner per year of baseline age (P < 0.001), while the NFL was 0.21 ± 0.06 μm thinner (P < 0.001). There was no significant IOP effect on either GCC or NFL from either the longitudinal or cross-sectional analysis.ConclusionsLongitudinal and cross-sectional analyses provided consistent rates of approximately 0.2% per year of age-related thinning in NFL and GCC thicknesses. This is relevant in establishing criteria to detect glaucoma-related thinning (disease progression) in excess of normal aging. IOP does not seem to be a significant confounder for progression analysis.Translational RelevanceThis study demonstrated the relevance of advanced imaging technology in diagnosing and monitoring glaucoma disease.

Corneal Epithelium Thickness Profile in 614 Normal Chinese Children Aged 7-15 Years Old.

The purpose of the study is to describe the values and distribution of corneal epithelium thickness (CET) in normal Chinese school-aged children, and to explore associated factors with CET. CET maps were measured by Fourier-domain optical coherence tomography (FD-OCT) in normal Chinese children aged 7 to 15 years old from two randomly selected schools in Shanghai, China. Children with normal intraocular pressure were further examined for cycloplegic autorefraction, corneal curvature radius (CCR) and axial length. Central (2-mm diameter area), para-central (2- to 5-mm diameter area), and peripheral (5- to 6-mm diameter area) CET in the superior, superotemporal, temporal, inferotemporal, inferior, inferonasal, nasal, superonasal cornea; minimum, maximum, range, and standard deviation of CET within the 5-mm diameter area were recorded. The CET was thinner in the superior than in the inferior and was thinner in the temporal than in the nasal. The maximum CET was located in the inferior zone, and the minimum CET was in the superior zone. A thicker central CET was associated with male gender (p = 0.009) and older age (p = 0.037) but not with CCR (p = 0.061), axial length (p = 0.253), or refraction (p = 0.351) in the multiple regression analyses. CCR, age, and gender were correlated with para-central and peripheral CET.

Can diagnostic accuracy for early glaucoma be improved in Japanese? A trial with a potential new parameter of the RTVue OCT

Aim: To evaluate the diagnostic accuracy of the ratio of circumpapillary retinal nerve fiber layer thickness (cpRNFLT) to macular outer retinal thickness (R/O ratio) and the ratio of ganglion cell complex (GCC) thickness to outer retinal thickness (G/O ratio) measured with the RTVue-100 Fourier-domain optical coherence tomograph for detecting early glaucoma in Japanese eyes.Methods: Forty-seven healthy control, 31 preperimetric and 70 early perimetric glaucoma eyes. We used cpRNFLT and macular retinal thickness measurements to calculate new ratio parameters, and to compare their diagnostic accuracy to those of the manufacturer-provided parameters of the RTVue-100. The ability of each parameter to diagnose glaucoma was examined by comparing the area under the receiver-operating characteristics curve (AUROC).Results: AUROC values for the healthy vs. preperimetric glaucoma comparison were 0.842, 0.859, and 0.925 for average cpRNFLT, average R/O ratio, and average G/O ratio, respectively. For the healthy vs. early perimetric glaucoma comparison the AUROC values were 0.927, 0.933, and 0.979 for cpRNFLT, R/O ratio, and G/O ratio, respectively. Diagnostic accuracy of the R/O ratio and cpRNFLT did not differ significantly (P &gt; 0.05). Diagnostic accuracy for the G/O ratio was significantly greater than the cpRNFLT in early glaucoma (P &lt; 0.05).Conclusions: Use of the G/O ratio is recommended for the detection of early glaucoma in Japanese eyes.

Minimally invasive surgical method to detect sound processing in the cochlear apex by optical coherence tomography.

Sound processing in the inner ear involves separation of the constituent frequencies along the length of the cochlea. Frequencies relevant to human speech (100 to 500 Hz) are processed in the apex region. Among mammals, the guinea pig cochlear apex processes similar frequencies and is thus relevant for the study of speech processing in the cochlea. However, the requirement for extensive surgery has challenged the optical accessibility of this area to investigate cochlear processing of signals without significant intrusion. A simple method is developed to provide optical access to the guinea pig cochlear apex in two directions with minimal surgery. Furthermore, all prior vibration measurements in the guinea pig apex involved opening an observation hole in the otic capsule, which has been questioned on the basis of the resulting changes to cochlear hydrodynamics. Here, this limitation is overcome by measuring the vibrations through the unopened otic capsule using phase-sensitive Fourier domain optical coherence tomography. The optically and surgically advanced method described here lays the foundation to perform minimally invasive investigation of speech-related signal processing in the cochlea.

Identification of iridocorneal angle structures assessed by Fourier domain optical coherence tomography

ObjectiveTo study the structures of the iridocorneal angle using anterior segment optical coherence tomography (OCT) defining their tomographic characteristics and quantifying their identification frequency. Material and methodsA cross-sectional study was performed on 267 right eyes of 267 consecutive healthy patients. Fourier domain OCT RTVue (Optovue Inc, CA, EE. UU.) was used to examine the iridocorneal angle in the nasal and temporal sectors. The structures evaluated were: sclerocorneal limbus, sclerocorneal transition, Schwalbe's line, trabecular meshwork, Schlemm's canal, scleral spur, and angular recess. Within and between agreements to identify structures were calculated using Cohen's kappa coefficient. ResultsThe mean age was 41.3±14.3 years (range 20–80), with 57% being women. The sclerocorneal limbus, sclerocorneal transition, and Schwalbe's line were identified by 98.7, 97 and 93.4% of the images, respectively, with the trabecular meshwork and Schlemm's canal being identified in 91% of cases. The scleral spur could be identified in 85.4%, and the angular recess in 74.5%. There was no difference in the identification between the temporal and nasal sectors. Within and between agreement was k=0.92 and k=0.88, respectively, in the identification of the structures of the total images studied. ConclusionsFourier domain OCT is a reliable technique for the identification of the structures of the iridocorneal angle, among which can be highlighted are, the trabecular meshwork, Schlemm's canal, scleral spur, and Schwalbe's line.

Subclinical keratoconus detection by pattern analysis of corneal and epithelial thickness maps with optical coherence tomography

To screen for subclinical keratoconus by analyzing corneal, epithelial, and stromal thickness map patterns with Fourier-domain optical coherence tomography (OCT). Four centers in the United States. Cross-sectional observational study. Eyes of normal subjects, subclinical keratoconus eyes, and the topographically normal eye of a unilateral keratoconus patient were studied. Corneas were scanned using a 26,000 Hz Fourier-domain OCT system (RTVue). Normal subjects were divided into training and evaluation groups. Corneal, epithelial, and stromal thickness maps and derived diagnostic indices, including pattern standard deviation (PSD) variables and pachymetric map-based keratoconus risk scores, were calculated from the OCT data. Area under the receiver operating characteristic curve (AUC) analysis was used to evaluate the diagnostic accuracy of the indices. The study comprised 150 eyes of 83 normal subjects, 50 subclinical keratoconus eyes of 32 patients, and 1 topographically normal eye of a unilateral keratoconus patient. Subclinical keratoconus was characterized by inferotemporal thinning of the cornea, epithelium, and stroma. The PSD values for corneal (P < .001), epithelial (P < .001), and stromal (P = .049) thickness maps were all significantly higher in subclinical keratoconic eyes than in the normal group. The diagnostic accuracy was significantly higher for PSD variables (pachymetric PSD, AUC = 0.941; epithelial PSD, AUC = 0.985; stromal PSD, AUC = 0.924) than for the pachymetric map-based keratoconus risk score (AUC = 0.735). High-resolution Fourier-domain OCT could map corneal, epithelial, and stromal thicknesses. Corneal and sublayer thickness changes in subclinical keratoconus could be detected with high accuracy using PSD variables. These new diagnostic variables might be useful in the detection of early keratoconus. Oregon Health and Science University (OHSU) and Drs. Li, Tan, and Huang have a significant financial interest in Optovue, Inc. These potential conflicts have been reviewed and managed by OHSU. Dr. Brass receives research grants from Optovue, Inc. Drs. Chamberlain and Weiss have no financial or proprietary interest in any material or method mentioned.

Spectral fusing Gabor domain optical coherence microscopy.

Gabor domain optical coherence microscopy (GD-OCM) is one of many variations of optical coherence tomography (OCT) techniques that aims for invariant high resolution across a 3D field of view by utilizing the ability to dynamically refocus the imaging optics in the sample arm. GD-OCM acquires multiple cross-sectional images at different focus positions of the objective lens, and then fuses them to obtain an invariant high-resolution 3D image of the sample, which comes with the intrinsic drawback of a longer processing time as compared to conventional Fourier domain OCT. Here, we report on an alternative Gabor fusing algorithm, the spectral-fusion technique, which directly processes each acquired spectrum and combines them prior to the Fourier transformation to obtain a depth profile. The implementation of the spectral-fusion algorithm is presented and its performance is compared to that of the prior GD-OCM spatial-fusion approach. The spectral-fusion approach shows twice the speed of the spatial-fusion approach for a spectrum size of less than 2000 point sampling, which is a commonly used spectrum size in OCT imaging, including GD-OCM.

Is optical coherence tomography an effective device for evaluation of tear film meniscus in patients with acne rosacea?

To investigate the tear meniscus using Fourier-domain optical coherence tomography (FD-OCT) in patients with acne rosacea and to determine the relationship between tear film break-up tests (TBUT), Schirmer test and FD-OCT values and to compare them with that of healthy controls. One hundred and four patients with acne rosacea and 104 body mass index age-sex-matched healthy subjects were enrolled in this prospective case-control study. Tear meniscus height (TMH), tear meniscus depth (TMD), and tear meniscus cross-sectional area (TMA) were measured using FD-OCT (RTVue-100); TBUT, Schirmer test and dry eye questionnaire (OSDI) were evaluated. Correlation was assessed using Spearman's correlation coefficient. Mean TMH, TMD, TMA, TBUT, and Schirmer test values of acne rosacea patients were significantly lower than and OSDI score significantly higher than those of controls. Tear mensicus values were significantly correlated with OSDI scores, TBUT, and Schirmer test results. The intraobserver intraclass correlation coefficient (ICC) for tear parameters ranged from 0.90 to 0.96 and interobserver ICC ranged from 0.92 to 0.94, which revealed high reproducibility for all measurements parameters both acne rosacea and control subjects. Accuracy of dry eye diagnosis by FD-OCT was 60.4% for TMH, 58.7% for TMD, and 64.8% for TMA. Tear meniscus measurement with FD-OCT could provide acceptable specificity and sensitivity in diagnosis of dry eye in acne rosacea patients.

Corneal Thickness Profile and Associations in Chinese Children Aged 7 to 15 Years Old.

Corneal thickness (CT) maps of the central (2-mm diameter), para-central (2 to 5-mm diameter), peripheral (5 to 6-mm diameter), and minimum (5-mm diameter) cornea were measured in normal Chinese school children aged 7 to 15 years old using Fourier-domain optical coherence tomography. Multiple regression analyses were performed to explore the effect of associated factors [age, gender, refraction, axial length and corneal curvature radius (CCR)] on CT and the relationship between central corneal thickness (CCT) and intraocular pressure (IOP). A total of 1228 eyes from 614 children were analyzed. The average CCT was 532.96 ± 28.33 μm for right eyes and 532.70 ±28.45 μm for left eyes. With a 10 μm increase in CCT, the IOP was elevated by 0.37 mm Hg, as measured by noncontact tonometry. The CT increased gradually from the center to the periphery. The superior and superior nasal regions had the thickest CTs, while the thinnest points were primarily located in the inferior temporal cornea. The CCT was associated with CCR (p = 0.008) but not with gender (p = 0.075), age (p = 0.286), axial length (p = 0.405), or refraction (p = 0.985). In the para-central region and the peripheral cornea, increased CT was associated with younger age, male gender, and a flatter cornea.

Comparative study of the fourier-domain optical coherence tomography structural changes and visual field loss for early detection of glaucoma

Objective To evaluate the macular ganglion cell complex (GCC) and retinal nerve fiber layer (RNFL) measurements with Fourier-domain optical coherence tomography (FDOCT) for the detection of early glaucoma and to compare the results with visual field (VF) defects. Design This was a cross-sectional prospective diagnostic study. Patients and methods This study included 10 normal eyes and 48 eyes of patients suspected of having glaucoma on the basis of the appearance of the optic disc. All eyes had normal VFs by standard automated perimetry before the imaging session. A FDOCT system was used to map the macula and peripapillary regions of the retina. Short-wave automated perimetry was performed. Areas under the receiver operating characteristic curves (AUC) were calculated to summarize the diagnostic accuracies of the parameters. Results The AUCs for the VF parameters were 0.819 for the mean deviation and 0.911 for the pattern standard deviation. AUCs for the RNFL parameters ranged from 0.625 for the superior average thickness to 0.693 for the inferior average RNFL thickness. AUCs for the macular parameters ranged from 0.467 for the GCC–global loss volume to 0.556 for the inferior GCC thickness. The AUC of the VF parameter with the largest AUC, pattern standard deviation, was significantly higher than that of the RNFL and macular parameters (0.911 vs. 0.693 and 0.556). Conclusion GCC measurements with FDOCT were similar to the RNFL parameters, but were inferior to VF deficits on short-wave automated perimetry for early detection of glaucoma.

Correlation of Retinal Nerve Fiber Layer Thickness and Axial Length on Fourier Domain Optical Coherence Tomography.

The assessment of the peripapillary Retinal Nerve Fiber Layer (RNFL) thickness has been an important tool for evaluating and diagnosing glaucoma and its progression. Literature suggests that myopic eyes are at an increased risk for developing glaucoma. This study gives an insight into the relationship of RNFL thickness to the axial length in normal population. To correlate the RNFL thickness and the axial length in normal individuals with Fourier domain Optical Coherence Tomography (OCT). In the current study, 298 eyes of 149 normal individuals (10 years or older) with or without refractive error were recruited. The RNFL thickness was measured using Optovue (RTVue) three-dimensional Fourier domain OCT. We observed an inverse relationship between average RNFL thickness and increasing axial length(p=0.003). Maximum RNFL thickness was seen in the Infero-Temporal (IT) quadrant and minimum in the Supero-Nasal (SN) quadrant. RNFL thickness did not show any tendency to decline with age using the Pearsons correlation (r=0.07). Females had an increased RNFL thickness in the Supero-Temporal (ST) and Infero-Nasal (IN) quadrant (p-value 0.046 and 0.02) in comparison to males. There was a statistically significant thinning in Ganglion Cell Complex (GCC) with increasing axial length (p-value 0.000). The current study suggests that the average RNFL thickness does not decrease with age. The RNFL and GCC thickness shows an inverse correlation with axial length of the eyeball hence observations have to be carefully interpreted in myopic eyes. Clinicians need to keep the anatomical variations in RNFL for better patient management.

Assessment of Corneal Epithelial Thickness in Asymmetric Keratoconic Eyes and Normal Eyes Using Fourier Domain Optical Coherence Tomography.

Purpose. To compare the characteristics of asymmetric keratoconic eyes and normal eyes by Fourier domain optical coherence tomography (OCT) corneal mapping. Methods. Retrospective corneal and epithelial thickness OCT data for 74 patients were compared in three groups of eyes: keratoconic (n = 22) and normal fellow eyes (n = 22) in patients with asymmetric keratoconus and normal eyes (n = 104) in healthy subjects. Areas under the curve (AUC) of receiver operator characteristic (ROC) curves for each variable were compared across groups to indicate their discrimination capacity. Results. Three variables were found to differ significantly between fellow eyes and normal eyes (all p < 0.05): minimum corneal thickness, thinnest corneal point, and central corneal thickness. These variables combined showed a high discrimination power to differentiate fellow eyes from normal eyes indicated by an AUC of 0.840 (95% CI: 0.762–0.918). Conclusions. Our findings indicate that topographically normal fellow eyes in patients with very asymmetric keratoconus differ from the eyes of healthy individuals in terms of their corneal epithelial and pachymetry maps. This type of information could be useful for an early diagnosis of keratoconus in topographically normal eyes.

Myelinated Retinal Nerve Fibers in Children: OCT Imaging, Refractive Error and Vision

Purpose: To characterize peripapillary retinal nerve fiber layers (RNFL’s) and macular retinal structure in children with unilateral myelinated retinal nerve fibers (MRNFs). We also investigated the correlation between MRNF abnormalities and refractive error/visual acuity. Methods: Twelve children (7-13 years old) with MRNFs were included. Fourier domain optical coherence tomography was used to image both the peripapillary RNFL and the macular retinal structures in 6 patients. Using the instrument’s segmentation software, global RNFL thickness and central subfield thickness (CST) of the macula were analyzed. Planimetry was used to quantify the MRNF area observed on fundus photography. Visual acuity and cycloplegic refractive errors (spherical equivalent) were also recorded. Results from the MRNF-affected eye were compared with the fellow eye. Results: The global RNFL thickness of the eyes with MRNFs (152 ± 13.9 μm) was significantly higher than the fellow eyes (114.3 ± 15.2 μm) (P=0.003). The global RNFL thickness of the fellow eye was in normal range, and no significant differences were detected in macular CST between the eyes with MRNFs and fellow eyes (P=0.403). The MRNF area was significantly correlated with the spherical equivalent of the affected eye (P=0.002). In addition, the interocular difference of RNFL thickness between eyes was significantly correlated with anisometropia (P=0.03). Conclusions: Eyes with MRNFs show a significantly thicker global peripapillary RNFL trend as compared to the fellow eye, and the area of MRNFs is correlated with the development of myopia and anisometropia, but not correlated to visual acuity.

Observation Study of the Retina with the Alzheimer’s Disease or Amnestic Mild Cognitive Impairment Patients

Objective: We investigated the regularity changes of the retinal nerve fiber layer (RNFL) and macular ganglion cell complex (mGCC) of the Alzheimer’s disease (AD) and amnestic Mild Cognitive Impairment (aMCI) patients. Methods: 24 AD patients, 22 aMCI patients and 30 health controls whose age were above 60 years old were recruited in the study. The RNFL thickness and the mGCC average thickness were measured by Fourier-domain optical coherence tomography (FD-OCT). Results: Compared with the controls, we found statistically significant lower of the intraocular pressure (IOP) in the AD and aMCI patients. When compared with the AD patients and controls, aMCI patients showed a significant decrease in RNFL thickness in ST (Superior Temporal), TU (Temporal Upper) and temporal (TU+TL) quadrants. The average thickness of the mGCC was significantly thinner in the aMCI patients than in the AD patients and Controls. The Gross Loss of Volume (GLV) was significantly higher in the aMCI group than in the patients and Controls. Conclusion: AD and aMCI patients had lower IOP, but there was no evidence that IOP would decrease with the progression of disease. Retinal degeneration in the aMCI patients detected by OCT may be a pathological indicator of the disease.

Влияние версии программного обеспечения ОКТ на обнаружение изменений в комплексе ганглионарных клеток сетчатки при экстракции катаракты

Влияние версии программного обеспечения ОКТ на обнаружение изменений в комплексе ганглионарных клеток сетчатки при экстракции катаракты

In vivo wide-field multispectral scanning laser ophthalmoscopy-optical coherence tomography mouse retinal imager: longitudinal imaging of ganglion cells, microglia, and Müller glia, and mapping of the mouse retinal and choroidal vasculature.

Scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT) provide complementary views of the retina, with the former collecting fluorescence data with good lateral but relatively low-axial resolution, and the latter collecting label-free backscattering data with comparable lateral but much higher axial resolution. To take maximal advantage of the information of both modalities in mouse retinal imaging, we have constructed a compact, four-channel, wide-field (∼50 deg) system that simultaneously acquires and automatically coregisters three channels of confocal SLO and Fourier domain OCT data. The scanner control system allows “zoomed” imaging of a region of interest identified in a wide-field image, providing efficient digital sampling and localization of cellular resolution features in longitudinal imaging of individual mice. The SLO is equipped with a “flip-in” spectrometer that enables spectral “fingerprinting” of fluorochromes. Segmentation of retina layers and en face display facilitate spatial comparison of OCT data with SLO fluorescence patterns. We demonstrate that the system can be used to image an individual retinal ganglion cell over many months, to simultaneously image microglia and Müller glia expressing different fluorochromes, to characterize the distinctive spatial distributions and clearance times of circulating fluorochromes with different molecular sizes, and to produce unequivocal images of the heretofore uncharacterized mouse choroidal vasculature.

Identificación de estructuras del ángulo iridocorneal mediante tomografía de coherencia óptica de dominio Fourier

ObjectiveTo study the structures of the iridocorneal angle using anterior segment optical coherence tomography (OCT) defining their tomographic characteristics and quantifying their identification frequency. Material and methodsA cross-sectional study was performed on 267 right eyes of 267 consecutive healthy patients. Fourier domain OCT RTVue (Optovue Inc, CA, EE. UU.) was used to examine the iridocorneal angle in the nasal and temporal sectors. The structures evaluated were: Sclerocorneal limbus, sclerocorneal transition, Schwalbe's line, trabecular meshwork, Schlemm's canal, scleral spur, and angular recess. Within and between agreements to identify structures were calculated using Cohen's kappa coefficient. ResultsThe mean age was 41.3 ± 14.3 years (range 20-80), with 57% being women. The sclerocorneal limbus, sclerocorneal transition, and Schwalbe's line were identified by 98.7, 97 and 93.4% of the images, respectively, with the trabecular meshwork and Schlemm's canal being identified in 91% of cases. The scleral spur could be identified in 85.4%, and the angular recess in 74.5%. There was no difference in the identification between the temporal and nasal sectors. Within and between agreement was k=0.92 and k=0.88, respectively, in the identification of the structures of the total images studied. ConclusionsFourier domain OCT is a reliable technique for the identification of the structures of the iridocorneal angle, among which can be highlighted are, the trabecular meshwork, Schlemm's canal, scleral spur, and Schwalbe's line.