When the above data was analyzed including both the dry and nAMD patients there was a statistically significant decrease in the subfoveal choroidalthickness over 6 months
compared to baseline (p=0.049). On subgroup analysis however, it was clear that the nAMD patients, who made up the 61% of the cohort, drove this finding. The dry AMD patients did not demonstrate a statistically significant decrease over 6 months when examined as a subgroup. Although in both dry and nAMD groups there were some eyes that demonstrated an increase in choroidalthickness over 6 months, there was overall a statistically significant trend towards decreased choroidalthickness in the group considered as a whole. The increase in subfoveal thickness, which was observed in both subgroups, may represent an error intrinsic to manual measurements, or a natural variation in choroidalthickness. The choroid is a highly vascular structure whose thickness varies with intraocular pressure, perfusion pressure, nitric oxide production, and vasoactive substances such as circulating catecholamines, and is believed to be highly sensitive to small vessel disease, therefore it may be expected that there is some natural fluctuations of subfoveal choroidalthickness over time. 20-23. There is also known diurnal variation in choroidalthickness with the choroid being thickness at night and thinnest during the day. A recent study by Chakraborty et al demonstrated an average choroidalthickness of 0.256 +/− 0.049 mm with a diurnal fluctuation of 0.029 +/− 0.016 mm. Patients included in this study had OCT imaging performed at various times throughout the day and therefore there may be some choroidalthickness variation due to differences when the measurements were taken. 24 In normal eyes on the Cirrus OCT, Manjunath et al. reported a subfoveal choroidalthickness of 272 ± 81μm with a sample size of 34 subjects, and a mean age of 51.1 years (range, 22 to 78 years), as well as demonstrating the reproducibility of choroidalthickness measurements by the same technique described in this study, with strong inter-observer correlation r = 0.92, P < . 0001. 17 Previous studies have demonstrated a 1.56 um decline in choroidalthickness per
Quantitative Measurements of Choroidal Thick- ness. The choroidal map obtained from the 12-mm radial scans provided an automatic measurement of the subfoveal CT (central 1 mm) and the mean CT in nine subfields based on the Early Treatment Diabetic Retinopathy Study (ETDRS) grid ( Fig. 1 A). The inner ring (3-mm diameter) included the superior inner macula, temporal inner macula, inferior inner macula, and nasal inner macula. The outer ring (6- mm diameter) was comprised of the superior outer macula, temporal outer macula, inferior outer macula, and nasal outer macula (NOM). In addition, an aggregate field was defined as the total macula, corresponding to the mean CT of the nine subfields. The mean and SD and the coeffi- cient of variation (CV) of CT in each macular subfield (= SD/mean) were calculated. The TCP was determined on the 9 × 9-mm OCT-A CT map. The location of the TCP was determined by graphical representation of CT maps using the built-in manufacturer’s IMAGEnet 6 software and manually verified for all patients with the caliper by the observer (ST) on the corresponding B-scans. The position of the TCP was recorded on the choroidalthickness map, segmented into four quadrants ( Fig. 1 B). Furthermore, in order to allow a comparison with the previously published data, 9 , 12 subfoveal CT measurements were also performed
neovascularization such as intraretinal or subretinal fluid at any visit time point. This group included patients with geographic atrophy, drusen, and pigment epithelial detachments. Patients were subclassified as having wet AMD if there was evidence of neovascularization such as intraretinal or subretinal fluid at any visit time point. Patients were treated by different attending physicians with a combination of treat-and-extend and as-needed regimens with standard anti-VEGF therapy. Of the 40 eyes with wet AMD, 7 of these patients had undergone prior photodynamic therapy at least once in the study eye. The average duration of disease was 3.8 years. Subfoveal choroidalthickness measurements were used for comparative purposes in this study. The pattern of choroidalthickness in the macula in the 57 eyes with AMD in this study demonstrated the thickest choroid located subfoveally, with nasal and temporal thinning, maintaining a similar pattern seen in normal eyes (Figure 2). 11,16
The scan pattern used on Cirrus HD-OCT was HD 1-line raster. It is a 6-mm line consisting of 4,096 A-scans. Images were taken with the vitreoretinal interface adjacent to the zero- delay and were not inverted to bring the choroid adjacent to zero-delay as image inversion using the Cirrus software results in a low-quality image. The HD 1-line raster has 20 B- scans averaged together without tracking. To be included in this study, images had to be at least 6 of 10 in intensity and taken as close to the fovea as possible, by choosing to image the thinnest point of the macula, with the understanding that slight differences in positioning could affect the measured thicknesses. Using the Cirrus linear measurement tool, 2
Since 2006, a variety of spectral domain OCT instruments have become commercially available, therefore determining if choroidalthickness measurements were possible using another one of the commonly used spectral domain OCT devices is of interest. This report confirms that another simple, reproducible method for choroidal measurement using the Zeiss Cirrus HD-OCT device is possible in the majority of eyes. Reliable measurements of choroidalthickness were obtainable in nearly three quarters of examined eyes (74%). The results of this study were very similar to those reported previously using the Heidelberg OCT device. The mean subfoveal choroidalthickness was found to be 272 μm (SD, +/- 81 μm), compared to 287 μm (SD, +/- 76 μm) found in the study of normal eyes by Spaide et al. 3 As reported previously 3 , similar variability of choroidalthickness across the macula in normal eyes was observed, with the choroid thinnest proximal to the disc. Additionally, a negative correlation between both area and age and thickness and age was noted, suggesting that progressive choroidal thinning occurs over time in normal eyes, which is a similar finding to previous reports. In addition, this study suggests that area measurements might be another value useful to track changes in choroidalthickness.
Peripapillary choroidalthickness measurements
One way analysis of variance was used to determine whether average choroidalthickness differed among each of the 4 peripapillary regions. The analysis showed significant differences among the groups (p< 0.001; Table 1). Geographic differences existed among the four quadrants. The superior, nasal and temporal quadrants had thicker average choroidalthickness at 229.41 ± 50.96 μm (mean ± standard deviation), 227.17 ± 81.40 μm and 208.84 ± 55.70 μm, respectively. The inferior quadrant had the thinnest peripapillary choroidalthickness among all four quadrants (149.90 ±5 0.14 μm). Post-hoc analysis utilizing the Scheffé method demonstrated that the inferior peripapillary choroid was significantly thinner compared to all other quadrants (p≤ 0.001; Table 2). However, none of the other quadrants (superior, nasal or temporal) demonstrated significant differences with each other. The thickness of the peripapillary choroid generally increased moving distally from the optic nerve, and then approaching a plateau (Figure 2). The exception was in the nasal quadrant, where the choroidalthickness actually decreased at 1500 μm away from the optic nerve and then reached a plateau. The average thickness of the inferior quadrant was significantly thinner than all others at all distances measured away from the optic nerve (p< 0.001). Inter-grader reproducibility
Optical coherence tomography (OCT) can provide depth- resolved information on the posterior eye and is gaining acceptance as a tool for in vivo choroidal imaging. However, the majority of studies on the choroid using OCT have focused on choroidalthickness measurements or imaging larger choroidal vessels, and to date, only a few studies have demonstrated choriocapillaris imaging consistent with histological and electron micrograph corrosion casts findings, in terms of capillary density. Using OCT phase information, Kurokawa et al. demonstrated choriocapillaris imaging in normal subjects with adaptive optics OCT near the fovea over a very limited field of view, due to limited imaging speed and constraints imposed by adaptive optics . Using OCT phase variance and hardware eye tracking with a second scanning laser ophthalmoscope channel in an OCT system, Braaf et al. demon- strated OCT choriocapillaris angiography of the central fovea from a single normal subject, although the acquisition time per volume was relatively long compared to clinical standards, and multiple volumes were used for averaging . In general, choriocapillaris imaging in vivo using OCT is a relatively unexplored area, and it requires extensive further investigation to relate it to known histological findings in normal and pathological eyes.
In most eyes with CSC, the neurosensory retinal detachment resolves spontaneously within 3 months of duration. However, some patients present with persistent detachment and symptoms after 4 months, suggesting a chronic form of CSC. In these patients, treatment with laser photocoagulation or photodynamic therapy (PDT) is considered. Maruko et al 34 measured the subfoveal choroidalthickness before and after the treatment in 20 eyes of 20 patients with chronic CSC, using SDOCT. In this study, 8 eyes were treated with PDT and 12 eyes with laser photocoagulation. A significant decrease in the choroidalthickness after 4 weeks was found in all eyes treated with PDT (389 ± 106 µm at baseline vs. 330 ± 103 µm after 4 weeks; P < 0.001). Patients treated with laser photocoagulation did not demonstrate a reduction in the choroidalthickness (345 ± 127 µm at baseline vs. 340 ± 124 µm after 4 weeks; P = 0.2). A similar study examining choroidalthickness in 16 patients (16 eyes) with CSC before and after PDT showed a decrease in the subfoveal choroidalthickness after the treatment (from 421 µm [95% CI, 352–489 µm] to 346 µm [95% CI, 278–414]; P = 0.0001). 35 Another investigation also showed that half-dose PDT resulted in thinner subfoveal choroidalthickness (80 µm, 20%) 1 month after treatment, decreased the choroidal vascular hyperpermeability, and maintained the remission for 1 year. 36 These findings may suggest that PDT reduces the choroidal vascular hyperpermeability observed in CSC. 34,36
statistically significant, and the relationship-related variation exceededthe imprecision inherent to the methodology (Table 3).
Different approaches to in vivochoroidal vessel analysis have been suggested in the literature. Choroidal vessel visualization using angiography has shown the segmental vessel structure and their respective watershed zones[28,29]. Watershed zones are highly affected by ageing and ischemia and may offer a more sensitive measure of pathological changes than choroidalthickness change alone . Choroidal OCT imaging offers noninvasive vessel visualization. OCT pixel intensitymeasurementshave been suggested for the analysis of choroidal vessels in AMD eyes . However, this method has been used without determining the border between Sattler’s and Haller’s layers and may be unfeasible when the OCT images are affected by retinal and RPE lesions.
The diffraction of light on holograms is of interest for fun- damental reasons and because of its applications to opti- cal signal processing. 1,2 Although Raman–Nath diffrac- tion on thin holograms is quite useful, Bragg diffraction on thick gratings is probably more interesting because then diffracted light is condensed into one unique mode, provided that the incidence angle and wavelength of the read beam fulfill the so-called Bragg resonance condition. The transition between Raman–Nath and Bragg diffrac- tion regimes has been studied extensively for simple gratings. 3–8 The most commonly used thickness crite- rion is that the grating thickness be larger than some threshold, depending on the grating period and on the light’s wavelength, to be in the Bragg regime where higher diffraction orders become vanishingly small.
proximation which considers flat interfaces. Thus, for typical pavements encountered in practice, like here B = [1.0; 3.0]
GHz in Fig. 4, the difference between the rough and the flat cases in the backscattered echoes amplitudes is significant for the higher frequencies of the bandwidth. Then, the influence of this difference in the GPR estimation process is significant for moderate to high SNR (typically, 25 dB for the thickness).
In the present paper, we deal with the following questions: 1. Given n ∈ R 3 , µ ∈ R and ω ∈ R, is P(n, µ, ω) connected?
2. Given n ∈ R 3 and µ ∈ R, how much is the thickness of the thinnest connected arithmetic discrete plane with normal vector n and translation parameter µ? These questions have already been addressed. In , E. Andres, R. Acharya and C. Sibata characterized separating arithmetic discrete hyperplanes as con- nected set. This result gave a partial answer to the first question. In , Y. G´erard deeper investigated it. He provided an algorithm which determines whether a rational arithmetic discrete hyperplane, that is, with a normal vector n ∈ Z d , is connected. He reduced the (possibly) infinite graph of connectedness of the considered arithmetic discrete hyperplane to a finite one by quotienting it by a subgroup of the lattice of periods of the arithmetic discrete hyperplane. In , V. Brimkov and R. Barneva focused on the second question. They intro- duced explicit formulas for some particular cases and provided an algorithm for the general case. Unfortunately, their algorithm appears to be incorrect .
segmentation was done by an automatic post-processing analysis with FREESURFER and local thicknesses were assessed with CorThiZon . Venous, arterial and CSF velocities were measured from PCMRI with BIOFLOWIMAGE software. ICP and CSF dynamics were extracted form infusion tests. Pearson correlations were calculated between cortical thickness and arterial, venous and CSF velocities, but also ICP and derived indices. Results: Mean cortical thickness is positively correlated with mean ICP (r ¼ 0.48, p ¼ 0.001), ICP pulse amplitude (r ¼ 0.43, p ¼ 0.001), arterial flow (r ¼ 0.44, p ¼ 0.001), aqueductal CSF flow(r ¼ 046, p ¼ 0.001), but negatively correlates with venous flow (r ¼-0.44, p ¼ 0.001) Conclusions: We demonstrate that cortical thickness is correlated with arterial and CSF pulsatility. The causality is more complex since it involves local microcirculation that could not be directly measured. However the association between intracranial pulsatility and gray matter thickness suggests that there is a relationship between vascular alterations at the macroscale level and the pathobiology of cortical atrophy.
In Section 4 we give the limit of the displacements and we show a few relations between some of them. Since some of the a priori estimates established depend on the variable thickness ρ (·) we introduce some weighted Sobolev spaces which allow to obtain the limit fields in a natural way. In Section 5 we pose the problem of elasticity and we specify the assumptions on the applied forces. We show that the choice of the applied forces is reasonable to get the suitable estimate of the total elastic energy, so that the convergence results of the previous sections can be used. In Section 6 we derive the equations satisfied by the limit fields and we prove the strong convergence of the energy. Moreover, we deduce some strong convergences of the fields of the displacement’s decomposition. Finally, in Section 7 we summarize the main results.
Multi-year ice, because of its thickness and strength, represents one of the most significant design and operational concerns for future exploration, development and shipping systems in the Beaufort Sea. The importance of multi-year ice was recognized in the late 1960s and 70s when offshore activities first began in the Beaufort Sea. The three caisson structures that operated in different areas of the Beaufort (Molikpaq, Caisson Retained Island - CRI and Single Steel Drilling Caisson - SSDC) were all designed to withstand impacts with multi-year ice. The Molikpaq did experience impacts with multi-year ice while at the Tarsuit P-45 (1984/85) and Amauligak I-65 (1985/86) sites – interactions that resulted in the highest ice-induced global loads yet measured on a structure. Today, the search for oil and gas is beginning to venture into deeper waters of the Canadian Beaufort Sea, where polar pack ice is not uncommon, while some consideration is now being given to year-round shipping in the general region.