Thickness Asymmetry Research Articles

Does Internal Limiting Membrane Peeling Size Matter?

Purpose: A variety of retinal topographical changes occur after internal limiting membrane (ILM) peeling for macular holes including a movement of the fovea toward the optic nerve. This study was carried out to assess the effect of the extent of ILM-peeled area on these changes and postoperative visual acuity. Methods: Prospective single-center study of a consecutive series of patients undergoing macular hole surgery. Preoperative and postoperative optical coherence tomography images were used to assess a variety of measures of retinal morphology. Transmission electron microscopy of the peeled ILM was used to assess residual retinal and vitreous side debris. The area of the ILM peeled was calculated from intraoperative images. Results: Fifty-six eyes of 56 patients were included. The mean area of ILM peeled was 9.5 mm2 (2.4-28.3 mm2). The mean disc-to-fovea distance (DFD) preoperatively was 3703 μm with a mean reduction of 52 μm postoperatively, representing a change of −1.29% with a wide range of −7.04% to 1.36%. Using stepwise linear regression, ILM-peeled area was significantly associated with a change in DFD ( P < .001), extent of a dissociated optic nerve fiber layer appearance ( P < .001), and postoperative visual acuity ( P = .025). Nasotemporal retinal thickness asymmetry was associated with the minimum linear diameter ( P < .001). Conclusion: The ILM-peeled area has a significant effect on changes in retinal topography and postoperative visual acuity separate from macular hole size. Further study is needed to assess the effect of ILM peeled size on visual function and to guide clinical practice.

Ultrasound Measurements of the Lateral Abdominal Muscle Thicknesses in Girls With Adolescent Idiopathic Scoliosis

Background: It has been suggested that weakness and asymmetry of core stabilizing muscles have an important role in the development of scoliosis and its complications, especially low back pain. However there is insufficient data comparing symmetry and function of these muscles in scoliotic patients with the normal population. Also there are only a few studies assessing the relationship between the degree of spinal deviation and asymmetry of core stabilizing muscles. This study evaluates the thickness, symmetry, and activation of the external oblique (EO), the internal oblique (IO) and the transversus abdominis (TrA) muscles of patients with AIS and compares these data with a group of normal adolescents. Objectives: The objective of this observational study was to know the asymmetry pattern of lateral abdominal muscles at rest and during the abdominal drawing-in maneuver (ADiM) in adolescents with idiopathic scoliosis and to compare it with a group of healthy adolescents. Methods: Twenty healthy adolescents and twenty patients with AIS, aged 10 to 18 years, were included. The thickness of lateral abdominal muscles was measured, using ultrasound, at the end of normal exhalation at rest and during the abdominal drawing-in maneuver (ADiM). Muscular activity was represented as absolute difference and percentage change in the muscle thickness during the ADiM compared with rest. Results: There was no side to side asymmetry in muscle thickness at rest and also during ADiM in two groups. Thickness of right EO [0.39 (0.09) in the AIS group compared to 0.51 (0.12) in the normal group] and left EO [0.38(0.10) in the AIS group compared to 0.50 (0.11) in the normal group] at rest was higher in the normal group (P < 0.05). The activity of right and left EO was higher in AIS group (P < 0.05). There was a positive correlation between the lumbar Cobb’s angle with the right and the right-to-left difference of TrA thickness during the ADiM (P < 0.05). In other words, the more the lumbar Cobb’s angle to the right, the thicker the right TrA relative to the left TrA during the ADiM. Conclusions: The EO muscle was thinner and had higher activity during ADiM in the AIS group. Analysis of our data showed that in the AIS group the higher the lumbar spinal curve to the right, the thicker the right TrA compared to the left TrA.

Predicting the intereye asymmetry in functional and structural damage in glaucoma using automated pupillography.

To predict the intereye asymmetry in functional (mean deviation, MD on visual field, VF) and structural (retinal nerve fibre layer, RNFL and ganglion cell complex, GCC thickness on spectral domain optical coherence tomography, SDOCT) measurements in glaucoma using the automated pupillography parameters. Fifty-nine subjects with a diagnosis of either glaucoma or glaucoma suspect underwent automated pupillography along with VF and SDOCT examinations. Association between pupillography and the absolute intereye difference in MD, RNFL and GCC measurements was evaluated using regression analysis after accounting for the multicollinearity. Univariate regression analysis showed statistically significant associations (p<0.05) between multiple pupillography parameters and the intereye difference in MD, RNFL and GCC thickness measurements. Multivariate regression with less strongly correlated parameters identified intereye difference in amplitude change (Ac) per cent to be the parameter that best predicted the intereye asymmetry in MD (Intereye asymmetry in MD=2.20+1.33*intereye difference in Ac per cent, R2 =0.36), RNFL thickness (3.38+3.55*intereyedifference in Ac per cent, R2 =0.49) and GCC thickness (4.49+2.06* intereye difference in Ac per cent, R2 =0.41). Ability of intereye Ac per cent difference to predict intereye asymmetry in MD, RNFL and GCC thickness was better in patients with angle closure disease (R2 =0.38, 0.79, 0.66, respectively) compared to those with open angles (R2 =0.25, 0.15, 0.16, respectively). Intereye asymmetry in MD, RNFL and GCC thickness measurements was best predicted by the intereye difference in Ac per cent on automated pupillography. The predicting ability was better in patients with angle closure compared to those with open angles.

Bilingualism Influences Structural Indices of Interhemispheric Organization.

Bilingualism represents an interesting model of possible experience-dependent alterations in brain structure. The current study examines whether interhemispheric adaptations in brain structure are associated with bilingualism. Corpus callosum volume and cortical thickness asymmetry across 13 regions of interest (selected to include critical language and bilingual cognitive control areas) were measured in a sample of Spanish-English bilinguals and age- and gender-matched monolingual individuals (N = 39 per group). Cortical thickness asymmetry of the anterior cingulate region differed across groups, with thicker right than left cortex for bilinguals and the reverse for monolinguals. In addition, two adjacent regions of the corpus callosum (mid-anterior and central) had greater volume in bilinguals. The findings suggest that structural indices of interhemispheric organization in a critical cognitive control region are sensitive to variations in language experience.

Marked brain asymmetry with intact cognitive functioning in idiopathic Parkinson’s disease: a longitudinal analysis

Objective: A 71-year-old (MN) with an 11-year history of left onset tremor diagnosed as Parkinson’s disease (PD) completed longitudinal brain magnetic resonance imaging (MRI) and neuropsychological testing. MRI scans showed an asymmetric caudate nucleus (right < left volume). We describe this asymmetry at baseline and the progression over time relative to other subcortical gray, frontal white matter, and cortical gray matter regions of interest. Isolated structural changes are compared to MN’s cognitive profiles. Method: MN completed yearly MRIs and neuropsychological assessments. For comparison, left onset PD (n = 15) and non-PD (n = 43) peers completed the same baseline protocol. All MRI scans were processed with FreeSurfer and the FMRIB Software Library to analyze gray matter structures and frontal fractional anisotropy (FA) metrics. Processing speed, working memory, language, verbal memory, abstract reasoning, visuospatial, and motor functions were examined using reliable change methods. Results: At baseline, MN had striatal volume and frontal lobe thickness asymmetry relative to peers with mild prefrontal white matter FA asymmetry. Over time only MN’s right caudate nucleus showed accelerated atrophy. Cognitively, MN had slowed psychomotor speed and visuospatial-linked deficits with mild visuospatial working memory declines longitudinally. Conclusions: This is a unique report using normative neuroimaging and neuropsychology to describe an individual diagnosed with PD who had striking striatal asymmetry followed secondarily by cortical thickness asymmetry and possible frontal white matter asymmetry. His decline and variability in visual working memory could be linked to ongoing atrophy of his right caudate nucleus.

Optimization-based reduction of contour errors of heavy plates in hot rolling

This paper deals with the reduction of top view contour errors in the hot rolling process. Deviations between the actual plate contour and the desired shape may result from asymmetric rolling conditions caused by, e.g., temperature gradients or non-homogeneous input thickness profiles. Under real rolling conditions these disturbances are hard to predict and hence cannot be compensated in a feedforward approach. Therefore, it seems suitable to apply feedback when contour errors occur. This approach essentially requires a measurement of the plate contour and a mathematical model to predict the plate contour after the roll pass. This model is the basis for an optimization-based approach to determine the necessary adjustment of the rolling mill to reduce contour errors. The optimization problem allows to systematically incorporate constraints on the asymmetry of the output plate thickness. Generally, the compliance of the mill stand is not strictly symmetric and may deteriorate the result of the presented approach. The asymmetric compliance results in an asymmetric deflection of the mill stand which is compensated in an empirical approach utilizing the forces applied during the roll pass. Simulation results and measurements of plates rolled during the normal production demonstrate the effectiveness of the proposed method.

Shock Train/Boundary-Layer Interaction in Rectangular Isolators

Shock trains in rectangular isolators with inflow Mach number of 2.5 and ARs of 3.0 and 6.0 are investigated. Knowledge gained is used to propose a rectangular isolator modification to existing empirical shock train length relations based on circular ducts. A novel, multiplane shadowgraph concept allows simultaneous flow visualization from multiple perspectives. Boundary-layer separation in the low-momentum corner flow regions is observed to occur upstream of the center-flow field by approximately one duct height. The leading edge shock train structure is composed of a hybrid oblique–normal shock front, with oblique shocks spawning from the corner flow separation transforming into a normal shock front near the centerline. Dynamic wall pressure measurements made along the duct major axis allow for direct comparison between the outboard and centerline sensor’s ability to detect incipient unstart, with the outboard sensor detecting the separation-induced pressure rise well ahead of centerline measurements. A modified shock train length relation for rectangular isolators accounts for the effects of potential boundary-layer momentum thickness asymmetry, upstream corner flow separation length scale, and AR magnitude. Improvements in correlation strength are discussed for both ARs, with coefficient of determination and root mean square error improvements on the order of 60% observed for the highest AR tested.

Cortical thickness asymmetries and surgical outcome in neocortical epilepsy

PurposeWe evaluated if cortical thickness measures were associated with surgical outcome in patients with non-lesional neocortical epilepsy. MethodsTwenty-one young patients (age: 2.4–19.7years) with epilepsy of neocortical origin and normal MRI underwent two-stage epilepsy surgery with subdural EEG monitoring. Cortical thickness was measured on presurgical volumetric MRI using the FreeSurfer software. The prognostic value of hemispheric and lobar/regional cortical thickness measures for 1-year and 2-year post-surgical seizure outcome has been analyzed. ResultsAt one-year follow-up, 14 patients (67%) were seizure-free. Hemispheric and frontal lobe cortical thickness showed no/minimal asymmetry in seizure-free patients but thinner cortex ipsilateral to the seizure focus in those with recurrent seizures (p=0.02). More robust differences were found in patients≥6years of age (p=0.006 for frontal asymmetries), whose cortical thickness asymmetries remained prognostic for 2-year post-surgical outcome (p=0.007). By using an optimal cutoff threshold based on a receiver operating characteristic analysis, mean hemispheric asymmetry predicted one-year seizure freedom with 93% sensitivity and 71% specificity in the whole group, and with 100% sensitivity and 92% specificity in patients≥6years of age. ConclusionIn patients with neocortical epilepsy and normal MRI, neocortical thinning in the epileptic hemisphere, particularly in frontal cortex, is associated with poor surgical outcome. Although these results require validation in a larger cohort prospectively, these data suggest that presurgical evaluation of cortical thickness may assist in identification of patients at high risk for surgical failure.

Interface characterization in B-based multilayer mirrors for next generation lithography

The interfaces in La/B4C and LaN/B4C multilayer mirrors designed for near normal incidence reflection of 6.x nm EUV light were investigated by grazing incidence X-ray reflectometry, high-resolution transmission electron microscopy and EUV reflectometry. The thickness and roughness asymmetries of the different interfaces in both studied systems have been identified. A development of interface roughness with an increasing number of bilayers was found by different investigation methods. For near normal incidence, R=51.1% @ λ=6.65nm could be reached with our La/B4C multilayer mirrors, whereas R=58.1% was achieved with LaN/B4C multilayers at the same wavelength.

Asymmetry of fusiform structure in autism spectrum disorder: trajectory and association with symptom severity.

BackgroundWhile asymmetry in the fusiform gyrus (FFG) has been reported in functional and structural studies in typically developing controls (TDC), few studies have examined FFG asymmetry in autism spectrum disorder (ASD) subjects and those studies are limited by small sample sizes, and confounded by cognitive ability or handedness. No previous work has examined FFG surface area or cortical thickness asymmetry in ASD; nor do we understand the trajectory of FFG asymmetry over time. Finally, it is not known how FFG structural asymmetry relates to ASD symptom severity.MethodsIn this study, we examined FFG volume, surface area, and cortical thickness asymmetry, as well as their cross-sectional trajectories in a large sample of right-handed males aged 7 to 25 years with 128 ASD and 127 TDC subjects using general linear models. In addition, we examined the relationship between FFG asymmetry and ASD severity using the Autism Diagnostic Observation Schedule (ADOS) and Gotham autism severity scores.ResultsFindings revealed that while group differences were evident with mean leftward asymmetry in ASD and mean near symmetry in TDC volume and surface area, asymmetry for both groups existed on a spectrum encompassing leftward and rightward asymmetry. In ASD subjects, volume asymmetry was negatively associated with ADOS and autism severity score symptom measures, with a subset of rightward asymmetric patients being most severely affected. We also observed differential trajectory of surface area asymmetry: ASD subjects exhibited a change from leftward asymmetry toward symmetry from age 7 to 25, whereas TDCs exhibited the reverse trend with a change from near symmetry toward leftward symmetry over the observed age range.ConclusionsAbnormalities in FFG structural asymmetry are related to symptom severity in ASD and show differential developmental trajectory compared to TDC. This study is the first to note these findings. These results may have important implications for understanding the role of FFG asymmetry in ASD.Electronic supplementary materialThe online version of this article (doi:10.1186/s13229-016-0089-5) contains supplementary material, which is available to authorized users.

Asymmetry of Retinal Nerve Fiber Layer and Posterior Pole Asymmetry Analysis Parameters of Spectral Domain Optical Coherence Tomography in Children

ABSTRACTPurpose: To determine inter- and intraocular differences in the retinal nerve fiber (RNFL) and posterior pole asymmetry analysis (PPAA) macular thickness parameters in children using spectral domain optical coherence tomography. Method: A prospective, cross-sectional study involving 126 subjects between the age group of 5–15 years received a standardized eye examination including spectral domain optical coherence tomography for retinal nerve fiber layer and macular thickness measurements. Asymmetry was calculated as the difference between the right and left eyes as well as the superior and inferior area of one randomly selected eye for each subject. Normal ranges were established as the 2.5 and the 97.5 percentiles. Correlation between the right and left eyes were assessed by intraclass correlation coefficients. Results: The difference in the average and superior RNFL between the right and the left eye was not statistically significant. The interocular 2.5 and 97.5 percentile limits for RNFL thickness and total PPAA macular thickness were –7.75 to 12.5 microns and –9 to 21 microns, respectively. The 2.5 and 97.5 percentile limits of the intraocular superior-inferior area difference for the RNFL thickness and PPAA macular thickness were –40 to 37 microns and –32 to 38 microns, respectively. A strong correlation for all parameters between the right and the left eye was seen. Conclusion: The normal interocular RNFL and PPAA macular thickness asymmetry should not exceed 12.5 microns and 21 microns, respectively. Similar intraocular limits for superior-inferior asymmetry should not exceed 40 and 38 microns, respectively.

Regional correlations between cortical thickness and surface area asymmetries: A surface-based morphometry study of 250 adults

We report on the patterns of asymmetries of various MRI-derived cortical phenotypes, namely cortical thickness (CT), cortical surface area (CSA), cortical volume (CV) and sulcal depth (SULC), as well as on their cross-relationships. A surface-based approach was designed to obtain cortical asymmetry maps unbiased for inter-hemispheric structural positional misalignment. Accurate vertex-wise asymmetries of CT, CSA, CV, and SULC were so obtained in 250 individuals including 120 left-handers that had been selected from a larger population as having a typical leftward language lateralization. We found no significant effect of handedness on CT, CSA or CV asymmetries, although a trend for a significant difference in the SULC asymmetry of the Rolandic genu was present (leftward in right-handers, rightward in left-handers). At the hemispheric level, we found rightward CT and CSA asymmetries that were not correlated. At the regional level, asymmetry patterns of CT and CSA were marked by a spatial overlap of both concordant and opposite CT and CSA asymmetries. Half of these regions of overlap presented a significant association (positive or negative) between CT and CSA asymmetries. Strikingly, the 3 regions showing positive correlations between CT and CSA asymmetries were those known to exhibit robust asymmetries across methodologies, such as the leftward asymmetrical planum temporale and the rightward asymmetrical superior temporal sulcus and cingulate cortex. This study demonstrates that regional correlations between CT and CSA asymmetries are a characteristic of brain structural organization that could be of significance in the choice of structural markers in studies dealing with the genetic basis of brain lateralization.

Ocular blood flow in glaucoma - the Leuven Eye Study.

Elevated intra-ocular pressure (IOP) has been identified as a major risk factor for glaucoma. Additionally, extensive literature depicts a vascular dysfunction to exist in these patients. However, a large ocular blood flow-oriented trial to integrate these findings in the clinical setting is lacking. This study would likely help to identify which of these vascular data can be used as a clinical tool for screening and disease stratification. Prospective, cross-sectional, case-control hospital-based study. Patients with primary open-angle glaucoma (POAG), normal-tension glaucoma (NTG), ocular hypertension (OHT), glaucoma suspects and healthy volunteers were recruited. In addition to a comprehensive ophthalmological examination, a vascular-oriented questionnaire was completed and ocular blood flow assessment (colour Doppler imaging of retrobulbar vessels, retinal oximetry, dynamic contour tonometry, optical coherent tomography enhanced-depth imaging of the choroid) were performed. Statistical analysis was based on multiple imputation to account for missingness. A total of 614 subjects (291 males) were recruited between March and December 2013 (POAG: 214, NTG: 192; OHT: 27; glaucoma suspect: 41; healthy controls: 140). Glaucoma groups (NTG and POAG) were age and gender matched with the control group (p>0.05). Glaucoma groups were paired in terms of functional and structural parameters (p>0.08). Mean ocular perfusion pressure was higher in the glaucoma groups than in controls (p<0.001). Glaucoma groups had lower retrobulbar velocities, higher retinal venous saturation and choroidal thickness asymmetries when compared to the healthy group, in line with the current literature. The Leuven Eye Study stands as one of the largest clinical trials on ocular blood flow in glaucoma. The creation of this vast database may help integrate the vascular aspects of glaucoma into the clinical practice of glaucoma.

Measurement of cortical thickness asymmetry in carotid occlusive disease.

Despite being considered an important anatomical parameter directly related to neuronal density, cortical thickness is not routinely assessed in studies of the human brain in vivo. This paucity has been largely due to the size and convoluted shape of the human cortex, which has made it difficult to develop automated algorithms that can measure cortical thickness efficiently and reliably. Since the development of such an algorithm by Fischl and Dale in 2000, the number of studies investigating the relationship between cortical thickness and other physiological parameters in the brain has been on the rise. There have been no studies however that have validated cortical asymmetry against known vascular anatomy. To this aim, using high-resolution MRI, we measured cortical thickness and volume in the primary motor (M1) and primary visual (V1) cortex in patients with unilateral, high-grade carotid occlusive disease (n = 29, age = 74 ± 10 years). These regions were selected based on the hypothesis that there will be thinning of the cortical thickness of M1 in the territory supplied by the occluded carotid artery, whereas V1 will show no asymmetry since its blood supply is provided by unaffected posterior arteries. To test for an effect of handedness, cortical thickness and volume were also measured in healthy volunteers (n = 8, age = 37 ± 13 years). In patients, we found thinner cortex in M1 on the occluded side (mean = 2.07 ± 0.19 mm vs 2.15 ± 0.20 mm, p = 0.0008) but no hemispheric difference in V1 (1.80 ± 0.17 mm in occluded vs 1.78 ± 0.16 mm in unoccluded, p = 0.31). Although the mean cortical volume of M1 in the occluded hemisphere was also lower, the difference did not reach statistical significance (p = 0.09). Similarly, in healthy controls, the results showed no hemispheric asymmetry in either cortical thickness or volume in either region (p > 0.1). To test for an orientation bias in the method, the analysis was repeated with images flipped from neurological to radiological orientation. While the algorithm did not yield identical results for the two orientations, the effect did not alter the findings of the study. These results provide a method for within-subject validation of a pathophysiological effect of carotid occlusive disease on the human cortex and warrant further investigation for underlying mechanisms.

Dawn‐dusk asymmetries in rotating magnetospheres: Lessons from modeling Saturn

AbstractSpacecraft measurements reveal perplexing dawn‐dusk asymmetries of field and plasma properties in the magnetospheres of Saturn and Jupiter. Here we describe a previously unrecognized source of dawn‐dusk asymmetry in a rapidly rotating magnetosphere. We analyze two magnetohydrodynamic simulations, focusing on how flows along and across the field vary with local time in Saturn's dayside magnetosphere. As plasma rotates from dawn to noon on a dipolarizing flux tube, it flows away from the equator along the flux tube at roughly half of the sound speed (Cs), the maximum speed at which a bulk plasma can flow along a flux tube into a lower pressure region. As plasma rotates from noon to dusk on a stretching flux tube, the field‐aligned component of its centripetal acceleration decreases and it flows back toward the equator at speeds typically smaller than . Correspondingly, the plasma sheet remains far thicker and the field less stretched in the afternoon than in the morning. Different radial force balance in the morning and afternoon sectors produce asymmetry in the plasma sheet thickness and a net dusk‐to‐dawn flow inside of L = 15 or equivalently, a large‐scale electric field (E) oriented from postnoon to premidnight, as reported from observations. Morning‐afternoon asymmetry analogous to that found at Saturn has been observed at Jupiter, and a noon‐midnight component of E cannot be ruled out.

Association between posterior crossbite, skeletal, and muscle asymmetry: a systematic review.

Of the various malocclusions, unilateral posterior crossbite has often been associated to skeletal and muscular asymmetrical growth and function. To assess, by systematically reviewing the literature, the association between unilateral posterior crossbite (UPCB) and morphological and/or functional asymmetries (i.e. skeletal, masticatory muscle electromyographic (EMG) performance, bite force, muscle thickness, and chewing cycle asymmetries). A literature survey covering the period from January 1965 to June 2015 was performed. Two reviewers extracted the data independently and assessed the quality of the studies. The search strategy resulted in 2184 citations, of which 45 met the inclusion criteria. The scientific and methodological quality of these studies was medium-low, irrespective of the association reported. In several studies, posterior crossbite is reported to be associated to asymmetries in mandibular skeletal growth, EMG activity, and the chewing cycle. Fewer data are available on bite force and masticatory muscle thickness. The relationship between unilateral posterior crossbite and skeletal asymmetry is still unresolved. To date, most of the studies available report a skeletal asymmetric growth. EMG activity of masticatory muscles is different between crossbite and non-crossbite sides. Subjects with UPCB show smaller bite force than non-crossbite subjects. There is no consistency of studies reporting masticatory muscle thickness asymmetry in UPCB subjects. UPCB is associated to an increase in the reverse chewing cycle. The literature available on the subject is of medium-low scientific and methodological quality, irrespective of the association reported. Further investigations with higher sample size, well-defined diagnostic criteria, rigorous scientific methodologies, and long-term control are needed.

The dependence of the LLBL thickness on IMF [formula omitted] and [formula omitted] components

The thickness of the low latitude boundary layer (LLBL) is studied as a function of interplanetary magnetic field (IMF) using the data of THEMIS mission. The data from intersections of LLBL by Themis-A and -C satellites are analyzed. Solar wind parameters are provided by Themis-B satellite located before the bow shock. We use earlier developed method of LLBL thickness determination based on the analysis of the variation of plasma velocity in the layer perpendicular to the magnetopause. The database for the present analysis consists of 109 single satellite LLBL crossings where the values of LLBL thickness are obtained. The time shift of solar wind propagation from the spacecraft performing measurements outside the bow shock to the LLBL is taken into account. We analyze the dependence of LLBL thickness on IMF Bz and By using data of IMF measurements with 3s resolution and produce the 180s averaging of these data. Large scattering of the values of LLBL thickness and the weak dependence on IMF is demonstrated. Dawn–dusk asymmetry of LLBL thickness is not observed. The dependence of LLBL thickness on IMF clock angle is discussed.

Structural asymmetry of the human cerebral cortex: Regional and between-subject variability of surface area, cortical thickness, and local gyrification

Structural asymmetry varies across individuals, brain regions, and metrics of cortical organization. The current study investigated regional differences in asymmetry of cortical surface area, thickness, and local gyrification, and the extent of between-subject variability in these metrics, in a sample of healthy young adults (N=200). Between-subject variability in cortical structure may provide a means to assess the extent of biological flexibility or constraint of brain regions, and we explored the potential influence of this variability on the phenotypic expression of structural asymmetry. The findings demonstrate that structural asymmetries are nearly ubiquitous across the cortex, with differing regional organization for the three cortical metrics. This implies that there are multiple, only partially overlapping, maps of structural asymmetry. The results further indicate that the degree of asymmetry of a brain region can be predicted by the extent of the region's between-subject variability. These findings provide evidence that reduced biological constraint promotes the expression of strong structural asymmetry.

Novel method using 3-dimensional segmentation in spectral domain-optical coherence tomography imaging in the chick reveals defocus-induced regional and time-sensitive asymmetries in the choroidal thickness.

Studies into the mechanisms underlying the active emmetropization process by which neonatal refractive errors are corrected, have described rapid, compensatory changes in the thickness of the choroidal layer in response to imposed optical defocus. While high frequency A-scan ultrasonography, as traditionally used to characterize such changes, offers good resolution of central (on-axis) changes, evidence of local retinal control mechanisms make it imperative that more peripheral, off-axis changes also be tracked. In this study, we used in vivo high resolution spectral domain-optical coherence tomography (SD-OCT) imaging in combination with the Iowa Reference Algorithms for 3-dimensional segmentation, to more fully characterize these changes, both spatially and temporally, in young, 7-day old chicks (n = 15), which were fitted with monocular +15 D defocusing lenses to induce choroidal thickening. With these tools, we were also able to localize the retinal area centralis, which was used as a landmark along with the ocular pectin in standardizing the location of scans and aligning them for subsequent analyses of choroidal thickness (CT) changes across time and between eyes. Values were derived for each of four quadrants, centered on the area centralis, and global CT values were also derived for all eyes. Data were compared with on-axis changes measured using ultrasonography. There were significant on-axis choroidal thickening that was detected after just one day of lens wear (∼190 µm), and regional (quadrant-related) differences in choroidal responses were also found, as well as global thickness changes 1 day after treatment. The ratio of global to on-axis choroidal thicknesses, used as an index of regional variability in responses, was also found to change significantly, reflecting the significant central changes. In summary, we demonstrated in vivo high resolution SD-OCT imaging, used in combination with segmentation algorithms, to be a viable and informative approach for characterizing regional (spatial), time-sensitive changes in CT in small animals such as the chick.

Intraeye retinal nerve fiber layer and macular thickness asymmetry measurements for the discrimination of primary open-angle glaucoma and normal tension glaucoma

PurposeThe aim of this study was to evaluate the diagnostic capability of intraeye retinal nerve fiber layer (RNFL) thickness and macular thickness (MT) asymmetry measurements for the discrimination of normal tension glaucoma (NTG) and primary open-angle glaucoma (POAG) using spectral domain optical coherence tomography (SD-OCT). MethodsA total of 90 subjects were enrolled including 30 consecutive healthy subjects, 30 consecutive subjects with POAG, and 30 consecutive subjects with NTG. RNFL thicknesses around the optic disc as well as MT measurements were taken with circular and radial SD-OCT scans. Intraeye retinal and MT asymmetry were calculated as the absolute difference between superior and inferior hemispheres of the eye using posterior pole asymmetry analysis protocol. Analysis of variance was used for comparison and areas under the receiver operating characteristic (AROC) were obtained for different parameters among the three diagnostic groups. ResultsThere was a significant difference in MT asymmetry for all comparison groups (normal-NTG, p<0.05; normal-POAG, p<0.001; and NTG-POAG, p<0.001). Intraeye retinal nerve fiber thickness asymmetry measurements were not different between the groups (normal-NTG, p<0.187; normal-POAG, p<0.056; and NTG-POAG, p<0.837). The area under ROC curves exceeded 0.800 for all the studied parameters, including the MT asymmetry except for intraeye RNFL thickness asymmetry which had the lowest AROC as well as the least sensitivity for identifying subjects with NTG from normal (AROC=0.626, sensitivity=30%); POAG from normal (AROC=0.644, sensitivity=37%) and NTG from POAG (AROC=0.533, sensitivity=13%). ConclusionThe intraeye MT asymmetry holds significant potential as a distinguishing parameter for NTG and POAG.