Centroid Of Area Research Articles

Going the distance: Associations between adverse birth outcomes and obstetric provider distances for adolescent pregnancies in South Carolina.

Distances to obstetric care providers are a persistent concern, especially for rural pregnant adolescents. Births to adolescents are disproportionately affected by adverse birth outcomes (ABOs), yet little is known regarding how driving distances may impact ABOs. This study examines the association between driving distances to obstetric providers and ABOs among adolescent mothers in South Carolina. This retrospective cross-sectional study derived ZIP Code-level birth statistics from mothers aged 10-19 in South Carolina using 2013-2017 statewide birth certificate data. ABOs included preterm birth and/or low birthweight. Provider distance was calculated between an obstetric provider's ZIP Code tabulated area (ZCTA) centroid and a maternal resident's ZCTA centroid. Descriptive statistics and weighted generalized linear regression were conducted. Mean provider distances to obstetric providers were similar between urban (11.76 miles) and rural adolescent mothers (12.04 miles). An increase in provider distance, on average, was associated with a decrease in ABO rates (-0.79, p= .0038); however, rural-urban differences were found. Living in a rural ZCTA was associated with a decrease in ABOs (4.94%, p = .0043). Urban ZCTAs showed a U-shaped association with provider distance, with ABO rates decreasing until approximately 17 miles away from a provider and then increasing. Rural adolescent mothers with greater distance to providers had lower ABO rates, while, in urban ZCTAs, provider distance over 17 miles was associated with higher ABO rates. Understanding what mitigates the effects of driving distance on ABOs in rural South Carolina would help inform future policy planning in underserved communities.

Influence of the Spatial Pressure Distribution of Breaking Wave Loading on the Dynamic Response of Wolf Rock Lighthouse

The survivability analysis of offshore rock lighthouses requires several assumptions of the pressure distribution due to the breaking wave loading (Raby et al. (2019), Antonini et al. (2019). Due to the peculiar bathymetries and topographies of rock pinnacles, there is no dedicated formula to properly quantify the loads induced by the breaking waves on offshore rock lighthouses. Wienke’s formula (Wienke and Oumeraci (2005) was used in this study to estimate the loads, even though it was not derived for breaking waves on offshore rock lighthouses, but rather for the breaking wave loading on offshore monopiles. However, a thorough sensitivity analysis of the effects of the assumed pressure distribution has never been performed. In this paper, by means of the Wolf Rock lighthouse distinct element model, we quantified the influence of the pressure distributions on the dynamic response of the lighthouse structure. Different pressure distributions were tested, while keeping the initial wave impact area and pressure integrated force unchanged, in order to quantify the effect of different pressure distribution patterns. The pressure distributions considered in this paper showed subtle differences in the overall dynamic structure responses; however, pressure distribution #3, based on published experimental data such as Tanimoto et al. (1986) and Zhou et al. (1991) gave the largest displacements. This scenario has a triangular pressure distribution with a peak at the centroid of the impact area, which then linearly decreases to zero at the top and bottom boundaries of the impact area. The azimuthal horizontal distribution was adopted from Wienke and Oumeraci’s work (2005). The main findings of this study will be of interest not only for the assessment of rock lighthouses but also for all the cylindrical structures built on rock pinnacles or rocky coastlines (with steep foreshore slopes) and exposed to harsh breaking wave loading.

Spatial regression approach to estimate synthetic unit hydrograph by geomorphic characteristics of watersheds in arid regions

Rainfall-runoff relationship in arid regions is unique and challenging to study. Studies for bridging the hydro-meteorological knowledge gap for planning, designing and managing water resources is therefore vitally important. The objective of this study is to develop a method for estimating unit hydrograph at reasonably finer time resolutions (10-min and 1-h) which can be easily adaptable by practitioners at sub-catchment levels, especially when the focus area is ungauged. Observed wadi-flow at 5-min interval and tipping bucket rainfall measurements at 1-min interval were obtained to cover 10 major watersheds in Oman. The deconvolution method was applied to derive the unit hydrographs (UHs) from wadi-flow and excess rainfall. Key catchment characteristics such as the watershed area, length of the main wadi and the length to the centroid of the catchment area were derived from digital elevation model (DEM) data. The whole study area was then divided into 515 sub-catchments with various shapes and sizes. A strong relationship was found between the wadi length and the length to the centroid of the catchment area (R2>0.89). This relationship was then adopted to simplify the classical Snyder method to determine UHs. Moreover, several parameters of the Snyder method were calibrated to the arid environment by matching the peak-flow, lag-time and three time-widths (75%, 50% and 30% of the peak-flow) of 10-min and 1-h UHs with physical characteristics of the watersheds. All developed relationships were validated with independent rainfall and wadi-flow events. Results indicate that the calibrated parameters in these arid watersheds are quite distinct from those suggested for other regions of the world. A marked difference was found between the 10-min UHs estimated by the S-hydrograph method and the deconvolution method. Therefore, it is concluded that a method depends on natural hydro-meteorological conditions would be more practical in arid region. The proposed methodology can be used for water resources management in arid regions having similar climate and geographical settings.

Static stiffness of rigid foundation resting on elastic half-space using a Galerkin boundary element method

In this work, a simple and effective numerical model is proposed for studying flexible and rigid foundations in bilateral and frictionless contact with a three-dimensional elastic half-space. For this purpose, a Galerkin Boundary Element Method for the substrate is introduced, and both surface vertical displacements and half-space tractions are discretized by means of a piecewise constant function. The work focuses on a transversely isotropic substrate having the plane of isotropy parallel to the half-space boundary, hence the relationship between vertical displacements and half-space reactions is given by Michell solution, reducing to Boussinesq solution for an isotropic half-space. Several numerical tests are performed for showing the effectiveness of the model, on one hand by determining vertical displacements of flexible rectangular foundations subjected to vertical pressures, on the other hand by accurately determining the translational and rotational stiffness of rigid rectangular and L-shaped foundations. Particular attention is given to the determination of the center of stiffness in case of unsymmetrical foundations, since it turns out to be not coincident with foundation area centroid.

Adduction-Induced Strain on the Optic Nerve in Primary Open Angle Glaucoma at Normal Intraocular Pressure

ABSTRACT Purpose/Aim The optic nerve (ON) becomes taut during adduction beyond ~26° in healthy people and patients with primary open angle glaucoma (POAG), but only retracts the globe in POAG. We used magnetic resonance imaging (MRI) to investigate this difference. Materials and Methods MRI was obtained in 2-mm quasi-coronal planes in central gaze, and smaller (~23-25°) and larger (~30-31°) adduction and abduction in 21 controls and 12 POAG subjects whose intraocular pressure never exceeded 21 mmHg. ON cross-sections were analyzed from the globe to 10 mm posteriorly. Area centroids were used to calculate ON path lengths and changes in cross-sections to calculate elongation assuming volume conservation. Results For both groups, ON path was nearly straight (<102.5% of minimum path) in smaller adduction, with minimal further straightening in larger adduction. ON length was redundant in abduction, exceeding 103% of minimum path for both groups. For normals, the ON elongated 0.4 ± 0.5 mm from central gaze to smaller adduction, and 0.4 ± 0.5 mm further from smaller to larger adduction. For POAG subjects, the ON did not elongate on average from central gaze to smaller adduction and only 0.2 ± 0.4 mm from smaller to larger adduction (P = .045 vs normals). Both groups demonstrated minimal ON elongation not exceeding 0.25 mm from central gaze to smaller and larger abduction. The globe retracted significantly more during large adduction in POAG subjects than normals (0.6 ± 0.7 mm vs 0.2 ± 0.5 mm, P = .027), without appreciable retraction in abduction. For each mm increase in globe axial length, ON elongation in large adduction similarly increased by 0.2 mm in each group. Conclusions The normal ON stretches to absorb force and avert globe retraction in adduction. In POAG with mild to severe visual field loss, the relatively inelastic ON tethers and retracts the globe during adduction beyond ~26°, transfering stress to the optic disc that could contribute to progressive neuropathy during repeated eye movements.

Detection of transformer winding faults using FRA and image features

Frequency response analysis (FRA) is a widely used approach for detecting winding faults in a transformer. Appropriate and quantitative FRA features will help to improve the accuracy of fault diagnosis. In this study, a novel FRA interpretation including new image features is proposed based on the image processing technique. First, winding faults of different windings are simulated in a test autotransformer and the FRA curves are measured under various faults. Then frequency region division method and image processing technique are first applied to the measured FRA curves. The area ratio and centroid deviation in different frequency regions are calculated through a novel algorithm. Finally, the image features are used as the inputs to support vector machine model. Additionally, three different parametric optimisation algorithm are compared during the training process. The results show that the particle swarm optimisation and image feature exhibit best performance for identifying winding faults.

The Effect of Axial Length on Extraocular Muscle Leverage

Magnetic resonance imaging was used to determine the effect of axial length (AL) on globe rotational axis and horizontal extraocular muscle leverage during horizontal duction. Prospective observational case series. At a single academic center, 36 orthophoric adults with a wide range of ALs underwent high-resolution axial orbital magnetic resonance imaging in target-controlled adduction and abduction. ALs were measured in planes containing maximum globe cross-sections. Area centroids were calculated to determine globe centers. Rotational axes in orbital coordinates were calculated from displacements of lens centers and globe-optic nerve attachments. Lever arms were calculated as distances between published extraocular muscle insertions and rotational axes. ALs averaged 26.3 ± 0.3mm (standard error [range 21.5-33.4mm]). Rotational axes from adduction to abduction averaged 1.1 ± 0.2mm medial and 1.1 ± 0.2mm anterior to the globe's geometric center in adduction. Linear regression demonstrated no significant correlation between AL and rotational axis horizontal (R2= 0.06) or anteroposterior (R2= 0.07) position. Medial rectus (MR) lever arms averaged 12.0 ± 0.2mm and lateral rectus (LR) lever arms averaged 12.8 ± 0.2mm. Both MR (R2= 0.24, P < .001) and LR (R2= 0.32, P < .001) lever arms significantly increased by about 0.3mm per 1.0-mm of increased AL, with a corresponding reduction in predicted per-millimeter effect of surgical repositioning of their insertions. Regardless of AL, the globe rotates about a point nasal and anterior to its geometric center, giving the LR more leverage than the MR. This eccentricity may diminish the effect of tendon repositioning in moderate to highly myopic patients, with reductions in per-mill imeter dose/response predicted with longer AL.

The Impact of Scaphoid Malunion on Radioscaphoid Joint Contact: A Computational Analysis

The clinical relevance of scaphoid malunion is controversial because the biomechanical sequelae remain poorly understood. In this computational study, the effect of increasing scaphoid malunion on radioscaphoid joint contact was assessed. Six computational wrist models of active wrist flexion-extension were used to examine 6 scaphoid malunions of varying severities. The malunions were computationally created using 3-dimensional imaging software. Each scaphoid was shortened at the waist by 2 mm to simulate fracture comminution and the distal pole was angulated volarly from 15° to 55° in 10° intervals to create a total of 6 scaphoid malunion models per specimen. Each malunion model was then assessed at 3 wrist positions: neutral, 40° flexion, and 40° extension. The radioscaphoid contact area, as well as the contact centroid, was calculated. There was a statistically significant association between malunion severity and a wider area of contact at the radiocar: pal joint. The centroid of this radioscaphoid contact area also moved in an ulnar direction for all tested wrist positions. In the extended wrist position, the centroid also moved volarly. In this computational model, the amount of radioscaphoid joint contact was significantly increased with progressive scaphoid malunion severity. Furthermore, the position of the contact centroid had a significant change in position in the ulnar direction in all wrist positions with increasing scaphoid malunion. The clinical importance of this contact is yet to be elucidated, but this computational model serves as a basis for understanding the biomechanical consequences of scaphoid humpback deformities. This study provides a computational analysis examining changes at the radioscaphoid joint that may occur within the wrist with the scaphoid malunited.

Geographic disparities in residential proximity to colorectal and cervical cancer care providers.

Persistent rural-urban disparities for colorectal and cervical cancers raise concerns regarding access to treatment providers. To the authors knowledge, little is known regarding rural-urban differences in residential proximity to cancer specialists. Using the 2018 Physician Compare data concerning physician practice locations and the 2012 to 2016 American Community Survey, the current study estimated the driving distance from each residential zip code tabulation area (ZCTA) centroid to the nearest cancer provider of the following medical specialties involved in treating patients with colorectal and cervical cancer: medical oncology, radiation oncology, surgical oncology, general surgery, gynecological oncology, and colorectal surgery. Using population-weighted multivariable logistic regression, the authors analyzed the associations between ZCTA-level characteristics and driving distances >60 miles to each type of specialist. ZCTA-level residential rurality was defined using rural-urban commuting area codes. Nearly 1 in 5 rural Americans lives >60 miles from a medical oncologist. Rural-urban differences in travel distances to the nearest cancer care provider(s) increased substantially for cancer surgeons; greater than one-half of rural residents were required to travel 60 miles to reach a gynecological oncologist, compared with 8 miles for their urban counterparts. Individuals residing within ZCTAs with a higher poverty rate, those of American Indian/Alaska Native ethnicity, and/or were located in the South and West regions were more likely than their counterparts to be >60 miles away from any of the aforementioned providers. The substantial travel distances required for rural, low-income residents to reach a cancer specialist should prompt a policy action to increase access to specialized cancer care for millions of rural residents.

The application of fuzzy logic for profit optimization to contractor project cash flow

Profit has become the main goal for a contractor without neglecting other aspects in the content of contract. According to previous empirical studies, profit has been optimized. However, it was optimized not as an output variable. Therefore, in this study we were going to try to position profit as an output variable using Fuzzy logic. The research aimed to: 1) describe cash in and cash out to prepare empirical Project Cash Flow (PCF) statement, 2) develop Fuzzy Mamdani set model on PCF 3) formulate manual method and Fuzzy Mamdani computational programming on PCF, 4) validate the results of manual simulation using computation, and 5) make profit which can be simulated. The results of the study were: 1). Fuzzy Mamdani set model with 4 input variables (%), those were: Direct Cost (7-75), Indirect Cost (2-25), Informal cost (1-15) and Progress (0-100) and single output which was profit (0 - 10); 2). The manual method consisted of 4 stages: (1) creating a fuzzy set of 4 input variables and 1 output variable, (2) making the Application Function Implications based on 2 rules, (3) Composing all output variables with the MAX operation, and (4) Defuzzification using the method of centroid of area, 3). computational way with indicators: Trapezoid membership function, two-type linguistic set (minimum - maximum) and (slow - fast), MISO (Multiple Input Single Output) implication functions, “MAX - DOT” operation system, fuzzy rules (if … and … then) = 16 rules, 4). The output of the manual method and computational method resulted the same profit of 4.46, so it was declared valid, and 5). The simulation revealed that minimum profit can be made if the cash out allocation and progress on input variables are not balanced and in contrast, we will obtain maximum profit if the allocation of cash out and progress are balanced with input variable.

How far from home do crashes occur? A network based analysis

This paper investigates the proximity of crashes to the residential locations of the crash occupants. To this end, two years of crash data was disaggregated by the crash occupants’ ZIP codes for a study area in Southwest Florida in order to calculate the roadway network distances between their residential ZIP code area centroids (origins) and crash spots (destinations). These distances are then used to create multiple O-D vectors, so that several different groups can be analyzed controlling for non-motorist types (e.g. pedestrians, cyclists), rural vs. urban origin ZIP codes, different levels of crash severity, DUI involvement, and different age groups. Then, the best-fitting statistical distributions were identified for each group to assess the proximity of crash spots to the residences of crash occupants. Finally, a selection model was implemented to identify the effects of several factors on the distance between the crash spots and the residence locations. Results indicate clear differences in crash involvement among the groups with respect to varying urban densities, people’s ages and modes of travel. These findings can help in the development of more accurate crash prediction methods, as most current approaches only implement variables associated with traffic and roadway geometry.

Imaging of the Mouse Lymphatic Sinus during Early Stage Lymph Node Metastasis Using Intranodal Lymphangiography with X-ray Micro-computed Tomography.

Lymph node (LN) metastasis is detected prior to distant metastasis in many types of cancer. Detecting early stage LN metastasis can improve treatment outcomes. However, there are few clinical imaging modalities capable of diagnosing metastatic LNs of clinical N0 status (i.e., before their volume increases) with high precision. Here, we report a new method for diagnosing metastatic LNs of clinical N0 status in a mouse model of LN metastasis. The method involved using intranodal lymphangiography with x-ray micro-computed tomography (micro-CT). Contrast agent was injected into an upstream LN to deliver it to a downstream LN, which was then removed and analyzed by micro-CT. We found that using an intranodal injection rate of 10-60μl/min filled the lymphatic sinus of the downstream LN with contrast agent, although the accumulation of contrast agent in the upstream LN increased with a faster injection rate. Furthermore, breast cancer cells growing in the lymphatic sinus of the downstream LN (which was of clinical N0 status) impeded the flow of contrast agent from the upstream LN, resulting in areas deficient of contrast agent in the metastatic downstream LN. The formation of defect areas in the downstream LN manifested as a difference in position between the centroid of the entire LN area and the centroid of the region that filled with contrast agent. The present study indicates that intranodal lymphangiography with micro-CT has the potential to be used as a new method for diagnosing metastatic LNs of clinical N0 status.

Pre-hospital Transport Times and Outcomes After Different Reperfusion Strategies for ST-Elevation Myocardial Infarction

This study evaluated prehospital transport times and clinical outcomes after different reperfusion strategies for ST-elevation myocardial infarction in a real-world setting. We consecutively enrolled 27,205 patients who underwent percutaneous coronary intervention (PCI) for ST-elevation myocardial infarction in Michigan from 2010 to 2016. Primary PCI was performed in 25,927 patients (95%), whereas 1,278 (5%) were treated with a pharmacoinvasive strategy. The overall use of a pharmacoinvasive strategy decreased during the study period (p <0.001). Prehospital transport times were estimated by using the Google Maps API from the centroid of each home zip code tabulation area to the zip code tabulation area for the nearest hospital with PCI capability. The estimated prehospital transport time predicted the choice of reperfusion strategy (p <0.001). Primary PCI was used in 97% of the patients living within 1 hour from a hospital with PCI capability compared with 48% with estimated transport times >1 hour. Bleeding and mortality rates were similar for patients treated with primary PCI or a pharmacoinvasive strategy (odds ratio 0.832, 95% confidence interval 0.649 to 1.067, p = 0.147). In conclusion, almost all patients in Michigan had timely access to a hospital with PCI capability and received treatment with primary PCI. The authors declare no conflicts of interests.

Spatio-temporal analysis of the geographical centroids for three major crops in China from 1949 to 2014

Spatial distribution changes in major crops can reveal important information about cropping systems. Here, a new centroid method that applies physics and mathematics to spatial pattern analysis in agriculture is proposed to quantitatively describe the historical centroids of rice, maize and wheat in China from 1949 to 2014. The geographical centroids of the rice area moved 413.39 km in a 34.32° northeasterly (latitude 3.08°N, longitude 2.10°E) direction at a speed of 6.36 km/year from central Hunan province to Hubei province, while the geographical centroids of rice production moved 509.26 km in the direction of 45.44° northeasterly (latitude 3.22°N, longitude 3.27°E) at a speed of 7.83 km/year from central Hunan province to Henan province. The geographical centroids of the maize area and production moved 307.15 km in the direction of 34.33° northeasterly (latitude 2.29°N, longitude 1.56°E) and 308.16 km in the direction of 30.79° northeasterly (latitude 2.39°N, longitude 1.42°E), respectively. However, the geographical centroids of the wheat area and production were randomly distributed along the border of Shanxi and Henan provinces. We divided the wheat into spring wheat and winter wheat and found that the geographical centroids of the spring wheat area and production were distributed within Inner Mongolia, while the geographical centroids of winter wheat were distributed in Shanxi and Henan provinces. We found that the hotspots of crop cultivation area and production do not always change concordantly at a larger, regional scale, suggesting that the changing amplitude and rate of each crops’ yield differ between different regions in China. Thus, relevant adaptation measures should be taken at a regional level to prevent production damage in those with increasing area but decreasing production.

Hours worked of the self‐employed and agglomeration

AbstractThis paper investigates the causal effects of agglomeration on hours worked by the self‐employed. Urbanization and localization are instrumented using the minimum distance from the work Public Use Microdata Area centroid to the United States’ coastlines and estimated industry shares in 1930. The 2SLS results demonstrate that urbanization decreases, and localization increases, hours worked of the self‐employed, respectively. These results are mainly from outsourcing and competition, whereas sorting, simultaneity, and agglomeration wage effect are less likely to be influential. Additionally, only small business owners perceive the pressures of competition in localization economies. The young unincorporated self‐employed are more likely to be affected by peer competitors, whereas the elder unincorporated perceive more pressures from large firms.

FNDSB: A fuzzy-neuro decision support system for back pain diagnosis

Back pain is a common pain felt in the back. In the world, it is the fifth common reason for physician visits and in the U.S. about 90% of human adults have back pain at some time in their life. In this paper, we proposed a decision support system for intelligent diagnosis of back pain using a fuzzy-neuro technique to manage the fuzzy concepts. It is also provide an intelligent decision support platform that can assist physicians to diagnose and produce accurate medical advices. The proposed system consists of a user interface that receive symptoms and produce accurate diagnosis with its severity, a fuzzy inference system which contains the strategies of reasoning process based on fuzzification and defuzzification techniques, a fuzzy-neuro system that composed of neural network with fuzzy logic concepts, and a knowledge base which collects of linguistic fuzzy rules. The FNDSB describe knowledge acquisition and representation methods, a way of production linguistic fuzzy rules organization, fuzzification and defuzzification of clinical parameters as input and output values using a Triangular Membership Function (TMF) and Centroid of Area (CoA) techniques respectively. The FNDSB was evaluated using a case study of 10 patients from Al-diwaniyah teaching hospital. According to the evaluation results the system performance around 83.6% efficiency in producing accurate back pain diagnosis.

3D laser scanning in conjunction with surface texturing to evaluate shift and reduction of the tibiofemoral contact area after meniscectomy

Meniscectomy significantly change the kinematics of the knee joint by reducing the contact area between femoral condyles and the tibial plateau, but the shift in the contact area has been poorly described. The aim of our investigation was to measure the shift of the tibiofemoral contact area occurring after meniscectomy.We used laser scans combined to surface texturing for measuring the 3D position and area of the femoral and tibial surfaces involved in the joint. In particular, natural condyles (porcine model) were analysed and the reverse engineering approach was used for the interpretation of the results from compression tests and local force measurements in conjunction with staining techniques.The results suggested that laser scans combined to surface texturing may be considered as a powerful tool to investigate the stained contours of the contact area. Beside the largely documented reduction of contact area and local pressure increase, a shift of the centroid of the contact area toward the intercondylar notch was measured after meniscectomy.As a consequence of the contact area shift and pressure increase, cartilage degeneration close to the intercondylar notch may occur.

Multiple Hidden Markov Model Post Processed with Support Vector Machine to Recognize English Handwritten Numerals

This paper presents rotation and size invariant English numerals recognition system with, competitive recognition rate. The novelty of this paper is the introduction of two unique methods of feature extraction namely Pixel Moment of Inertia (PMI) and Delta Distance Coding (DDC). The proposed Multiple Hidden Markov Model (MHMM) is a two tier model to neutralize the effect of two very frequent writing styles of numerals ‘4’ and ‘7’ on their recognition rates. The novelty of PMI is that it finds moment of all the pixels of a specified zone about the central pixel and not about geometrical centroid of image area. In this paper, PMI has been observed to have an upper hand over centroidal MI. DDC is a new technique of curvature coding, based on distance from a reference level and is similar to the logic behind Delta modulation scheme in Digital Communications. Thus, the current paper correlates two digital domains namely, Digital Image Processing and Digital Communications. Support Vector Machine differentiates two close output classes obtained from classification with MHMM. The overall recognition accuracy rate of 99.17% has been achieved based on MNIST database.

A High-Precision US-Guided Robot-Assisted HIFU Treatment System for Breast Cancer

Abstract Breast cancer is the most commonly diagnosed cancer in women. A strong treatment candidate is high-intensity focused ultrasound (HIFU), a non-invasive therapeutic method that has already demonstrated its promise. To improve the precision and lower the cost of HIFU treatment, our group has developed an ultrasound (US)-guided, five-degree-of-freedom (DOF), robot-assisted HIFU system. We constructed a fully functional prototype enabling easy three-dimensional (3D) US image reconstruction, target segmentation, treatment path generation, and automatic HIFU irradiation. The position was calibrated using a wire phantom and the coagulated area was assessed on heterogeneous tissue phantoms. Under the US guidance, the centroids of the HIFU-ablated area deviated by less than 2 mm from the planned treatment region. The overshoot around the planned region was well below the tolerance of clinical usage. Our system is considered to be sufficiently accurate for breast cancer treatment.

Optic Nerve Sheath Tethering in Adduction Occurs in Esotropia and Hypertropia, But Not in Exotropia.

PurposeRepetitive strain to the optic nerve (ON) due to tethering in adduction has been recently proposed as an intraocular pressure-independent mechanism of optic neuropathy in primary open-angle glaucoma. Since strabismus may alter adduction, we investigated whether gaze-related ON straightening and associated globe translation differ in horizontal and vertical strabismus.MethodsHigh-resolution orbital magnetic resonance imaging was obtained in 2-mm thick quasi-coronal planes using surface coils in 25 subjects (49 orbits) with esotropia (ET, 19 ± 3.6Δ SEM), 11 (15 orbits) with exotropia (XT, 33.7 ± 7.3Δ), 7 (12 orbits) with hypertropia (HT, 14.6 ± 3.2Δ), and 31 normal controls (62 orbits) in target-controlled central gaze, and in maximum attainable abduction and adduction. Area centroids were used to determine ON path sinuosity and globe positions.ResultsAdduction angles achieved in ET (30.6° ± 0.9°) and HT (27.2° ± 2.3°) did not significantly differ from normal (28.3° ± 0.7°), but significantly less adduction was achieved in XT (19.0° ± 2.5°, P = 0.005). ON sheath tethering in adduction occurred in ET and HT similarly to normal, but did not in XT. The globe translated significantly less than normal, nasally in adduction in XT and temporally in abduction in ET and HT (P < 0.02, for all). Globe retraction did not occur during abduction or adduction in any group.ConclusionsSimilar to normal subjects, the ON and sheath become tethered without globe retraction in ET and HT. In XT, adduction tethering does not occur, possibly due to limited adduction angle. Thus, therapeutic limitation of adduction could be considered as a possible treatment for ON sheath tethering.