Volume change of the ocular lens during accommodation

2007 ◽  
Vol 293 (2) ◽  
pp. C797-C804 ◽  
Author(s):  
R. Gerometta ◽  
A. C. Zamudio ◽  
D. P. Escobar ◽  
O. A. Candia
Keyword(s):  
Structural Parameters ◽  
Center Of Mass ◽  
Physiological Solution ◽  
Volume Determination ◽  
Cross Sectional ◽  
Lens Fibers ◽  
Human Lenses ◽  
Lens Surface ◽  
Shape Changes ◽  
Anterior Posterior

During accommodation, mammalian lenses change shape from a rounder configuration (near focusing) to a flatter one (distance focusing). Thus the lens must have the capacity to change its volume, capsular surface area, or both. Because lens topology is similar to a torus, we developed an approach that allows volume determination from the lens cross-sectional area (CSA). The CSA was obtained from photographs taken perpendicularly to the lenticular anterior-posterior (A-P) axis and computed with software. We calculated the volume of isolated bovine lenses in conditions simulating accommodation by forcing shape changes with a custom-built stretching device in which the ciliary body-zonulae-lens complex (CB-Z-L) was placed. Two measurements were taken (CSA and center of mass) to calculate volume. Mechanically stretching the CB-Z-L increased the equatorial length and decreased the A-P length, CSA, and lens volume. The control parameters were restored when the lenses were stretched and relaxed in an aqueous physiological solution, but not when submerged in oil, a condition with which fluid leaves the lens and does not reenter. This suggests that changes in lens CSA previously observed in humans could have resulted from fluid movement out of the lens. Thus accommodation may involve changes not only in capsular surface but also in volume. Furthermore, we calculated theoretical volume changes during accommodation in models of human lenses using published structural parameters. In conclusion, we suggest that impediments to fluid flow between the aquaporin-rich lens fibers and the lens surface could contribute to the aging-related loss of accommodative power.

scholarly journals The patellofemoral morphology and the normal predicted value of tibial tuberosity-trochlear groove distance in the Chinese population

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Zhe Li ◽  
Guanzhi Liu ◽  
Run Tian ◽  
Ning Kong ◽  
Yue Li ◽  
...  
Keyword(s):  
Individual Differences ◽  
Chinese Population ◽  
Pearson Correlation ◽  
Three Dimensional ◽  
Correlation Coefficients ◽  
Tibial Tuberosity ◽  
Trochlear Groove ◽  
Lasso Regression ◽  
Cross Sectional ◽  
Anterior Posterior

Abstract Background Our objective was to obtain normal patellofemoral measurements to analyse sex and individual differences. In addition, the absolute values and indices of tibial tuberosity-trochlear groove (TT-TG) distances are still controversial in clinical application. A better method to enable precise prediction is still needed. Methods Seventy-eight knees of 78 participants without knee pathologies were included in this cross-sectional study. A CT scan was conducted for all participants and three-dimensional knee models were constructed using Mimics and SolidWorks software. We measured and analysed 19 parameters including the TT-TG distance and dimensions and shapes of the patella, femur, tibia, and trochlea. LASSO regression was used to predict the normal TT-TG distances. Results The dimensional parameters, TT-TG distance, and femoral aspect ratio of the men were significantly larger than those of women (all p values < 0.05). However, after controlling for the bias from age, height, and weight, there were no significant differences in TT-TG distances and anterior-posterior dimensions between the sexes (all p values > 0.05). The Pearson correlation coefficients between the anterior femoral offset and other indexes were consistently below 0.3, indicating no relationship or a weak relationship. Similar results were observed for the sulcus angle and the Wiberg index. Using LASSO regression, we obtained four parameters to predict the TT-TG distance (R2 = 0.5612, p < 0.01) to achieve the optimal accuracy and convenience. Conclusions Normative data of patellofemoral morphology were provided for the Chinese population. The anterior-posterior dimensions of the women were thicker than those of men for the same medial-lateral dimensions. More attention should be paid to not only sex differences but also individual differences, especially the anterior condyle and trochlea. In addition, this study provided a new method to predict TT-TG distances accurately.

Motion Simulation of Key Components in a Package Machine

2012 ◽  
Vol 557-559 ◽  
pp. 2303-2306
Author(s):  
Shu Bin Kan
Keyword(s):  
Structural Parameters ◽  
Center Of Mass ◽  
Motion Simulation ◽  
Software Environment ◽  
Optimization Result ◽  
Adams Software ◽  
Motion Characteristic ◽  
The Moment ◽  
Selection Of

The motion characteristic of key components is a decisional factor to the working reliability and stability of a package machine. In this paper, the motion simulation of a key component is carried out in the ADAMS software environment. By analysis of the force, variance of the center-of-mass and the moment of the component, the mutation point in the motion is found, and then the structure is optimized by selection of different structural parameters. The optimization result shows a significant improvement for the reliability and stability of the whole machine.

scholarly journals Analysis of Corneal Spherical Aberrations in Chinese Bilateral Ectopia Lentis Patients

2021 ◽  
Vol 8 ◽  
Author(s):  
Jiahui Chen ◽  
Yating Tang ◽  
Qinghe Jing ◽  
Yi Lu ◽  
Yongxiang Jiang
Keyword(s):  
Spherical Aberration ◽  
Linear Regression Analysis ◽  
Multiple Linear Regression Analysis ◽  
Cross Sectional Study ◽  
Cross Sectional ◽  
Individual Measurement ◽  
Ectopia Lentis ◽  
Corneal Asphericity ◽  
Optical Zone ◽  
Anterior Posterior

Purpose: To analyze the anterior, posterior, and total corneal spherical aberrations (ASA, PSA, and TSA) in patients with Chinese bilateral ectopia lentis (EL).Methods: A cross-sectional study was conducted to evaluate corneal spherical aberration (CSA) using a Pentacam system at the 6-mm optical zone. Axial length, keratometry, astigmatism, and corneal asphericity were also determined.Results: This study included 247 patients (420 eyes) with a mean age of 18.1 years. The values of ASA, PSA, and TSA were 0.136 ± 0.100 μm, −0.118 ± 0.030 μm, and 0.095 ± 0.095 μm, respectively. In the EL patients with Marfan syndrome (MFS), ASA and TSA were significantly lower than in the non-MFS patients (0.126 ± 0.094 μm vs. 0.155 ± 0.107 μm, P = 0.004 for ASA; 0.085 ± 0.091 μm vs. 0.114 ± 0.099 μm, P = 0.003 for TSA), whereas PSA was not significantly different (P = 0.061). The values of ASA and TSA were significantly higher in the patients with EL aged ≥ 40 years old than in younger patients, whereas ASA and PSA were lower in patients aged &lt;10 years old than in older patients (all P &lt; 0.05). In the multiple linear regression analysis, age, keratometry, astigmatism, anterior asphericity, higher-order aberration (HOA), and lower-order aberration (LOA) were positively or negatively correlated with TSA in the patients with EL (r = 0.681, P &lt; 0.001).Conclusions: Corneal spherical aberration was low in the patients with EL especially for MFS and tended to increase with aging. Preoperatively, individual measurement of CSA was necessary for bilateral EL patients with MFS.

Cross-sectional structural parameters from densitometry

2002 ◽  
Vol 35 (4) ◽  
pp. 511-516 ◽  
Author(s):  
Tammy M Cleek ◽  
Robert T Whalen
Keyword(s):  
Structural Parameters ◽  
Cross Sectional

Biomechanics of Skateboarding: Kinetics of the Ollie

2006 ◽  
Vol 22 (1) ◽  
pp. 33-40 ◽  
Author(s):  
Edward C. Frederick ◽  
Jeremy J. Determan ◽  
Saunders N. Whittlesey ◽  
Joseph Hamill
Keyword(s):  
Initial Phase ◽  
Body Position ◽  
Center Of Mass ◽  
Reaction Force ◽  
Landing Position ◽  
Impact Peak ◽  
Wooden Platform ◽  
Kinetics Of ◽  
Anterior Posterior ◽  
Pronounced Peak

Seven top amateur or professional skateboarders (BW = 713 N ± 83 N) performed Ollie maneuvers onto and off an elevated wooden platform (45.7 cm high). We recorded ground reaction force (GRF) data for three Ollie Up (OU) and Ollie Down (OD) trials per participant. The vertical GRF (VGRF) during the OU has a characteristic propulsive peak (M = 2.22 body weight [BW] ± 0.22) resulting from rapidly rotating the tail of the board into the ground to propel the skater and board up and forward. The anterior-posterior (A-P) GRF also shows a pronounced peak (M = 0.05 ± 0.01 BW) corresponding with this propulsive VGRF peak. The initial phase of landing in the OD shows an impact peak in VGRF rising during the first 30 to 80 ms to a mean of 4.74 ± 0.46 BW. These impact peaks are higher than expected given the relatively short drop of 45.7 cm and crouched body position. But we observed that our participants intentionally affected a firm landing to stabilize the landing position; and the Ollie off the platform raised the center of mass, also contributing to higher forces.

Kinematic Analysis of Dance-Based Exergaming: A Cross-Sectional Study

2021 ◽  
Author(s):  
Ernest K. Ofori ◽  
Savitha Subramaniam ◽  
Shuaijie Wang ◽  
Tanvi Bhatt
Keyword(s):  
Older Adults ◽  
Young Adults ◽  
Postural Stability ◽  
Center Of Mass ◽  
Cross Sectional Study ◽  
Cross Sectional ◽  
Healthy Older Adults ◽  
Age Related ◽  
Aging Populations ◽  
Cortical Pathology

Background: Recent studies demonstrate improvements in both postural stability and mobility among aging populations and those with stroke who are exposed to dance-based exergaming (DBExG). However, age-related deficits and aging with cortical pathology may lead to distinct movement adaptation patterns during DBExG, which could impact therapeutic outcomes.Aim: The aim of this study was to examine the movement kinematics (postural stability and mobility) of healthy older adults, older adults with stroke, and young adults for different paces of dance during DBExG. Method: The study included 33 particpants (11 participant from each group of healthy older adults, older adults with chronic stroke, and healthy young adults) who performed the DBExG using slow- (SP), medium- (MP), and fast-paced (FP) songs with movements in the anteroposterior (AP) and mediolateral (ML) directions. Center of mass (CoM) sway area, excursion (Ex), and peaks as well as hip, knee, and ankle joint excursions were computed. Results: Results of the study revealed that CoM sway areas and Exs were greater for healthy young adults than for older adults with stroke for the SP dance (p < 0.05) and that there were significantly more AP CoM peaks for young adults than for healthy older adults and those with stroke for the FP dance (p < 0.05). Young adults also exhibited greater hip and ankle Exs than older adults with stroke (p < 0.05) for all song paces. Similarly, knee and ankle Exs were greater for healthy older adults than for older adults with stroke for all song paces (p < 0.05). Conclusion: The quantitative evaluation and comparison of the movement patterns presented for the three groups could provide a foundation for both assessing and designing therapeutic DBExG protocols for these populations.

Long bone cross-sectional geometry

2020 ◽  
pp. 307-320
Author(s):  
Christopher B. Ruff ◽  
Ryan W. Higgins ◽  
Kristian J. Carlson
Keyword(s):  
Mechanical Properties ◽  
Cross Sections ◽  
Lateral Displacement ◽  
Center Of Mass ◽  
Gait Pattern ◽  
Locomotor Behavior ◽  
The Body ◽  
Long Bone ◽  
Cross Sectional ◽  
Body Center

Long bone diaphyseal cross-sectional geometries reflect the mechanical properties of the bones, and can be used to aid in inferences of locomotor behavior in extinct hominins. This chapter considers all available long bone diaphyseal and femoral neck cross-sections of specimens from Sterkfontein Member 4, and presents comparisons of these section properties and other cross-sectional dimensions with those of other early hominins as well as modern samples. The cross-sectional geometry of the Sterkfontein Member 4 long bone specimens suggests some similarities to, but also interesting differences in, mechanical loading of these elements relative to modern humans. The less asymmetric cortical bone distribution in the Sterkfontein femoral necks is consistent with other evidence above indicating an altered gait pattern involving lateral displacement of the body center of mass over the stance limb. The relatively very strong upper limb of StW 431 implies that arboreal behavior formed a significant component of its locomotor repertoire. Bipedal gait may have been less efficient and arboreal climbing more prevalent in the Sterkfontein hominins.

scholarly journals Hallux Valgus Surgery May Produce Early Improvements in Balance Control

2013 ◽  
Vol 103 (6) ◽  
pp. 489-497 ◽  
Author(s):  
Saba Sadra ◽  
Adam Fleischer ◽  
Erin Klein ◽  
Gurtej S. Grewal ◽  
Jessica Knight ◽  
...  
Keyword(s):  
Hallux Valgus ◽  
Study Design ◽  
Balance Control ◽  
Center Of Mass ◽  
Cross Sectional Study ◽  
Static Balance ◽  
Long Term Effects ◽  
Cross Sectional ◽  
Eyes Open ◽  
Falls In Older Adults

Background: Hallux valgus (HV) is associated with poorer performance during gait and balance tasks and is an independent risk factor for falls in older adults. We sought to assess whether corrective HV surgery improves gait and balance. Methods: Using a cross-sectional study design, gait and static balance data were obtained from 40 adults: 19 patients with HV only (preoperative group), 10 patients who recently underwent successful HV surgery (postoperative group), and 11 control participants. Assessments were made in the clinic using body-worn sensors. Results: Patients in the preoperative group generally demonstrated poorer static balance control compared with the other two groups. Despite similar age and body mass index, postoperative patients exhibited 29% and 63% less center of mass sway than preoperative patients during double-and single-support balance assessments, respectively (analysis of variance P =.17 and P =.14, respectively [both eyes open condition]). Overall, gait performance was similar among the groups, except for speed during gait initiation, where lower speeds were encountered in the postoperative group compared with the preoperative group (Scheffe P = .049). Conclusions: This study provides supportive evidence regarding the benefits of corrective lower-extremity surgery on certain aspects of balance control. Patients seem to demonstrate early improvements in static balance after corrective HV surgery, whereas gait improvements may require a longer recovery time. Further research using a longitudinal study design and a larger sample size capable of assessing the long-term effects of HV surgical correction on balance and gait is probably warranted. (J Am Podiatr Med Assoc 103(6): 489–497, 2013)

EP-1101 RECTAL AIR REMOVAL REDUCES RECTAL CROSS-SECTIONAL AREA BUT DOESN'T MODIFY CENTER OF MASS OF PELVIC ORGANS

2012 ◽  
Vol 103 ◽  
pp. S425-S426
Author(s):  
S. Sabater ◽  
I. Andres ◽  
V. De la Vara ◽  
M.J. Muñoz ◽  
E. Jimenez ◽  
...  
Keyword(s):  
Center Of Mass ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Pelvic Organs ◽  
Air Removal

A Novel and Reproducible Classification of the Vertebral Artery in the Subaxial Cervical Spine

2019 ◽  
Vol 18 (6) ◽  
pp. 676-683
Author(s):  
Fabian Winter ◽  
Ichiro Okano ◽  
Stephan N Salzmann ◽  
Colleen Rentenberger ◽  
Jennifer Shue ◽  
...  
Keyword(s):  
At Risk ◽  
Cervical Spine ◽  
High Risk ◽  
Vertebral Artery ◽  
Intrarater Reliability ◽  
Cross Sectional ◽  
Cervical Spine Surgery ◽  
Subaxial Cervical Spine ◽  
Anterior Posterior

Abstract BACKGROUND An injury of the vertebral artery (VA) is one of the most catastrophic complications in the setting of cervical spine surgery. Anatomic variations of the VA can increase the risk of iatrogenic lacerations. OBJECTIVE To propose a novel and reproducible classification system that describes the position of the VA based on a 2-dimensional map on computed tomography angiographs (CTA). METHODS This cross-sectional retrospective study reviewed 248 consecutive CTAs of the cervical spine at a single academic institution between 2007 and 2018. The classification consists of a number that characterizes the location of the VA from the medio-lateral (ML) aspect of the vertebral body. In addition, a letter describes the VA location from the anterior-posterior (AP) aspect. The reliability and reproducibility were assessed by 2 independent raters on 200 VAs. RESULTS The inter- and intrarater reliability values showed the classification's reproducibility. The inter-rater reliability weighted κ-value for the ML aspect was 0.93 (95% CI: 0.93-0.93). The unweighted κ-value was 0.93 (95% CI: 0.86-1.00) for “at-risk” positions (ML grade ≥1), and 0.87 (95% CI: 0.75-1.00) for “high-risk” positions (ML grade ≥2). The weighted κ-value for the intrarater reliability was 0.94 (95% CI: 0.95-0.95). The unweighted κ-values for the intrarater reliability were 0.95 (95% CI: 0.91-0.99) for “at-risk” positions, and 0.87 (95% CI: 0.78-0.96) for “high-risk” positions. CONCLUSION The proposed classification is reliable, reproducible, and independent of individual anatomic size variations. The use of this novel grading system could improve the understanding and interdisciplinary communication about VA anomalies.

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