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Curve Equations01:17

Curve Equations

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Curves are essential geometric elements characterized by tangent distance, chord length, middle ordinate, and total arc length. These measurements are crucial in understanding a curve's geometric and spatial properties and are defined by the relationship between its radius and its central angle.The tangent distance (T) refers to the straight-line measurement from the intersection point of two tangents to either the start or end of the curve. This distance is influenced by the curve's radius (R)...
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Mohr's Circle for Plane Strain01:18

Mohr's Circle for Plane Strain

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Mohr's circle is a crucial graphical method used to analyze plane strain by plotting strain on a set of cartesian coordinates, where the abscissa is normal strain ∈ and the ordinate is shear strain γ. Similarly to Mohr’s circle for plane stress, two points X and Y are plotted. Their coordinates are (∈x, -γXY) and (∈Y, γXY), respectively.
Mohr's circle visually represents the strain states under various conditions, which is essential for...
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Three-Dimensional Analysis of Strain01:29

Three-Dimensional Analysis of Strain

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Three-dimensional strain analysis is crucial for understanding how materials deform under stress, particularly in elastic, homogeneous materials. This method employs principal stress axes to simplify complex stress states into more understandable forms. Subjected to stress, a small cubic element within a material either expands or contracts along these axes, transforming into a rectangular parallelepiped. This transformation effectively illustrates the material's deformation. The principal...
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Measurements of Strain01:27

Measurements of Strain

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Strain quantifies the deformation of a material under force, typically measured as normal strain, which represents the change in length when compared with the original length. Electrical strain gauges are used for enhanced accuracy. These devices consist of a conductive wire mounted on a paper backing that adheres to the material's surface. These gauges operate on the piezoresistive effect, where the wire's electrical resistance changes in response to mechanical deformation. The strain...
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Related Experiment Video

Updated: Aug 4, 2025

Software-Assisted Quantitative Measurement of Osteoarthritic Subchondral Bone Thickness
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Measurement of the visual axis through two different methods: quantification and differences for measuring chord μ.

Pablo Felipe Rodrigues1,2, Bernardo Kaplan Moscovici1, Luciano Lamazales2

  • 1Department of Ophthalmology and Visual Sciences, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP, Brazil.

Arquivos Brasileiros De Oftalmologia
|March 30, 2023
PubMed
Summary

This study compared apparent and actual chord μ measurements using Pentacam and HD Analyzer, finding a moderate correlation but significant differences. Both devices are useful in practice, but their unique characteristics must be considered.

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Area of Science:

  • Ophthalmology
  • Optometry
  • Corneal Imaging

Background:

  • Accurate corneal measurements are crucial for refractive surgery and contact lens fitting.
  • Understanding discrepancies between different measurement devices is essential for clinical decision-making.

Purpose of the Study:

  • To compare apparent and actual chord μ measurements obtained from Pentacam and HD Analyzer.
  • To evaluate the correlation and differences between these two devices in measuring corneal parameters.

Main Methods:

  • A prospective, comparative study involving 116 eyes of 58 patients (aged 21-71) with myopia and mild astigmatism.
  • Corneal imaging was performed using Pentacam and HD Analyzer under scotopic conditions.
  • Exclusion criteria included contact lens wear, prior eye surgery, and corneal abnormalities.

Main Results:

  • A moderate positive linear relationship (Pearson's r=0.647) was observed between apparent and actual chord μ.
  • Mean differences of 52.45 μm were found between the devices (p=0.01).
  • Mean pupillary diameters measured were 5.76 mm (HD Analyzer) and 3.31 mm (Pentacam).

Conclusions:

  • A correlation exists between Pentacam and HD Analyzer for chord μ measurements.
  • Significant differences were noted, indicating that both devices can be utilized in clinical practice.
  • Clinicians should acknowledge and respect the unique characteristics of each measurement device.