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Related Concept Videos

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We have discussed why we form relationships, what attracts us to others, and different types of love. But what determines whether we are satisfied with and stay in a relationship? One theory that provides an explanation is social exchange theory. According to social exchange theory, we act as naïve economists in keeping a tally of the ratio of costs and benefits of forming and maintaining a relationship with others (Rusbult & Van Lange, 2003).
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The cardiovascular system's chief role is to disseminate gases, nutrients, waste, and other substances to the body's cells. Small molecules like gases, lipids, and lipid-soluble substances directly diffuse through capillary wall endothelial cell membranes. Glucose, amino acids, and ions, including sodium, potassium, calcium, and chloride, use transporters for facilitated diffusion via membrane-specific channels. Glucose, ions, and bigger molecules may also pass through intercellular...
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Ion exchange chromatography separates charged molecules from a solution by reversibly exchanging them with mobile, or 'active', ions associated with the oppositely charged stationary phase. This method can be used to separate ions, soften and deionize water, and purify solutions. The polymers comprising the ion-exchange column are high-molecular-weight and chemically stable polymers, crosslinked to be porous and essentially insoluble. They are also functionalized with either acidic or...
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Subjective Refraction Test Using a Smartphone for Vision Screening
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Eye Refraction in Doubly Exchanged Monozygotic Twins.

Nancy L Segal1, Yesika S Montoya2, Fernando Y Peña3

  • 1Department of Psychology,California State University,Fullerton, CA,USA.

Twin Research and Human Genetics : the Official Journal of the International Society for Twin Studies
|June 20, 2019
PubMed
Summary

Spending more time outdoors promotes normal vision and refractive status. This study found rural-raised twins had better uncorrected vision than urban-raised twins, suggesting outdoor time is key for eye health.

Keywords:
Myopiaprevention and controltwin study

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Area of Science:

  • Ophthalmology
  • Genetics
  • Environmental Health

Background:

  • Myopia (nearsightedness) is a growing public health concern globally.
  • Genetic and environmental factors are known contributors to refractive status.
  • Previous studies suggest a link between outdoor time and reduced myopia risk.

Purpose of the Study:

  • To investigate the hypothesis that increased outdoor time leads to normal vision and refractive status.
  • To utilize a unique genetically informative kinship design to examine environmental influences on vision.
  • To compare the visual and refractive status of genetically related and unrelated individuals raised in different environments.

Main Methods:

  • Case study involving two pairs of 29-year-old monozygotic male twins from Bogotá, Colombia.
  • Comprehensive ophthalmological examinations including visual acuity, refraction, and keratometry.
  • Visual life history interviews conducted by ophthalmologists blinded to participant relatedness and rearing status.

Main Results:

  • Rural-raised, unrelated brothers exhibited normal uncorrected vision and refractive status compared to their urban-raised counterparts.
  • Uncorrected visual acuity was significantly better in country-raised twins (20/20 and 20/30) versus city-raised twins (20/160 and 20/200).
  • Factors like premature birth, low birth weight, computer use, and reading time did not account for the observed visual differences.

Conclusions:

  • Time spent outdoors appears to be a significant factor in the development of myopia.
  • This study reinforces existing findings on the protective effect of outdoor time on vision.
  • The novel experimental approach using genetically informative kinships provides strong support for environmental influences on refractive status.