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Questions and Answers

What is myopia commonly known as?

  • Far-sightedness
  • Presbyopia
  • Near-sightedness (correct)
  • Astigmatism

Which type of lens is used to correct myopia?

  • Concave lens (correct)
  • Convex lens
  • Cylindrical lens
  • Bifocal lens

What occurs in the eye of a person with hypermetropia?

  • The lens is too curved
  • The near point is farther away than 25 cm (correct)
  • Images are formed in front of the retina
  • The far point is closer than infinity

How is hypermetropia corrected?

<p>By using a convex lens (A)</p> Signup and view all the answers

What causes myopia in the eye?

<p>Excessive curvature of the lens or elongation of the eyeball (A)</p> Signup and view all the answers

What is Presbyopia primarily caused by?

<p>Weakening of the ciliary muscles and lens flexibility (A)</p> Signup and view all the answers

What type of lenses do people who suffer from both myopia and hypermetropia typically require?

<p>Bi-focal lenses (A)</p> Signup and view all the answers

What is the function of the upper portion of a bi-focal lens?

<p>To correct distance vision (B)</p> Signup and view all the answers

Which statement is true regarding the power of accommodation in the eye?

<p>It decreases with age (C)</p> Signup and view all the answers

How can refractive defects in the eyes be corrected?

<p>By corrective eye-glasses or surgical interventions (C)</p> Signup and view all the answers

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Study Notes

Common Visual Defects and Their Corrections

  • Myopia (Near-sightedness): A condition where distant objects are blurred, while nearby objects are clear, due to the far point being closer than infinity.
  • Hypermetropia (Far-sightedness): A condition where distant objects are clear, but nearby objects are blurred, resulting in a near point further away than the typical 25 cm.
  • Presbyopia: An age-related condition where the eye's accommodation ability decreases, making it difficult to focus on near objects.

Myopia

  • Caused by excessive curvature of the eye lens or elongation of the eyeball.
  • Distant images are focused in front of the retina.
  • Corrected using concave lenses that redirect light to focus it on the retina.

Hypermetropia

  • Caused by a long focal length of the eye lens or a smaller eyeball size.
  • Nearby images are focused behind the retina, requiring objects to be placed beyond 25 cm for clear vision.
  • Corrected using convex lenses to converge light rays onto the retina.

Presbyopia

  • Occurs due to the weakening of ciliary muscles and reduced flexibility of the eye lens with age.
  • Near point gradually increases, affecting the ability to see close objects clearly.
  • Often requires bifocal lenses that combine concave (for distance) and convex (for near) corrections.

Correction Methods

  • Eyeglasses: Utilize spherical lenses (concave for myopia, convex for hypermetropia) for vision correction.
  • Contact lenses: Provide alternative vision correction directly on the eye's surface.
  • Surgical interventions: Offer permanent solutions for refractive defects.

Anatomy of the Eye

  • Power of accommodation: The eye's ability to adjust focal length for focusing on objects at varying distances.
  • Near point: Closest distance for clear vision, approximately 25 cm for young adults.
  • Far point: Distant limit, ideally infinity for normal vision.

Refraction of Light

  • Light rays change direction as they pass through different mediums (like air to glass), resulting in refraction.
  • Triangular prisms bend light, leading to an angle of deviation when light exits.

Scattering of Light

  • Tyndall effect: Scattering of light by particles in a medium, visible in smoke or mist.
  • The blue sky is a result of shorter wavelength light (blue) scattering more effectively than longer wavelengths like red.
  • Red light's ineffectiveness at scattering allows it to be prominent during foggy conditions.

Additional Important Facts

  • Stars twinkle due to atmospheric disturbances affecting light paths, while planets do not twinkle because they have a more stable view.
  • In high altitudes, light scattering is minimal, resulting in a darker sky.
  • Eye donations after death can provide vision for the blind, reflecting the importance of eye health.

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