Defects of Vision

• What is another name for short-sightedness?

  Myopia

  
• What causes short-sightedness?

  When the lens is more curved than normal
• How does myopia affect light rays?

  Light rays are refracted too much
• Where does the focal point of the image fall in myopia?

  In front of the retina
• What visual issue do people with short-sightedness experience?

  Distant objects appear blurry
• What is the treatment for short-sightedness?

  • Contact lenses
  • Glasses with diverging (concave) lens
• How do diverging lenses help short-sighted individuals?

  They cause light rays to diverge before reaching the eye

  
• What is the focal length of a diverging lens?

  Negative focal length
• Why can short-sighted people remove glasses for close-up tasks?

  They can easily focus on close objects
• What is the far point of a normal-sighted person?

  At infinity
• How does the far point of a short-sighted person differ?

  It is less than infinity
• What must the diverging lens's principal focus match?

  The eye's faulty far point
• If a short-sighted person has a far point of 8 m, what is the focal length?

  $-8 \text{ m}$
• What is the formula for power of a lens?

  $P =$$\frac{1}{f}$
• What is the power of a lens needed for a far point of 8 m?

  $-0.125 \text{ D}$
• What is another name for long-sightedness?

  Hyperopia

  
• What causes long-sightedness?

  When the lens is less curved than normal
• Where does the focal point of the image fall in hyperopia?

  Behind the retina

  
• What visual issue do people with long-sightedness experience?

  Close objects appear blurry
• What is the treatment for long-sightedness?

  • Contact lenses
  • Glasses with converging (convex) lens
• How do converging lenses help long-sighted individuals?

  They cause light rays to converge before reaching the eye
• Why might a long-sighted person remove glasses when driving?

  They can easily focus on distant objects
• What is the near point of a normal-sighted person?

  About 25 cm
• How does the near point of a long-sighted person differ?

  It is further than 25 cm
• What must the converging lens produce for a long-sighted person?

  A virtual image at the uncorrected near point
• If a long-sighted person has a near point of 6 m, what is the image distance?

  $-6 \text{ m}$
• What is the object distance for a long-sighted person?

  $0.25 \text{ m}$
• What is the lens equation?

  $\frac{1}{f} =$$\frac{1}{u} +$$\frac{1}{v}$
• What is the power of the lens needed for a near point of 6 m?

  $3.8 \text{ D}$
• What is the main cause of astigmatism?

  Irregularly shaped corneas
• How do astigmatic eyes differ from non-astigmatic eyes?

  They have different focal lengths for different planes

  
• What happens when vertical lines are in focus for astigmatic eyes?

  Horizontal lines might not be in focus

  
• How do light rays behave in a spherically shaped cornea?

  They come to the same point of focus
• How do light rays behave in an astigmatic eye?

  They come together at different points of focus

  
• What are the key characteristics of astigmatism?

  • Irregularly shaped corneas
  • Different focal lengths for different planes
  • Difficulty focusing horizontal and vertical lines

  
• What is the effect of astigmatism on vision?

  Struggles to focus horizontal and vertical lines
• What is the impact of the space between the eye lens and correcting lens?

  It affects the overall power slightly
• What is the shape of a normal cornea?

  A perfect sphere
• How does the curvature of the cornea affect vision?

  It determines the focal lengths for different planes
• How does astigmatism affect the perception of structures?

  Structures appear distorted or blurred