Unit 3 Notes:

Vision

(1) Types of Eyesight

• Emmetropia = Perfect Eyesight�
• Myopia = Nearsighted�
• Hyperopia = Farsighted�
• Astigmatism = Nearsighted + Farsighted

(2) Myopia (Nearsighted)

• Cause:
• Cornea is too curved or bulging.
• Light is over focused and refracted before hitting the retina.
• Light rays scatter before hitting the retina.
• Scattered light = blurred vision.�
• Solution:
• Put a thin lens in front of the cornea.
• The thin lens will spread out the light rays more.
• Decreases refraction so light rays are concentrated when hitting retina.

(3) Hyperopia (Farsighted)

• Cause:
• Cornea is too flat.
• Light is under focused and refracted before hitting the retina.
• Light rays scatter before hitting the retina.
• Scattered light = blurred vision.�
• Solution:
• Put a thick lens in front of the cornea.
• The thick lens will concentrate the light rays more.
• Increases refraction so light rays are concentrated when hitting retina.

(4) Astigmatism (Near + Farsighted)

• Cause:
• Cornea is flattened in one area, and bulging in another area.
• Light is under and over focused in the different areas, before hitting the retina.
• Light rays scatter before hitting the retina.
• Scattered light = blurred vision.�
• Solution:
• Put a lens which has a thick region, and a thin region, in front of the cornea.
• The thick area will concentrate the light rays more, the thin area will spread out the light rays as needed.