Nervous System

Question 1

What are the 4 ways in which the eye function

Answer 1

• Refraction of light rays by the cornea and the lens
• Accommodation
• Pupillary Mechanism
• Binocular Vision

Question 2

Explain each way in which the eye functions fully

Answer 2

1) Light rays enter eye through cornea; AH; pupil; lens;VH and fall on retina

2) Near vision = CM contract pulling C- process and choroid towards lens. Elastic lens becomes more convex incr refractive power and a clear image is formed on retina

Distant vision = CM relax and C-process and choroid return to normal position. tension in SL is incr and lens becomes less convex, clear image formed

3) Bright light = circular muscles of iris contract and radial muscles relax causing pupil size to decrease allowing less light into eye

Dim light = circular muscles of iris relax and radial muscles contract causing pupil size to incr allowing more light into eye

Question 3

Explain visual defects fully

Answer 3

• Short sightedness = focus clearly on close objects because eyeball is too long and light rays from distant obj sharply come into focus on retina ( concave lens )
• Long sightedness = can see distant obj clearly because their eyeball is too short which results in the close obj coming sharply into focus behind retina ( convex lens )
• Astigmatism = cornea / lens having unequal curvature, causing only part of the image to be sharply in focus
• Cataracts = lens becomes cloudy and vision is impaired