Iris Reflex + Accommodation

Question 1

what happens to the iris in dim light?

Answer 1

the radius muscles contract and the circular muscles relax - this makes the iris narrower and the pupil dilates

Question 2

what happens to the iris in bright light?

Answer 2

the circular muscles contract and the radial muscles relax - this makes the iris wider and the pupil constricts

Question 3

what is the reflex arc of the eye when in bright/dim light?

Answer 3

the light intensity is detected by the retina and the effectors are the muscles of the iris

Question 4

what is accommodation?

Answer 4

the changes that take place in the eye which allow us to see objects at different distances

Question 5

what happens eye when it is focusing on an object far away?

Answer 5

light rays entering the eye are almost parallel when they reach the cornea so the lens does not need to refract them much to focus light onto the retina - the eye does this by:

• relaxing ciliary muscles
• meaning suspensory muscles ligaments are therefore pulled tight
• lens is pulled thin and has a less convex shape
• therefore there is less refraction of light

Question 6

what happens when the eye is focusing on an object close up?

Answer 6

light rays entering eye are spreading out (diverging) so the lens needs to refract the light to ensure it focusses onto the retina - the eye does this by:

• contracting the ciliary muscles
• meaning suspensory ligaments are therefore slack
• lens is not stretched out so becomes thicker with more is more convex shape
• therefore there is more
  refraction