Accommodation Flashcards
What is accomodation?
It is a reflex mechanism.
Light rays from an object are brought to focus and land on the retina at the fovea.
This region contains a high density of cones and so is able to detect images in detail.
What is the cornea responsible for?
For most of the refraction (bending) of light to focus the image.
What is the lens responsible for?
Fine focusing is carried out by the lens which can change shape according to how far away the object is.
The image produced is;
- Upside down,
- reversed, and
- usually diminished in size.
When the impulses are recieved by brain, the optic centre interprets the information so that the image is percieved correctly.
Light from a distant object:
Light rays are ____
Almost parallel
Light from a distant object entering the eye does not need bent much.
Light from a distant object:
Ciliary muscles ____
Relax
Larger ring of muscle which transfers the tension in the wall of the eyeball through the ligaments to the lens.
Light from a distant object:
Tension in the eyeball is ____
Tranferred to lens by ligaments
Light from a distant object:
Suspensory ligaments are ____
Pulled taut
Light from a distant object:
The shape of the lens is ____
Less convex (thinner)
Light from a distant object:
Refraction of light is ____
Decreased
Light rays focused onto retina at the fovea.
Light from a near object:
Light rays are ____
Diverging
Light from a near object as it enters the eye needs bent a lot.
Light from a near object:
Ciliary muscles ____
Contract
Smaller ring of muscle which reduces tension on the ligaments.
Light from a near object:
Tension in the eyeball is ____
Not transferred
Light from a near object:
Suspensory ligaments have ____
No tension
Ligaments are slack so they don’t pull on the lens.
Light from a near object:
The shape of the lens is ____
More convex (thicker)
Due to elasticity of the lens it returns to a fat shape.
