eye refraction and accomodation Flashcards
What is refraction
Bending of light when it passes from one optical medium to another
What is meant by the lens being able to change its refractive index
The lens is connected to the cilliary body by zonules which can change the shape of the lens and therefore change the refractive index
At what range do divergent eyes reach the eye
Less than 6m away - only parallel rays reach the eye further than 6m away
How does the eye deal with divergent rays
The lens has to become thicker to bend the image more to bring them onto focus into the retina
What is accomodation of the eye
Changes in the eye as it changes from a distant to clos object
Describe how the lens becomes thicker
the ciliary body contracts which causes the lens to become thicker and more spherical
Describe how accomodation occurs
- The lens thickens
- The pupils constricts
- The eyes converge
What muscles are used to converge the eyes during accomodation
The medial rectus muscles
What is myopia
Short signtedness
What is hyperopia
Long sightedness
What is astigmatism
nON-SPHERICAL CURVATURE OF THE CORNEA OR THE LENS
What is presbyopia
Long sightedness of old age
What is an emmetrope
Perfect vision
What is short sightedness
Closer objects look clear while distant objects are blurry
Describe how myopia occurs
The bending power of the cornea and the lens is too much so when they bend the rays of light, they make the image infront of the retina
What is the treatment of myopia
Biconcave lens to decrease the bending power - have a negative power
Describe how hyperopia occurs
The person uses their accomodative power too early so by the time the objects are close so their is no power left for accomodation and the image is formed behind the retina
