Vision: Refraction and Accommodation

Question 1

what is refraction?

Answer 1

light rays bend to form a sharp image in the retina

Question 2

what is accommodation?

Answer 2

the way we focus on far or near objects by changing how much we bend light rays

Question 3

what change occurs in the lens as an object comes closer to the eye?

Answer 3

it becomes thicker and more powerful so a clear image is formed on the retina.

Question 4

what three things happen simultaneously to create accommodation?

Answer 4

> lens changes shape
pupil constricts
eyes converge

Question 5

describe the process by which the lens thickens?

Answer 5

the ciliary muscle contracts (parasympathetic) making the ciliary body bulge and decreasing the space in the middle. the suspensory ligaments become lax so the lens is no longer under stretch and becomes thicker.

Question 6

how does the pupils sharpen focus?

Answer 6

it constricts only allowing a few rays to pass through

Question 7

what innervation does the sphincter pupillae get?

Answer 7

parasympathetic innervation

Question 8

what is convergence?

Answer 8

when focussing on an object close up our eyes have to turn in

Question 9

which muscle is used in convergence?

Answer 9

medial rectus, of both sides

Question 10

which nerve innervate convergence?

Answer 10

CN111 Ocolumotor

Question 11

what is short sightedness called?

Answer 11

myopia

Question 12

what is hyperopia?

Answer 12

long-sightedness

Question 13

what is an astigmatism?

Answer 13

non-spherical curvature of cornea (or lens)

Question 14

what is presbyopia?

Answer 14

long-sightedness of old age

Question 15

what emmetrope?

Answer 15

someone with perfect vision

Question 16

what is the most common cause for myopia?

Answer 16

the eyeball is too long

Question 17

in myopia where does the image form and what is the effect of this?

Answer 17

in front of the retina so images far away are not seen so clearly

Question 18

how is myopia corrected?

Answer 18

decreasing the bending power of the eye with biconcave lenses.

Question 19

what can cause hyperopia?

Answer 19

the eyeball being too short or the cornea and lens being to flat

Question 20

where is the image of distant objects therefore formed?

Answer 20

behind the retina

Question 21

why can people with hyperopia not see things close up?

Answer 21

> the person automatically uses his accommodative power to make the lens thicker and form the image on the cornea
since he is using his lens power to see far off things when trying to visual close up things all his power is used up and he cannot focus on them

Question 22

how is hyperopia corrected?

Answer 22

biconvex lenses focuses distant objects and rests the accommodative power

Question 23

what are the symptoms of hyperopia?

Answer 23

> eyestrain in working on a computer

> convergent squint in children

Question 24

what is the cause of astigmatism?

Answer 24

the surface of the eyeball has different curvatures in different meridians so the bending of light rays along one axis will never be the same as that on another axis.

Question 25

what is the effect of astigmatism on eyesight?

Answer 25

the object always appears hazy at any distance

Question 26

how is astigmatism corrected?

Answer 26

> laser eye surgery
cylindrical glasses, with only one curved axis
toric contact lenses

Question 27

what causes presbyopia?

Answer 27

the lens becomes less mobile and elastic with age so it is not capable to change shape when the ciliary muscle contracts

Question 28

how would you correct presbyopia?

Answer 28

biconvex reading glasses