eye reflexes

Question 1

what are the refractive media in order and their refractive power?

Answer 1

cornea=40 diopeters
aqueous humour
lens=20 diopeters
Vitreous humour

Question 2

what is the total refractive power of the eye?

Answer 2

59 diopeters

Question 3

describe the cornea

Answer 3

its hard enough to protect the eye ball and absorbs ultraviolet rays and have corneal reflex

Question 4

what is the corneal reflex?

Answer 4

its a very sensitive reflex to touch
afferent is the ophthalmic division of trigeminal nerve sending signals to the facial motor nucleus which sends to the efferent nerve the facial nerve which stimulates the effector the orbicularis oculi muscle stimulating eyelids to close

Question 5

describe the lens

Answer 5

transparent avascular biconvex structure that has a refractive power of 20 diopters and its suspended by suspensory ligaments

Question 6

what is the accommodation of lens?

Answer 6

changing its curvature and its refractive power to be able to see near objects

Question 7

how does an individual see a light ray at a distance less than 6 meters

Answer 7

light rays are diverging and image is focused behind the retina therefore accommodation occurs to increase curvature and refractive power of the lens to be able to focus image on the retina

Question 8

role of cillary muscle in accommodation?

Answer 8

cillary muscle contracts loosening the suspensory ligament allowing lens to become more curved

Question 9

describe the pathway of the cillary muscle contraction?

Answer 9

parasympathetic preganglionic nerve fibers arise from the edinger nucleus and relay in the cillary ganglion and reach the eye ball. occulomotor nerve affects 2 muscles:
1)cillary muscles
2)constrictor pupilli muscles

Question 10

what are the associated movements for accommodation of a near object

Answer 10

1)contraction of the circular muscles of the iris to narrow the pupil
2) converging my the medial rectus muscles

Question 11

describe the nervous pathway for accommodation reflex

Answer 11

the center of this pathway is the superior colliculus in the midbrain it then sends nerve fibres to the edinger nucleus and it then sends signals to cillary ganglion and finally the eyeball. another pathway is where the superior colliculus sends to the somatic nucleus/oculomotor nucleus which sends signals to the medial rectus muscles for converging

Question 12

what is presbyopia?

Answer 12

loss of ability of accommodation. with aging the lens gets bigger thicker and less elastic mostly due to denaturing of the proteins of the eye. accommodation changes from 14 diopters in kids to only 2 diopters by the age of 45

Question 13

what is myopia?

Answer 13

the image falls in front of the eye because person have large eye ball requires concave lens this person accommodates at a closer distance than 6m

Question 14

what is hyperopia?

Answer 14

the image falls behind the retina because person have a small eyeball and requires convex lens. this person accommodates for far objects

Question 15

pupillary reflexes?

Answer 15

1)control amount of light entering the eye
2) pupillary diameter is controlled by autonomic nerves
3)pupillary diameter can change from 1.5mm to 8mm

Question 16

what is a direct pupillary reflex?

Answer 16

its the constriction of the pupil in the eye which is directly stimulated by light

Question 17

what is an indirect pupillary reflex?

Answer 17

its the constriction of the pupil in the eye that is not directly stimulated by light

Question 18

describe the pupillary light reflex pathway

Answer 18

1)receptors: rods and cones
2)afferent: optic nerve optic chiasma and optic tract
3)centre is the pretectal nucleus of the midbrain
4)efferent:edinger nucleus and oculomotor nucleus
5)effector: sphincter pupillae
6) response constriction of pupil

Question 19

what happens during the consensual light reflex?

Answer 19

1) crossing of the nasal fibres in optic chiasma stimulates both pupils to constrict
2)bilateral innervation of the edinger nucleus from each pretectal nucleus

Question 19

what happens during the consensual light reflex?

Answer 19

1) crossing of the nasal fibres in optic chiasma stimulates both pupils to constrict
2)bilateral innervation of the edinger nucleus from each pretectal nucleus

Question 20

what happens during the consensual light reflex?

Answer 20

1) crossing of the nasal fibres in optic chiasma stimulates both pupils to constrict
2)bilateral innervation of the edinger nucleus from each pretectal nucleus

Question 20

what happens during the consensual light reflex?

Answer 20

1) crossing of the nasal fibres in optic chiasma stimulates both pupils to constrict
2)bilateral innervation of the edinger nucleus from each pretectal nucleus

Question 21

what is the argyll Robertson pupil

Answer 21

damage in the pretectal nucleus which is the center of the light reflex pathway so it will be lost while the accommodation reflex is not affected because its center is the superior colliculus