L6: Vision I

Question 1

define refraction

Answer 1

the bending of light waves at an angulated surface of a transparent material

Question 2

light striking a perpendicular surface will ?

Answer 2

continue thru w/o bending

Question 3

what does the degree of refraction depend on ?

Answer 3

1. ratio of two refractive indices of the 2 medias

2. degree of angulation between the interface and entering waves

Question 4

define refractive index

Answer 4

the ratio of the velocity of light in air to the velocity of light traveling in the substance

RI of air = 1.0

Question 5

define refractive power

Answer 5

a measure of how much a lens bends light waves

measured in diopters

Question 6

define diopter

Answer 6

1 diopter = 1 meter / focal length of lens

Question 7

define focal point

Answer 7

the point thru which all parallel rays of light will pass

after passing thru the lens

Question 8

define focal length

Answer 8

the distance from lens center to focal point

Question 9

function of iris

Answer 9

controls the amount of light entering the eye

from darkness to light conditions

Question 10

total refractive power of the eye

Answer 10

59 diopters

Question 11

refractive indices of parts of the eye: cornea, aqueous humor, lens, vitreous humor

Answer 11

cornea = 1.38
ah = 1.33
lens = 1.4
vh = 1.34

Question 12

define emmetropia

Answer 12

a person with ideal/perfect vision

parallel light rays from distant objects come into sharp focus on the retina when ciliary muscles completely relax

all distant objects can be seen clearly

Question 13

define hyperopia

Answer 13

farsightedness

being able to seen far objects clearly but closer objects are not clear

Question 14

cause of hyperopia

Answer 14

usually due to an eyeball that is too short
or
occasionally a lens system that is too weak

Question 15

define myopia

Answer 15

nearsightedness
cannot see distant objects but closer things are clear

when ciliary muscle is completely relaxed, light rays coming from distant objects are focused in from of the retina

Question 16

cause of myopia

Answer 16

usually due to too long of an eyeball

compared to the focusing power of the eye

Question 17

define visual acuity

Answer 17

a measure of the resolving power of the eye

Question 18

average diameter of a cone
and
max visual acuity for 2-pt sources of light

Answer 18

average d for cone = 1.5 micrometer
thus
max va for 2-pt source is = 1.5 to 2 micrometers

Question 19

depth of focus of the lens ______ as the pupillary diameter ______.

Answer 19

increases
decreases

negative relationship

Question 20

ions moved to create aqueous humor

Answer 20

ions drawn into space in ciliary apparatus created by 2 layers of epithelial cells

Na active trans in
Cl in
bicarbonate in

Question 21

how is aqueous humor

Answer 21

as the ions are drawn into the space
water follows via osmosis

thus creating an aqueous solution that is passed into the anterior chamber

Question 22

flow of fluid in the eye

Answer 22

fluid flows from:
ant. chamber
canal of schlemm
aqueous veins in sclera

Question 23

what is used to measure intraocular pressure?

Answer 23

tonometer

normal p = 15 mmHg

Question 24

how is a tonometer used?

Answer 24

eye is numbed and a stain applied

a tool is used to just touch the cornea and can measure the pressure w/in the eye

cheaper way but less accurate is the air pistol where they put a puff of air into the eye

Question 25

what is glaucoma? | why is it so dangerous?

Answer 25

increased fluid pressure in your eye this increased p can damage the optic nerve and lead to blindness the fluid drains too slow, so pressure slowly builds but it is painless so it can happen over years w/o notice

Question 26

photosensitive pigments in rods and cones

Answer 26

rods = rhodopsin cones = 3 dif. color pigments

Question 27

list the functional parts of photoreceptors

Answer 27

outer segment inner segment nucleus synaptic body

Question 28

outer segment

Answer 28

site of light sensitive photochemicals

Question 29

inner segment

Answer 29

contains organelles | especially mito

Question 30

synaptic body

Answer 30

connects w/ horizontal and bipolar cells

Question 31

how does light affect rhodopsin?

Answer 31

rhodopsin + light = converts 11cis-retinal to all trans-retinal requires isomerase and metabolic nrg to return to normal

Question 32

metarhodopsin II

Answer 32

an intermediate between the transforming of retinal it excites electrical changes in rods

Question 33

vitamin A is also called?

Answer 33

all-trans-retinol an alternate pathway for all-trans-retinal to return to 11-cis-retinal

Question 34

results of an excited rod

Answer 34

--increased negativity of intrarod memb. potential (hyperpolarization)

Question 35

decomposition of rhodopsin ?

Answer 35

decreases rod memb. conductance for Na ions in the outer segment resulting in hyperpolarization of entire rod memb.

Question 36

describe outer segment membrane of rods in dark

Answer 36

leaky to Na ions that flow thru cGMP-gated channels this slow leak into cell neutralizes the negativity of the entire cell thus reduced electronegativity in dark conditions -40mV instead of normal -70 to -80 mV

Question 37

inner segment of rods

Answer 37

continuously pumps Na out and K in K leaks out via non-gated channels a negative potential is created inside cell

Question 38

when rhodopsin is exposed to light?

Answer 38

it begins to decompose the retinal portion is activated and stims transducin (G-protein)

Question 39

active transducin

Answer 39

activates cGMP phosphodiesterase which catalyzes cGMP to 5'GMP

Question 40

reduction in cGMP causes?

Answer 40

closure of Na channels thus rod becomes hyperpolarized

Question 41

when rhodopsin is activated, __________ channels close for each ?

Answer 41

several hundred channels close for each rhodopsin molecule activated

Question 42

cones are similar to rods except that the protein portions (_____) of the photochemicals are ?

Answer 42

opsins | are dif. from the scotopsin in the rod photochemicals

Question 43

colors cones are sensitive to?

Answer 43

blue green red overlapping of light absorption spectrum results in humans ability to see wide number of colors

Question 44

wavelength of colors

Answer 44

blue = 390 - 530 green = 440 - 620 red = 480 - 690

Question 45

scotopsin + 11-cis-retinal = ?

Answer 45

rhodopsin

Question 46

rhodopsin + light = ?

Answer 46

scotopsin + all-trans-retinal now that it is converted it will separate from scotopsin

Question 47

alternative pathway using Vit. A

Answer 47

all-trans retinal --> all-trans-retinol all-trans-retinol --> 11-cis retinol ---> 11-cis retinal