Physiology of Vision

Question 1

what is a blind spot (optic disc)?

Answer 1

no retinal space bc optic artery and central retinal artery run here, this equals no photoreceptors

Question 2

what is significant about the corneal epithelium?

Answer 2

replenished every 24 hours so minor abrasions are not a big deal

Question 3

what is the cornea?

Answer 3

thin transporting epithelium devoid of blood vessels, cell structure maintains high transparency; backed by anterior chamber + aqueous humor

Question 4

what are the lens?

Answer 4

closely packed columnar cells arranged in concentric shells and sheathed by thin, tough, transparent capsule composed of epithelial cells, not that the vitreous humor is behind this and is more viscous than the aqueous humor

Question 5

what is the superior tarsus?

Answer 5

smooth muscle inside the tarsal plate along with levator palpebrae superioris to move eyelid

Question 6

whats is the innervation of the superior tarsus?

Answer 6

sympathetic innervation, ptosis can develop and so if innervation is lost than horner syndrome can develop

Question 7

this secretes fluid to facilitate the movement of the eyeball in orbit? how can this be blocked

Answer 7

tarsal (meibomian glands); this can be blocked by eyeliner buildup or contact lens not cleaned

Question 8

what is the lacrimal apparatus? who is most affected

Answer 8

bathes eye to remove airborne debris from the surface and protect eye from infection

babies often have bulging lacrimal sac that can resolve or surgery can fix it

Question 9

what bounds the aqueous compartment?

Answer 9

bounded by cornea and suspensory ligaments

Question 10

what chambers are found in the aqueous compartment?

Answer 10

anterior chamber(behind cornea to anterior surface of the iris) and the posterior chamber (behind the iris to suspensory ligaments)

both filled with aqueous humor

Question 11

what is the vitreous compartment

Answer 11

from the suspensory ligaments that contain the vitreous body

Question 12

in terms of circulation of fluid in the eye, this circulates freely in the anterior compartment?

Answer 12

intraocular fluid

Question 13

what type of fluid in found in the posterior compartment?

Answer 13

vitreous humor

the posterior compartment has a fine fibrillar meshwork of macropolyglycans through which this intraocular fluid slowly diffuses

Question 14

the intraocular fluid is drained by what canal?

Answer 14

canals of Schlemm which are veins surrounded by trabeculae which filter fluid as it drains

Question 15

what is the angle between the cornea and the iris?

Answer 15

iridocorneal angle (ICA)

Question 16

what is the leading cause of blindness?

Answer 16

open angle glaucoma

Question 17

what are the two major components of the eye?

Answer 17

optical part (gathers, focuses light to form image)

neural part (retina) which converts optical image into neural code

Question 18

so we know that electromagnetic spectrum goes all the way from gamma rays to AC circuits but we see things around?

Answer 18

10^-6 wavelength

Question 19

how does the ray of light enter the eye?

Answer 19

passes through transparent elements to reach retina: thin film tears -> cornea -> aqueous humor -> lens -> vitreous humor -> retina

Question 20

what are tears made of?

Answer 20

plasma ultrafiltrate which bathes the cornea

Question 21

why does most focusing take at interface between air and tear covered anterior surface of the cornea?

Answer 21

because its the biggest change in refractive index

Question 22

what is accommodation?

Answer 22

increasing focal power to focus on objects by changing the shape of the lens

Question 23

to shift focal point closer how does the lens accomodate?

Answer 23

ciliary muscle fibers contract and suspensory ligaments relax = lens become rounder

Question 24

this is a medical condition that happens with age and so the lens become stiffer and less able to round and accomodate

Answer 24

presbyopia

Question 25

this medical condition results from uneven curvature of refractive surfaces of the eye and so the point of light can’t be brought to precise focus on the retina and so diffuse focusing causes blurring of image

Answer 25

astigmatism

Question 26

what are the photoreceptor cells in the retina?

Answer 26

rods and cones

Question 27

what are the rods?

Answer 27

monochromatic dark adapted vision (one type)

Question 28

what are the cones?

Answer 28

3 subtypes responsible for color sensitive vision

Question 29

these light absorbing molecules are found within the retina?

Answer 29

rhodopsin

Question 30

this absorbs light (using the melanin that is synthesized) that is not absorbed by the photoreceptor cells and thus minimizes reflections of stray light (gets rid of light like how the oval window gets rid of sound after it comes in)

Answer 30

pigment epithelium, digests cones, esterify Vit A, ion transport

Question 31

ganglion cells (innervated by what) of the retina communicate with this structure, thus sending APs down their axons to this structure?

Answer 31

CNII; thalamus (lateral geniculate nucleus); visual cortex

Question 32

this is the center of gaze inside the macula; most of the vision in visual cortex is devoted here

Answer 32

fovea and so each photoreceptor connects to ganglion for CNII in 1:1 ratio for clarity

note that in periphery of retina, maybe 100 or more photoreceptors converge onto one ganglion cell equaling lots of fuzziness in vision going to smaller portions of cortex

Question 33

for signal transduction, when in light our rods depolarize or hyper polarize? what about in dark?

Answer 33

hyper polarize because its usually light and more efficient to not be sending NT every time we need to see

depolarize

Question 34

in terms of signal transduction, what happens in the absence of light?

Answer 34

Na+ enters outer segment of rod thru cGMP gated channels and depolarizes the cell

electrical circuit for this dark current is completed by K+ leaving the inner segment leading to constant transmitter release

Question 35

in terms of signal transduction, what happens in the presence of light?

Answer 35

Na+ can’t enter the cell because cGMP levels are low and cGMP gated channel closes

photoreceptor cell hyperpolarizes and NT releases dec

Question 36

what is the signal transduction pathway?

Answer 36

retinal contains unstable 11 cis retinal form which sits in the pocket of the opsin; this only exists in the dark and appears purple

if it absorbs a photon, it isomerizes to all trans retinal (appears clear) and triggers conformational changes in the opsin leading to metarhodopsin II

after rhodopsin absorbs photon of light transducers are activated, the alpha subunit (G sub at) dissociates from B-gamma subunit and binds to/activates PDE. This hydrolyzes GMP, dec in cGMP gated Na channels leading to hyper polarization

Question 37

what is color vision?

Answer 37

possible only at high light intensities and depends on different spectral properties of rhodopsin in 3 types of cones

S cones - 420 nm smaller

M cones - 520 nm middle

L cones - 560 nm smaller

Question 38

what is the effect of kids looking at iPhones too much?

Answer 38

near-sightedness, need to go outside and look at distant objects in nature

Question 39

this medical condition is when focus point is anterior retina, concave lens, eye too long

Answer 39

myopia-nearsightedness

Question 40

this medical condition is when focus point is posterior to retina, convex lens, eye too short

Answer 40

hyperopia-farsightedness