Structure and function of the eye

Question 1

What are the 3 main bones of the orbit?

Answer 1

Lacrimal bone, ethmoid bone and frontal bone

(many holes at back-mainly superior orbital fissure

Question 2

What is the space between the two eyelids? and the most lateral corner of the eye? What structure do you find in the medial canthus?

Answer 2

Palpebral fissure
Lateral canthus (the medial one is medial canthus
Caruncle

Question 3

In the eye, how do you call the black center, coloured part and the white part? And the limit between the iris and sclera?

Answer 3

Pupil, iris, sclera

Limbus-limit between cornea and sclera, where stem cells lie

Question 4

What keeps the eye wet?

Answer 4

Lacrimal system

Question 5

What produces the tears in the lacrimal system?

Answer 5

Lacrimal gland above eye produce the tears, and they go to the eye. Then through caruncle, to canaliculi to tear sac and to nose

Question 6

What is tear film and its use?

Answer 6

Maintain smooth cornea air siface-thin film of tars (lipid layer, water layer and mucin layer -siting on microvillia cells)-applied when we blink
Provides oxygen to cornea, clears debris

Question 7

What is the conjungtiva? Where does it lie? What is it blood supply?

Answer 7

Thin transparent tissue that covers outer eye -begins at the outer edge of cornea and covers visible eye, and lines the inside of eye lids (Cant slip anything undereyelid)
Blood supply from tiny blood vessels that are invisible to naked eye (except if pathology, like conjungtivitis)

Question 8

What muscle do you find around the eye?

Answer 8

Cilliary bodies around the lens modify its shape

Rectus muscle connect to cornea (on the outside)-move eye up and down

Question 9

What are the exterior (to interior) layers of the eye? What are their main charateristics?

Answer 9

Sclera-hard and opaque-high water content (non sharp object hitting eye will break bone before eye)
choroid-pigmented and vascular
retina-neurosensory tissue

Question 10

How does the cornea relate to the sclera? What is the cornea?

Answer 10

Transparent, dome shaped window. Continuation of the cornea-2/3 focusing power of the eye –low water content
Front-most part -also physical and infection barrier

Question 11

What are the 5 layers of the cornea?

Answer 11

Epithelium-bowmans membrane, stroma (thick transparent), descemet’s membrane, endothelium (decrease with age)
Its pretty musch stroma sandwiched by cells, and their basal membrane (weird names)

Question 12

What is the Uvea? What is it composed of?

Answer 12

vascular coat of eye ball-3 parts–Iris, cilliary body and choroid
They are connected and diseases of one can affect the others - can differentiate between disease of anterior/middle posterior diseases by seeing where opaque liquid is

Question 13

What is the choroid?

Answer 13

Lies between of the retina and sclera, and composes of layers of blood vessels that nourish the BACK of the eye

Question 14

What is the iris?

Answer 14

Anterior part of the Uvea-controles light levels inside the eye. The opening in the center is called the pupil
Muscle around dilate and contrict iris
Controls luminosity and depth of field

Question 15

What is the lens? How does it change it shape?

Answer 15

Acellular capsule made mostly of collagens-regular elongated cell fibres (cataract if lose transparency)
Important refractive power (1/3 of eye)-
Elastic, so can accomodate-shift the focus by distorting its shape
Cilliary muscle connect to lens, which is suspended by fibrous rings nown as zonules by them. They can modify (pull/push). When contract, push the zonules closer and thicken lens

Question 16

What is the retina?

Answer 16

Very thin layer of tissue that lines inner eye

Responsible for capturing light rays -and send them to the brain via the optic nerbe

Question 17

What is the optic nerve?

Answer 17

Transmits electrical signal to brain from eye

Connects to eye near macula-at the back of the eye-visible part is called optic disc

Question 18

What is the macula?

Answer 18

Located roughly center of retina-temporal to optic nerve
Small and highly sensitive part of retina-detailed central vision-like reading
Center called the fovea-highest amount of cones and good ration of ganglionic cells to photoreceptors (lowest amount of rods-)

Question 19

What are the two anatomical segments of the eye

Answer 19

Anterior segment-between cornea and less-filled with clear aqueous fluid
Posterior segment-between lens and rest of eye

Question 20

What can you find within the cilliary bodies>

Answer 20

Cilliary muscles at the back, but also secrete aquerous fluid of the eye
Flows towards anterior chamber-along the iris, via pupil
Supplies the nutrients-the oxygen is gotten rom air
Trabecular meshwork drains the fluid out-via canal of schlemm (80%-rest is aborbed)

Question 21

What is glaucoma?

Answer 21

Sustained rise of intraoccular pressure-risk factor (if anything pressures the eye, higher chance to damage the rest)
Retinal ganglion cell death and optic disc cupping-visual field loss, blindness
Eye is closed structure, so either reduce prod or increase drainage
–will lose part of vision, but brain fills the gap-so sometimes would just miss out of cars coming)

Question 22

What are the different types of glaucoma?

Answer 22

Primary open angle glaucoma (commenest)-trabecular network dysfunction
Closed angle glaucoma-acute or chronic

Question 23

What are the differences between blood vessels you can see in the ey?

Answer 23

veins are thicker and darker, arterioles are smaller and thinner

Question 24

What is the optic nerve blind spot?

Answer 24

So specialised-doesnt have photoreceptors

So imaged on the nerve doesnt reach the brain

Question 25

What is the difference bewteen central and peripheral vision>

Answer 25

Detailed day vision, colour-redaing facial, assessed via visual field assessment-if lost poor acuity)
Peripheral-shape, movement, night vision -navigation vision
assessed via visual field assessment -if lost-cant navigate well

Question 26

Describe the layers of the retina?

Answer 26

Important-LIGHT BOUNCES ON RETINA BEFORE BEING DETECTED-MEANING PHOTORECEPTORs ARE ACTUALLY FACING INWARDS TOWARDS RETINA
So “outer layer”-photoreceptors (1st order neurons)-connect to bipolar cells in “middle layer”-local signal processing, then to axons of optic nerve (3rd order neurons) in the “inner layer” (thats the one most outwards tho)

Question 27

What are the 2 types of photoreceptors? how are they distributed

Answer 27

2 types-rods and cones
Rods are longer, and 100 times more sensitive to light, but slow response and no colour. Have 120m
Cones-less sensitive, but faster, and colour-
Cones are very high in center (fovea) and thats pretty much it)-cones are all around, except in blind spots (highest conc between 20 and 40 degrees)

Question 28

How do cones and rods differ on the light frequency they can see?

Answer 28

S cones-blie, rods-black, M cones-green, L cones-red

Eye can see 400-700 nm(700 is red).

Question 29

What are different types of color vision deficiencies? how do you test

Answer 29

Normal-deuteuranomaly (daltonism)-red green confusion, and other
Test with ishihara test (the numbers in the coloured circle)

Question 30

How do cones and rods adapt to the dark and light?

Answer 30

In the dark-cone adapt in 7mins, rods in about 30-biphasic process. rods are more sensitive after a bit of time and lower light
Light adapation-occurs over 5minutes-neurological adaptiation-inhbition of rod/cones
Also pupil also acts

Question 31

What is refraction?

Answer 31

Passing of light from one medium to another changes the speed (the denser the medium, the slower)_the slowing causes an angle change -refraction index =speed in vac/speed in medium.
Convex lens bring all the light to converge on a point-focal point (concave diverge light). focal length is distance between lens and focal point

Question 32

What is emmetropia? and Ametropia?

Answer 32

Adequate correlation between axial length and refrative power (NORMAL EYE SIGHT)
Amtropia-mismatch between axial length and refractive power
eg: Myopia (near sighted)-rays focal point too early (eye ball can be to long (commonest), or lens is to convex, or cornea too convex -cant see far, squint a lot (get only central one cause that one doesnt refract)-use glasses, contact or surgery on cornea (flatten in)
hyperopia (long sighted)-rays focal point too late - (eye too short, lens or conea too concave)-if left untreated for a while in one eye-brain will start ignroing it-irreversible
treat with glasses, contacts
Astigmatism-rays focuses in 2 focal line rather than 1 point-caused by refractive medial not perfrctly spherical-one side of the lens is wrong-refreact differently alongon meridian–some objects will appear blurry-treat it with shperical lens- will generate all focus at one point-cylinder lens tried to match and compensate
Presbypia-lens gets stiffer with age-loss of accomodation, usually for close objects-treated with concave lens, contact lenses

Question 33

WHat is myopia?

Answer 33

eg: Myopia (near sighted)-rays focal point too early (eye ball can be to long (commonest), or lens is to convex, or cornea too convex -cant see far, squint a lot (get only central one cause that one doesnt refract)-use glasses, contact or surgery on cornea (flatten in)

Question 34

What is hyperopia?

Answer 34

hyperopia (long sighted)-rays focal point too late - (eye too short, lens or conea too concave)-if left untreated for a while in one eye-brain will start ignroing it-irreversible
treat with glasses, contacts

Question 35

What is astrigmatism?

Answer 35

Astigmatism-rays focuses in 2 focal line rather than 1 point-caused by refractive medial not perfrctly spherical-one side of the lens is wrong-refreact differently alongon meridian–some objects will appear blurry-treat it with shperical lens- will generate all focus at one point

Question 36

What is presbypia?

Answer 36

Presbypia-lens gets stiffer with age-loss of accomodation, usually for close objects-treated with concave lens, contact lenses, intraocular lenses, surgery, fake lens impant