module 21: vision

VISION SURFACE ANATOMY

what are the eyebrow and eyelashes used for?

they protect the eye from foreign objects, perspiration and help shade eyes from the sun

what do the palpebrae do?

• also known as eyelids lol

• palberbrae - plural

• palabra - singular

• upper eyelid = superior palpebra

• lower eyelid = inferior palpebral

• they shade the eye from light

• protect eye from foreign objects

• spreads lubricant over eyes

what does the palpebral fissure do?

opening for the eye - in between the two palpebrae

what does the commissure do?

this is where the two palpabra meet

what does the medial commissure do??

at the medial commissure we have something known as the crunkcle which contains modified oil and sweat glands they produce the white crust in your eye

what does the lateral caruncle do?

helps with lubrication of the eye

what does the conjunctiva do? 

• mucus lining that forms the inner lining of the eyelid

• blocks things  from getting into the back of the eyelid

what does the palpebral conjunctiva do?

lining of the eyelid

what does the bulbar conjunctiva do?

lining the white of the eye (sclera)

what does the iris do?

the iris is the coloured area of the eye

what does the pupil do?

darken region of the middle iris - acts as a window to let light into the eye

LACRIMAL APPARATUS

please explain the flow of tears

1. the lacrimal gland produces the tears and releases them onto the surface of the eye from the lacrimal ducts

2. the lacrimal ducts which distribute tears over the surface of the eyeball

3. if there is excessive tears this is when they will go into either the puncta from there they will move into the superior or inferior lacrimal canaliculi leading to the lacrimal sac

4. the lacrimal sac will pass tears into the the nasolacrimal duct

5. from the nasolacrimal duct tears will drain into the nasal cavity 

EXTRINSIC MUSCLE OF THE EYE

there are 6 muscle that control the eye what are they??

there are 4 rectus muscles: they all connect to the sclera and extend to to the eye orbit

1. superior rectus muscle

2. inferior rectus muscle

3. medial rectus muscle

4. lateral rectus muscle

there are 2 oblique muscles:

1. superior oblique: runs through the trochlea which acts as a pulley and redirects pull from that muscle allowing for inferior lateral rotation of eye

2. inferior oblique: moves towards the superior lateral side

ANATOMY OF THE EYE

the eye is compressed of 3 tunics what are they?

1. fibrous tunic: white of the eye

• sclera: shape, protection attachment of muscles

• continuous with the cornea - helps us focus light

2. vascular tunic

• choroid: blood supply

• anterior ciliary body and iris

3. retina

• inner most layer of eye

• contains photoreceptors cells

  • cones: we have 6 - 7 million - for colour vision and seeing clearly

  • rods: we have 120 million - low light conditions and black and white

ANATOMY OF THE EYE

what’s the purpose of the sclera?

a tough, thick connective tissue layer that helps maintain the shape of the eye and makes the white portion of the eye

what is the purpose of the cornea?

a transparent, curve-shaped structure that helps the eye focus light

what is the purpose of the vascular tunic?

• contains blood vessels

• contains melanin in the eye

• improves visual acuity

what does the choroid do for the eye?

• provides blood supply

• contains blood vessels

• contains melanin

what do ciliary muscles do for the eye?

• involved in changing the shape of the lens

what do ciliary processes do for the eye?

they are attached to the lens via suspensory ligaments and when the ciliary muscles contract, the tension within the suspensory ligaments will change and alter the shape of the lens

what is the purpose of the iris?

• coloured portion of the eye

• changes diameter and shape of pupil

whats the pupil for?

• the pupil is the dark circle in the middle of the eye

• it acts like a window allowing for light into the eye

what does the sphincter papillae do?

It responds to bright light and is activated by the parasympathetic nervous system to constrict the pupil and make the diameter smaller

what does the dilator papillae do?

when this muscle contracts it increases the diameter of the pupil increases

VISION RETNIA

what is the macula lutea for?

its where we want to focus the light coming into the eye to achieve the greatest visual acuity

what is the optic disk for?

• where the optic nerve and blood supply enter the eye

• there are no photoreceptor cells there creating a blind spot

what are the 2 main layers of the retina what are they?

1. pigmented layer

2. neural layer

what does the pigmented layer do?

• comprised of pigments cells that is full of melanin

what does the neural layer do?

• comprised of 3 layers

• photoreceptors: where we have our rods and cone

• bipolar cell layer:

• ganglion layer:

VISION FOCUSING IMAGES ON THE RETNIA

how do we clearly see an image?

we need to do something called focusing

what is the focal point

where our 2 light rays cross and become inverted

why don’t we see images upsidedown?

the brain will flip those images!

whats the far point of vision?

that is when our lens is flat and the image is about 20ft away

what happens when viewing an image is closer than 20ft?

we have to contract the ciliary ring allowing the lens to be more circular which allows for more focus

what is the near point?

the closest were able to have an object around 4 - 6 inch away from your face

this is where the lens will bend the most

decrease with age

what are the 3 events to bring an image into focus?

1. accommodation: ciliary muscles contract, the lens contracts more and there is greater light refraction

2. pupil constriction: pupil diameter gets smaller - greater depth focus

3. convergence: as objects get closer we need to rotate our eyes medially in order to pick up those light rays

VISON - PHOTORECEPTORS

what are rod cells used for?

• rhodopsin

• no colour vision

• low light conditions

what is rhodopsin made out of?

retinal and opsin

what are cone cells used for?

• colour vision

• high light

• iodopsin

what is iodopsin made out of?

retinal and red, blue and green opsin