lecture 32 eye

pyramidal cavity with its apex directly posteriorly

what is the orbit?

5/6

the orbit contains the eye and protects what fraction of it?

superiorly-frontal bones

inferomedially-maxillae

inferolaterally-zygomas

what are the borders of the eye orbit?

frontal bone

what is the roof of the orbit?

zygoma and greater wing of sphenoid

what is the lateral wall of the orbit?

maxilla

what is the floor of the orbit?

maxilla, lacrimal, ethmoid, sphenoid, and palatine bones

what is the medial wall of the orbit?

sphenoid bone

what is the optic canal is surrounded by?

1. fibrous tunic or external coat

2. vascular tunic or middle coat

3. nervous tunic or internal or retinal coat

what are the three tunics or layers of the eyeball?

fibrous tunic (or external coat)

what is the outermost covering of the eyeball?

sclera and cornea

what is the fibrous tunic composed of?

tough, fibrous, opaque, white portion of the eyeball that is visible around the margins of the eye

what is the sclera?

about 5/6

what fraction of the eyeball does the sclera cover?

optic nerve and associated vessels

what does the sclera have perforations for?

two (one for optic n and one for cornea)

how many openings does the sclera have?

clear, transparent, anterior portion of the fibrous tunic

what is the cornea?

1/6

what fraction of the eyeball does the cornea compose?

avascular

is the cornea vascular or avascular?

refracts light as it enters the eyeball

what is the function of the cornea?

takes longer to heal, needs nutrients from other sources (normally via diffusion)

what is the clinical significance of the cornea being avascular?

choroid, ciliary body, iris, pupil

what makes up the vascular tunic or middle coat?

highly vascular layer deep to sclera

what is the choroid?

supplies blood to outer layer of retina

what is the function of the choroid?

anterior continuation of choroid that is composed of smooth muscle

what is the ciliary body?

extension from ciliary body, pigmented epithelium backed with smooth m

what is the iris?

diaphragm that separates the anterior chamber from the posterior chamber

what does the iris form?

circular smooth m that constricts pupil

what is the sphincter pupillae?

radial smooth m that dilates the pupil

what is the dilator pupillae?

opening within iris

what is the pupil?

1. pigmented epithelial layer

2. photoreceptor or neural layer

what are the two layers of the nervous tunic (internal or retinal coat)?

single layer of cells rich in melanin that decreases the scatter of intraocular light

describe the pigmented epithelial layer of the nervous tunic

pigmented epithelial layer of nervous tunic

what is the outer layer of retina?

contains rods and cones which are bipolar neurons

describe the photoreceptor or neural layer of the nervous tunic

120 million

how many rods are present in the photoreceptor or neural layer?

light

what are rods sensitive to?

rods

what are responsible for night vision?

6-7 million

how many cones are present in the photoreceptor or neural layer?

2/3 sensitive to red, 1/3 sensitive to green, 2% sensitive to blue wavelengths

what are cones sensitive to?

optic n, ora serrata, macula lutea, fovea centralis

what are the specializations of nervous tunic?

medial to posterior pole

where does the optic nerve exit?

no photoreceptors, central retinal a, v

what does the optic disc contain?

serrated anterior margin of the retinal coat

what is the ora serrata?

yellow region, posterior pole, lateral to optic disc

what is the macula lutea?

located in center of macula, most sensitive portion of retina, area of most acute vision

what is the fovea centralis?

densely packed cones and no rods

what does the fovea centralis contain?

fovea centralis

when looking directly at an object, the image of the object is focused on what?

cones

what are located in the macula lutea but are most highly concentrated in the fovea centralis?

very intense

cones are sensitive to bright light (daylight) situations in which light is...

a single bipolar cell which synapses with a single ganglion cell

what does each cone synapse with?

axons of ganglion cells

what forms the optic nerve to conduct visual images to the brain?

acute (sharp) color images (vision)

what do cones provide?

retina outside macula lutea

where are rods most highly concentrated?

many rods synapse with single bipolar cell (convergence)

describe interaction between rods and bipolar cells

rods (s)

are rods or cones more sensitive?

dim light, night, and peripheral vision

rods function only in...

blurry and in shades of gray

what kind of images do rods produce?

cones are significantly smaller

how do the sizes of cones and rods compare?

transparent, biconvex structure that is flexible, avascular

what is the lens?

suspensory ligaments

what can modify the shape of the lens?

lens

what separates the anterior cavity from the posterior cavity?

suspensory ligaments (ciliary zonule)

what is the lens held around its circumference by?

change in refraction of image

what does the lens allow for?

anterior cavity (anterior to lens)

where is the aqueous humor located?

epithelial cells projecting from ciliary body

what is aqueous humor produced by?

scleral venous sinus (canal of Schlemm)

aqueous fluid flows from the posterior to anterior chamber and into what?

posterior cavity (posterior to lens)

where is vitreous humor or body located?

refracting media of eye

what are the structures that bend light rays called?

cornea, aqueous humor, lens, vitreous humor

what makes up the refracting media of the eye?

cornea

what is the primary refractor of the eye?

point of contact between upper and lower eyelids

what is the palpebral fissure?

angle of the eye, point where upper and lower eyelids meet

what is the lateral and medial canthus?

mound of tissue at medial canthus and containing glands

what is the lacrimal caruncle

dense band of CT within each eyelid

what is the tarsal plate?

tarsal glands

what glands are embedded within the tarsal plate?

modified sebaceous gland that emits an oily secretion

what are the tarsal glands?

prevents eyelids from sticking together when closed, reduces evaporation, prevents overflow of tears, and helps make the closed eyelids airtight

what are the functions of the secretions of the tarsal glands?

epithelium forming mucous membrane that lines the inner surface of the eyelids and covers the cornea

what is the conjunctiva?

produces mucous that lubricates the eye and prevents dryness, protects the eye

what is the function of the conjunctiva?

palpebral conjunctiva

what lines the eyelids?

bulbar or ocular conjunctiva

what lines the cornea?

recess formed by palpebral conjunctiva, point of reflection of conjunctiva

what is the conjunctival fornix?

space between palpebral and bulbar conjunctiva

what is the conjunctival sac?

lacrimal fluid (tears)

what does the lacrimal gland produce?

superolateral part of the orbit

where is the lacrimal gland located?

3 to 12 ducts

what opens into the superior fornix of the conjunctival sac?

lacrimal gland, tear ducts, lacrimal puncta, lacrimal canaliculi, lacrimal sac, nasolacrimal duct, inferior meatus

what are the components of the lacrimal apparatus?

opening on upper and lower eyelids near medial canthus that leads to lacrimal canaliculus

what are the lacrimal puncta?

Small canals extending and carrying tears from punctum to sac

what are lacrimal canaliculus?

dilation of superior end of duct which receives canaliculi

what is the lacrimal sac?

from sac to nasal cavity where it ends

where does the nasociliary duct extend from and to?

basal tears, reflex tears, psychic or emotional tears

what are the different types of tears?

most common, smooth out irregularities of the cornea allowing for vision as we know it

describe basal tears

stream after a poke in the eye or whiff of an onion

describe reflex tears

accompany emotional trauma, fear, joy, and especially sadness trigger tears

describe psychic or emotional tears

emotional tears and reflex tears

what type of tears have different chemical compositions?

epinephrine

what do emotional tears have excess of after a traumatic event?

3, 6

the eye moves about ___ axes resulting in ___ movements

abduction, adduction, elevation, depression, intortion, extortion

what are the 6 movements of the eye?

medial rotation

what is intortion?

lateral rotation

what is extortion?