eye

Protection for the eye

Most of the eye is enclosed in a bony orbit

A cushion of fat surrounds most of the eye

accessory structures of the eye

eyebrows, eyelids, conjunctiva, lacrimal apparatus, extrinsic eye muscles

eyelids

meet at the medial and lateral commissure

eyelashes

-Tarsal glands produce an oily secretion that lubricates the eye

-Ciliary glands are located between the eyelashes

conjunctiva

membrane that lines the eyelids

connects to the surface of the eye

secretes mucus to lubricate the eye and keep it moist

conjuctivitst is inflammation of the conjunctiva results in red irritated eyes, caused by a virus or bacteria very contagious

inflammation can be caused by dust

lacrimal apparatus

lacrimal gland and ducts that drain into nasal cavity

lacrimal gland

produce lacrimal fluid, situated on lateral aspect of each eye

lacrimal canaliculi

drain lacrimal fluid from eyes medially

lacrimal sac

provides passage of lacrimal fluid towards nasal cavity

nasolacrimal duct

empties lacrimal fluid into the nasal cavity

function of lacrimal apparatus

Protects, moistens, and lubricates the eye

Empties into the nasal cavity

lacrimal secretions contain

dilute salt solution, mucus, antibodies, lysozyme

extrinsic eye muscles

6 muscles attach to the outer surface of the eye and produce eye movements

these muscles are controlled by cranial nerves 3, 4, 6

Structure of the eye

ensor-Layers forming the wall of the eyeball:

fibrous layer

outside layer

vascular layer

middle layer

sensory layer

inside layer

humors are fluids that fill the interior of the eyeball

the fibrous layer

sclera and cornea

Sclera

• White connective tissue layer
• Seen anteriorly as the "white of the eye"

Cornea

transparent, central anterior portion

allows for right to pass through

repairs itself easily

the only human tissue that can be transplanted without fear of rejection

vascular layer

choroid is a blood rich nutritive layer in the posterior of the eye

modified anteriorly into 2 structures

ciliary body

smooth muscle attached to lens by ciliary body-smooth muscle attached to lens by ciliary zone

iris

regulates the amount of light entering the eye

pigmented layer that gives eye color

pupil

rounded opening in the iris

sensory layer

retina contains two layers

1. outer pigmented layer absorbs light and prevents it from scattering
2. inner neural layer contains receptor cells (photoreceptors)

rods

cones

outer pigmented layer

absorbs light and prevents it from scattering

inner neural layer

Contains receptor cells (photoreceptors)

rods

cones

Rods

retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when cones don't respond

Cones

allows for detailed color vision

dense in the center of the retina

fovea centralis

lateral to blind spot

-Area of the retina with only cones

lens

biconvex crystal like structure

held in place by a suspensory ligament attached to the ciliary body

cataracts result when the lens beep,es hard and opaque with age

2 segments or chamber of the eye

lens divide the eye into two chamber

Anterior (aqueous) segment

anterior to the lens, contains aqueous humor

Posterior (vitreous) segment

posterior to the lens, contains vitreous humor

aqueous humor

water fluid found between lens and cornea

similar to blood plasma

helps maintain interocular pressure

reabsorbed into venous blood through the scleral venous sinus (canal of schleming)

posterior segment

contains vitreous humor

vitreous humor

jellylike substance found behind the lens in the posterior cavity of the eye that maintains its shape

ophthalmo scope

instrument for examining the eye

can detect diabetes, arteriosclerosis, degeneration of the optic nerve and retina.

Pathway of light through the eye

Light enters eye -> cornea -> aqueous humor -> lens -> vitreous humor -> neural layer of retina

accommmodation

the lens mist change sable to focus on closer objects

real images are

reversed from left to right, upside down, smaller than the object

visual field and visual pathways

optic charisma and optic tracts

optic charisma

location where the optic nerves cross

fibers from the medial side of each eye brass over to the opposite sides of the brain

optic tracts

contain gibers from the lateral side of the eye on the same side and the medial side of the opposite eye.

emmetropia

focuses imaged correctly on the retina

Myopia (nearsightedness)

a condition resulting from a refractive error in which light rays entering the eye are brought into focus in front of the retina.

Hyperopia (farsightedness)

a refractive error in which light rays entering the eye are focused behind the retina.

astigmatism

Images are blurry

Results from light focusing as lines, not points, on the retina due to unequal curvatures of the cornea or lens

night blindness

inhabited rod function that hinders the ability to see at night

color blindness

genetic conditions that result in the ability to see certain colors

Glaucoma

can cause blindness due to increasing pressure within the eye

macular degeneration

causes vision loss and is an incurable eye disease, the center portion of the retina degenerates caused by genetics

Canal of Schlemma

the scleral venous sinus