eye anatomy

what is an external structure that houses the eye?

bony orbit

where is the bony orbit located in?

the frontal bone of the skull

how many bones is the bony orbit composed of?

7 bones

what are the 7 bones of the bony orbit?

frontal, sphenoid, ethmoid, super maxillary, zygomatic, lacrimal, and palate

what is the bony orbit lined with?

fatty tissue for cushion

why is the rim of the bony orbit thicker?

for protection of the eye

extrinsic muscles

each is associated with one primary movement, functions to move the eye in various directions and helps focus them together, 4 rectus and 2 oblique

what are the 4 rectus extrinsic muscles?

superior, inferior, lateral, and medial

what are the 2 oblique extrinsic muscles?

superior and inferior

conjunctiva

thin, transparent mucous membrane that lines the eyelids

eyelids

2 musculofibrous folds in front of each orbit, protects the globe and eye from light, injury and dust, and distributes lacrimal secretions

canthus

inner and outer corner of eye where eyelids meet

lacrimal caruncle

small, pink tissue mass at inner corner

lacrimal apparatus

produces and secretes tears thru a series of ducts into the conjunctival sac, contains lacrimal gland, lacrimal, ducts, lacrimal punctum, and lacrimal sac

lacrimal gland

secretes tears

lacrimal ducts

12 separate ducts that carry tears from inner canthus to the lacrimal sac

lacrimal punctum

opening of duct

lacrimal sac

larger opening at the upper end of the nasolacrimal duct, drains into the nose

what are the 3 layers the internal structures are divided into?

external (corneoscleral), middle, and inner

what is included in the external layer of the internal eye structures?

cornea and sclera

what is included in the middle layer of the internal eye structures?

choroid, ciliary body, iris, and pupil

what is included in the inner layer of the internal eye structures?

retina, optic disc, and macula

what are the internal structures of the eye?

cornea, sclera, choroid, ciliary body, iris, pupil, retina, optic disc, and macula

cornea

fine, transparent membrane covering the front of the eyeball (anterior), joins the sclera at the limbus, contains 5 layers, and is termed the “window of the eye”

why is the cornea termed the “window of the eye”?

because it allows light rays to pass to retina

sclera

encompasses the back ¾ of eyeball (posterior), made of collagenous fibers and fascia, it is opaque white, an extension of the cornea, and provides support to the eye

choroid

contains many blood vessels, main source of eye nourishment, and prevents reflection of light within eyeball

ciliary body

extension of the choroid layer, made of muscle tissue, forms the aqueous humor, and affects accommodation (focusing) of the eye

iris

lies in front of the lens and behind the cornea, colored part of the eye, composed of muscle tissue, radial and circular fibers, and regulates amount of light entering eye

pupil

opening in center of iris, dilates and constricts

retina

thin, transparent, many-layered membrane, photoreceptive layer of eye, rods and cones, sensory neurons, nerve fibers converge to become the optic nerve responds to light energy (receives images and sends to brain via optic nerve)

optic disc

where the optic nerve enters the eye (blind spot)

macula

yellow spot in center of retina, fovea centrialis contained here, and area of highest resolution and central vision

fovea centralis

tiny, depressed area containing only cones

what does the refractive apparatus contain?

cornea, anterior chamber, lens, and vitreous body (posterior chamber)

refractive function of the cornea

has the greatest refractive power of all the eye structures, bends light rays (affects visual acuity), variations in curve of cornea affects visual acuity (myopic and hyperopic)

myopic

nearsighted

hyperopic

farsighted

anterior chamber

lies in front of the iris (anterior), filled with aqueous humor, has canal of schlemm, and glaucoma occurs here

canal of schlemm

drains excess fluid into the venous system

glaucoma

when the duct doesn’t work, fluid backs up, results in increased pressure in eyeball which can lead to blindness

lens

suspended behind the iris and connected to the ciliary body by zonular fibers, reflects light to retina (accommodation), biconvex (1cm diameter), it is clear and surrounded by a capsule, a cataract occurs here

cataract

cells compress and harden with age and become cloudy and opaque

vitreous body (aka vitreous humor) (posterior chamber)

transparent, gelatinous mass, composed of 99% water, 1% collagen, and hyaluronic acid, fills the posterior 4/5th of eyeball, adheres to the retina, and maintains shape of eyeball

nerves and blood supply to the eye include

optic nerve, oculomotor nerve, trochlear nerve, abducens nerve, ophthalmic artery, and central retinal artery and vein

optic nerve

2nd cranial nerve, carries visual impulses to the brain, sends sensations of pain, touch, and temperature of the eye to the brain

oculomotor nerve

3rd cranial nerve, primary motor nerve to all except one rectus muscle, and moves eyeball and constricts pupil

trochlear nerve

4th cranial nerve, innervates the superior oblique muscle

abducens nerve

6th cranial nerve, innervates the lateral rectus muscle

ophthalmic artery

main arterial supply to the orbit and globe, branch of the internal carotid artery

central retinal artery and vein

travels thru optic nerve, provides independent circulation for the inner retina

OD

right eye

OS

left eye

OU

both eyes

applanation tonometry

diagnose glaucoma by measuring the amount of pressure needed to flatten a portion of the cornea

corneal and retinal topography

specialized computerized tests used to create a “map” of the curvature of the cornea or surface of the retina, can show distortions of the surface of the eye, such as swelling or scarring, as well as conditions such as astigmatism

fluorescein angiogram

evaluate the blood circulation in the retina, useful in helping diagnose diabetic retinopathy, retinal detachment, and macular degeneration

dilated pupillary exam

drops in the eye that cause the pupil to dilate, doctor can examine your retina for any signs of disease

refraction

determines your eyeglasses prescription

slit-lamp exam

looks at the eye with a microscope shining a beam of light shaped like a small slit on the eye, used to help diagnose cataracts, glaucoma, retinal detachment, macular degeneration, injuries to the cornea, and dry eye disease