7 Bones that form the Orbital Walls of the Skull
Roof: Frontal Bone
Lateral Wall: Zygomatic Bone
Floor: Maxillary Bone
Medial Wall: Lacrimal and Ethmoid Bone
Back Wall: Greater wing of Sphenoid Bone and Palatine Bone
The Frontal Bone...
contains the frontal sinuses.
The Zygomatic Bone...
rarely gets damaged.
The Maxillary Bone...
is the most common spot for an orbital fracture (blunt force trauma)
Blowout Fracture
orbit contents herniate downward into the underlying maxillary sinus
Enopthalmia
sunken-in eyeball position and inferior rectus muscle entrapment
The Lacrimal Bone...
has nasolacrimal canal passing through it.
The Ethmoid Bone...
is the thinnest part of the bony orbit and is also called the lamina papyracea
rarely fractures
Orbital Cellulitis
most common in kids
severe sinus infections can erode through the ethmoid bone and
create this condition
Basic functions of the Eyebrows
facial expression
shades the eyes from sunlight
prevents perspiration from trickling down the forehead and
entering the eye
Corrugator Supercilii Muscle....
moves eyebrows together. (medially)
Accessory Structures of the Eye
Eyelids
Lacrimal Caruncle
Epicanthic Folds
Tarsal Glands
Ciliary Glands
Levator palpebrae superioris
Orbicularis Oculi
Conjunctiva
Eyelids
AKA Palpebrae
The Palpebral Fissure...
is the opening between eyelids.
Eyelids meet medially and laterally at the...
medial and lateral commissure (canthus)
The Lacrimal Caruncle is...
the "elevated bit of flesh", found at the medial canthus
and lets tears and oil out
Epicanthic Folds are...
vertical skin folds covering the medial commissure
ex: Asian faces, Down Syndrome, Fetal Alcohol Syndrome, Pre-term
Tarsal Glands
AKA Meibomian Glands
modified sebaceous gland located underneath and inside the tarsal plates
makes closed lids airtight
There are duct openings in the tarsal glands that...
secrete oily substances to keep the eyelids from sticking together
and prevent tear film evaporation.
Chalazion
clogging of tarsal glands causing lipids to back up in the gland and
cause a non-infectious inflammatory granuloma reaction which is
usually painless and chronic
Ciliary Glands...
are sebaceous glands and modified sweat glands found between
eyelashes and superficial to the tarsal plate
Stye (Sty)
infection or blockage of ciliary glands
To open the eyelid...
use the Levator palpebral superioris muscle
cranial nerve III-Oculomotor nerve
Damage to the Oculomotor Nerve-CN III causes...
Ptosis.."Droopy Eyelid
To close the eyelid and depress the eyebrows...
use the Orbicularis oculi muscle
CN VII- Facial Nerve
We blink every...
3-7 seconds to protect our eyes
Tears are formed in the...
lacrimal gland
In what direction do tears flow?
medially
Path of Tears
from the lacrimal gland to the lacrimal puncta (openings of lacrimal
canaliculi), lacrimal sac, nose through the nasolacrimal ducts and the
inferior nasal meatus
Lysozyme is...
an enzyme that destroys bacteria
Lacrimal Fluid contains...
mucus, antibodies, and lysozyme
The Conjunctiva is...
a thin, transparent mucous membrane that lubricates eye
(where eye meds or contacts go)
Palpebral Conjunctiva...
lines and coats lids.
Bulbar Conjunctiva...
covers the sclera (white of the eye), but not the cornea
Conjunctival sac...
the space created by the fold of the palpebral over the bulbar
Pink eye is found where?
the conjunctiva (as in conjunctivitis)
Extrinsic Eye Muscles
4 rectus muscles
2 oblique muscles
All 6 extrinsic muscles insert...
on the eyeball surface.
The 4 rectus muscles originate...
from a common tendinous ring at the back of the orbit: the annular
ring (aka common tendinous ring)
The Superior oblique originates...
from the same spot as the 4 rectus muscles and is the only eye muscle
to pass through the trochlea.
The Inferior oblique originates...
from the medial orbit surface.
The superior and inferior rectus muscles pull the eye...
a bit medially and need the obliques to cancel that movement out so
you can look straight up or down.
The 6 Extrinsic eye muscles have highest precision of the skeletal muscles...
because of the high axon-to-muscle-fiber ratio with the motor units
of these muscles containing 1 nerve axon for every 2 to 12 muscle cells.
Ocular Alignment Medical Problems
Strabismus (Cross-eyed)
Diplopia (double vision)
Common in acute alcohol intoxication
diplopia (double vision)
Binocular vs. Monocular Diplopia
Monocular is present if...
it stays after covering one eye
(refractive error)
Examples of a refractive error
astigmatism
cataract
lens displacement
corneal surface wrinkling
Binocular vs. Monocular Diplopia
Binocular is present if...
the eyes don't move together in sync
Examples of Binocular Diplopia...
cranial nerve lesions (CN3, CN4,CN6)
muscle fibrosis in Grave's Disease
Neuromuscular--Myasthenia Gravis
Strabismus
congenital weakness of extrinsic eye muscles
tested by corneal light reflex and cover test
Treatment for Strabismus
patch on strong eye or surgery
The Corneal Light Reflex test: When the light reflex is not in the
center, it could be from...
a short medial rectus (keeping the right eye looking straight ahead)
due to congenital strabismus
OR
a weak lateral rectus (the stronger medial rectus overpowers it)
due to right CN VI palsy or alcohol intoxication (double vision)
CN III: Oculomotor Nerve Palsy
Muscles that do not work...
superior rectus
inferior rectus
medial rectus
inferior oblique
levator palpebrae superioris (leads to eyelid ptosis)
pupillary constrictor (leads to blown pupil)
CN III: Oculomotor Nerve Palsy
Muscles that work...
superior oblique pulls gaze
lateral rectus pulls gaze laterally
Left Abducens (CN VI) Palsy
possibly from an aneurysm
symptoms: affected eye's gaze drifts inward, diplopia
(pressure)
All 6 of the extrinsic eye muscles are the most rapidly and precisely
controlled skeletal muscles in the entire body because of the...
high axon-to-muscle-fiber ratio with the motor units of these muscles
containing 1 nerve axon for every 2 to 12 muscles.
The 3 Layers of the Eyeball are...
Fibrous
Vascular
Inner Layer
Fibrous Layer has...
2 avascular regions:
the sclera
the cornea
Pressure of cornea checked with a...
Goldman Tonometer
The outer side of the cornea is made out of...
stratified squamous epithelium, for protection
The inner side of the cornea is made out of...
simple squamous epithelium
Vascular Layer AKA "Uvea" contains the...
choroid plexus
ciliary body
iris
pupil
Choroid Plexus jobs
its blood vessels bring nutrition to all eye layers, especially the retina
its brown pigment from melanocytes help absorb light
Ciliary Body is a ...
round sphincter-like muscle AKA "ciliary muscle
To read close-up, the eye has...
the Ciliary Body that contracts to relax its zonules, allowing the
lens to become rounder and increase the refractive power
The iris is made up of...
smooth muscle and elastic fibers.
can be used for ID of a person
Dilator Pupillae is activated by...
Sympathetic activation of the CN V1.
The fibers of the dilator papillae are...
radial.
The fibers of the sphincter papillae are...
circular.
Excessive dilation of the eye is called...
Mydriasis.
Dilated pupils are used for...
distant vision and dim light
problem solving
LSD
Marijuana
Ecstacy
Cocaine
Mushrooms
Crystal Meth
Intense Emotional Excitement (Fight or Flight)
Sexual Arousal
Extensive constriction is called...
Miosis.
The sphincter papillae muscle (constriction of the eye) is activated by...
Parasympathetic activation of the CN III.
Constricted pupils are used for...
close vision
bright light
boredom
opiates
heroin
morphine
sleep
The wall of the eyeball has...
3 layers
Inner layer of the eye consists of...
the outer pigmented layer and inner neural layer
The outer pigmented layer is a...
single-cell-thick layer of pigmented cells that absorb light and
prevent its scatter
The inner neural layer jobs
plays a direct role in vision
The outer pigmented layer jobs
acts as phagocytes to remove damaged photoreceptors
stores vitamin A (used by photoreceptor cells)
The inner neural layer has 3 neuron layers...
photoreceptor cells
bipolar cells
ganglian cells
Ora serrata is...
a junction of the inner neural layer and the posterior margin of the
ciliary body.
Neovascularization is a process that entails...
capillary wall thickening and destruction
injured capillaries leak their contents into the layers of the retina
damaged vessels and starved tissues release VEGF to promote new,
fragile, dislocated blood vessels to grow
could cause new bleeds
Diseases such as hypertension and diabetes can cause...
neovascularization.
The most common cause of blindness in diabetes is..
macular edema.
Macular Edema is...
repeated, localized capillary damage and leakage from
neovascularization, causing the macula lutea to swell with fluid and elevate
Treatment for Neovascularization and Macular Edema...
Argon Laser-to seal leaky vessels
Pan-Retinal photocoagulation-to destroy ischemic retinal tissue
and reduce wrong responses
Vitrectomy and replacement with saline
Incidence of Retinal Detachment
1 in 10,000 people
common in blunt force trauma or after surgery
Symptoms of Retinal Detachment
flashes of light (photopsias) and floaters (swarm of flies)
dark curtain from peripheral to central
3 types of Retinal Detachment
Rhegmatogenous
Traction
Hemorrhagic or Exudative
Tear through the retinal layers
Rhegmatogenous
Retina is pulled off by neovascularization or vitreous humor
Traction
Blood or fluid build up that pulls retina off
Hemorrhagic or Exudative
Fully detached retinas will still be attached to...
the ora seratta and optic disk
Treatment of Retinal Detachment
tack down with argon laser burns
scleral buckling (squeezing)
pheumatic retinopexy (uses gas or oil bubble)
Inner Layer: Fundus consists of...
the optic disk and macula lutea
The optic disk is the...
blind spot" or weak spot on the fundus
lacks photoreceptors
cupping increases and dies during glaucoma
Macula Lutea AKA "Yellow Spot" has a tiny pit in its middle called...
the Fovea Centralis
The Fovea Centralis has...
Cones.
The best visual acuity
The Fundus is the only place where...
small blood vessels can be observed directly in a living person, with
an ophthalmoscope
The Choroid and Central Artery/Vein
gives the most blood supply to the eye
Choroid job
supplies photoreceptors-rods and cones
Central Artery and Vein job
suppose the bipolar and ganglion cells layers of the fundus
Floaters can get stuck where in the eye?
the vitreous humor
The posterior segment holds the ...
vitreous humor.
The Anterior segment holds the...
anterior chamber
posterior chamber
aqueous humor
Aqueous humor is...
a clear fluid similar to that of blood plasma
Aqueous humor jobs
supplies nutrients and removes metabolic wastes
forms, circulates, and drains continuously
Aqueous humor exits...
by the canal of schlemm
Glaucoma is where...
the optic nerve dies from too much intraocular pressure
Open-angle (chronic) Glaucoma
more gradual
most common type
caused by clogging of trabecular meshwork
ganglion cell and optic nerve atrophy
Peripheral Scotomas..
areas of visual field loss
treatment for open-angle glaucoma
eye drops to reduce aqueous humor production or increase the aqueous
humor outflow
or
trabeculectomy
Closed-angle ("acute") Glaucoma
emergency-can cause permanent damage or blindness
when the able between the cornea and iris closes suddenly
blocks trabecular meshwork
eye pressure increases rapidly from aqueous humor build up
extremely red and painful eye, very hard, nausea, vomiting
Treatment for closed-angle glaucoma
laser-burned hole through the iris (laser iridotomy)
The Lens
biconvex, transparent, flexible
avascular and no innervation
2 regions of the lens
the lens epithelium
the lens fibers
The lens fibers take up...
most of the lens
Presbiopia is managed with...
bifocals
A cataract happens when...
the lens is milky and opaque
clumping of crystal proteins
Visible Light Spectrum is...
400 to 700 nm
Path of Light
light source--cornea--aqueous humor--lens--vitreous humor--neural
layer of retina--photoreceptors with bipolar and ganglion cells--optic
nerve--optic chiasma--optic tract--lateral geniculate nucleus of the
thalamus--optic radiation--primary visual cortex in occipital lobe
What happens to light in the eye?
It gets refracted.
Focal Point
the place where light rays converge at a single point
What places in the eye have constant refraction?
the cornea, aqueous humor, vitreous humor
Variable Refraction is accomplished via...
the lens
Sympathetic activation on the lens uses...
distant vision
ciliary body and zonules pull and flatten lens
pupil dilates to increase light entering the eye
Parasympathetic activation on the lens uses...
close vision
ciliary body contracts resulting in ciliary zone relaxation and
lens balls back up
pupil constricts to decrease light entering the eye
Emmetropic means...
normal.
99% of refractive problems are related to
eyeball shape.
Presbyopia means
Old Person's Vision
For close focus, 3 things must occur...
accommodation of the lens
constriction of the pupils
convergence of the eyeballs
Accommodation of the lens (for close vision) requires...
CN III (Oculomotor Nerve)
*None of this happens after age 50
Constriction of the Pupils (for close vision) requires...
parasympathetic activation.
called accommodation pupillary reflex
Convergence of the Eyeballs (for close vision) requires...
CN III activation, with the medial, superior, and inferior rectus
muscles that bring the eyes inward
Phototransduction is....
the process by which light energy is converted into a graded receptor
potential (chemical energy)
Rods and Cones are embedded where?
in the pigmented layer of the retina
Rod Cells contain the visual pigment...
Rhodopsin.
Rod Cells are best suited for...
night vision.
(only picks up shades of gray or purple)
Cone Cells have one of 3 different types of photo pigments..
blue cones
green cones
red cones
(for color vision)
For low-intensity light...
little rhodopsin is bleached and the retina continues to respond to
light stimuli.
For high-intensity light...
great amounts of rhodopsin is bleached, and bleached again after it
is reformed
-The rods then become non-functional, but the cones still work
Dark adaptation takes how long?
20 minutes
Light adaptation takes how long?
5 to 10 minutes
Night blindness or Nyctalopia means...
rod cell function is very poor.
2 common causes of night blindness
prolonged vitamin A deficiency
retinitis pigmentosa
Retinitis Pigmentosa is...
a disease where the pigmented layer of the retina is poor at
recycling damaged rod cells.
Colorblindness is...
a congenital lack of one or more cone types
X-linked (more common in males)
Red and Green colorblindness is...
the most common type of color blindness.