Exam 7 - Second Set (Eye slide 14 - Image slide 50) Flashcards
Six extrinsic muscles move each eye:
Superior rectus Inferior rectus Lateral rectus Medial rectus Superior oblique Inferior oblique
The extrinsic muscles of the eye are innervated by some combination of cranial nerves
III, IV, or VI
The ___ eye muscles move the eyeball laterally, medially, superiorly, and inferiorly
extrinsic
___ muscles move the eye in a plane (for the most part, anyway—the superior and inferior rectus are not on the exact midline)
Rectus
The ____ muscles preserve rotational stability of the eyeball
oblique
There are eight cardinal directions of eye movement. What are they?
superior, inferior, nasal, temporal, up & in, up & out, down & in, and down & out, shown here for the right eye
slide 17
Six of the eight cardinal directions of eye movement are associated with a single extrinsic muscle. These six are termed ____. Only the two remaining directions of eye movement (ie. the non-cardinal directions) are caused by two muscles acting in concert.
cardinal directions of gaze
The six directions that involve a single muscle are circled (the cardinal directions of gaze), along with the muscle that moves the eye in that direction from the starting point of looking straight ahead. (Right eye illustrated)
Slide 19
Cranial nerve __ is associated with multiple directions
III
Slide 20
The following “formula” may be useful…
for eye muscle innervation
LR6 (SO4) 3
LR6 = lateral rectus is innervated by?
SO4 = superior oblique is innervated by?
Subscript 3 = all other muscles are innervated by?
cranial nerve 6 (CN VI)
cranial nerve 4 (CN IV)
cranial nerve 3 (CN III)
Smoothly and uniformly moving the eye from the starting position of looking straight ahead to the final position of one of the cardinal directions of gaze is not an easy achievement. In practice, moving the eye generally involves more than one extrinsic muscle, and therefore frequently, more than one nerve. These combined actions need to be negated in order to properly assess the function of individual muscles and nerves.
Ok cool
In order to eliminate the effects of combined action on the eye by two extrinsic muscles, and their associated cranial nerves, the action of muscles (and associated nerves) must be isolated.
Alright we get it
When the eye is fully abducted (away from the nose), only the ____ muscles can elevate and depress the eye, respectively.
superior and inferior rectus.
This is purely a mechanical property caused by the axis of the eye lining up perpendicular to the superior/inferior rectus muscles.
When the eye is fully adducted (toward the nose), only the superior and inferior oblique muscles can ____.
depress and elevate the eye.
In this case, the superior oblique depresses the eye, and the inferior oblique elevates the eye
In this course whenever you see an “H” superimposed over the eye, the situation refers to a patient exam.
The directional arrows may still be retained in illustrations that have the “H”
Slide 24
During a patient exam, these isolating effects are applied by having the patient fully ___ the eye then look up and down. Next, fully adduct the eye and look up and down. This results in an “H” shaped pattern of eye movement. The six directions encompass the cardinal directions of gaze.
abduct
Eliminating combined action… But there is a slight complication resulting from this isolation mechanism. Recall that starting from the position of looking straight ahead, the inferior oblique is responsible for moving the eye up and out. Eye placement is then in the “up & out” quadrant due to action of the ____ (innervated by cranial nerve III).
inferior oblique
Eliminating combined action… But during a patient exam when the eye is fully abducted (by the lateral rectus), the mechanics of the situation are such that the ____ now elevates the eye. Eye placement is then in the “up & out” quadrant due to action of the superior rectus (still innervated by cranial nerve III).
superior rectus
Eliminating combined action… Starting with the eye looking straight ahead, the ___ is responsible for moving the eye down and out. At the end of the action, the eye is in the “down & out” quadrant due to action of the ____
superior oblique
(innervated by CN IV).
Eliminating combined action…
With the eye fully abducted (the bar of the “H”) during an exam, the ____ depresses the eye. At the end of this action, the eye is in the “down & out” quadrant due to action of the ___
inferior rectus (innervated by CN III).
Eliminating combined action… None of this changes the formula ___, which relates to the cranial nerves that supply particular extrinsic eye muscles. That relationship does not change
LR6 (SO4) 3
Eliminating combined action… What does change in some instances is the muscle that achieves the final result of moving the eye up or down when comparing the cardinal directions of gaze versus the cardinal directions of eye movement. And since that muscle may have changed, the ___ associated with that resultant action may also have changed.
nerve
Brace yourself and look at slide 28
What’s even going on there?
Much of the time, the concern is not so much with the muscles involved in moving the eye, but rather with the ___ involved. For that reason, we will spend some time on the __.
nerves
The cranial nerve associated with each of the cardinal directions of gaze is shown for the right eye. Cardinal directions of gaze ___ actions of individual extrinsic muscles of the eye, and their cranial nerves, enabling a determination of damage to the muscle or cranial nerve.
isolate
slide 30, 31
Although CN III (oculomotor) innervates the inferior rectus which causes movement in this direction from the starting point of looking straight ahead, with the eye fully adducted the only muscle that can depress the eye is the
superior oblique, which is innervated by CN IV (trochlear)
Although CN IV (trochlear) innervates the superior oblique which causes movement in this direction from the starting point of looking straight ahead, with the eye fully ___ the only muscle that can depress the eye is the inferior rectus, which is innervated by CN III (oculomotor)
abducted
The details of why a given muscle exhibits the particular action it has, or why a certain eye movement is associated with a specified cranial nerve are frequently of no concern in a clinical setting, as illustrated by this extract from Bates
Slide 34
An imbalance in the extrinsic eye muscles resulting in the misalignment of one eye so that its line of vision is not parallel with that of the other eye (cross-eyes).
Strabismus
Both eyes are not pointed at the same object at the same time
Strabismus
In strabismus, to compensate, the normal and deviant eyes may alternate in focusing on objects. In other cases, only the controllable eye is used, and the brain begins to disregard inputs from the ___, which then becomes functionally blind
deviant eye
Can strabismus be outgrown?
No
Strabismus treatment?
Less severe cases may be treated with eye exercises to strengthen the weak muscles, or by temporarily placing a patch on the stronger eye thereby forcing the child to use the weaker eye
When the above do not correct the situation, surgery on the eye muscles is needed
Layman’s term for strabismus?
Lazy eye
rapid involuntary movement of the eyeballs
May be inherited, idiopathic, or caused by a disease of the central nervous system
Nystagmus
a sign, not a disease
There are a number of types of nystagmus, and a number of causes
occurs much less frequently than horizontal nystagmus
Vertical nystagmus
complex of eye movements that occurs during and immediately after rotational motion
Vestibular nystagmus
In police work, testing for ___ is one of a battery of field sobriety tests used by officers in the field to determine whether a suspect is driving under the influence of alcohol
horizontal gaze nystagmus
The eye consists
of three layers:
Fibrous tunic
Vascular tunic
Retina
Is the superficia coat of the eyeball
Is avascular
Fibrous tunic
Fibrous tunic consists of?
Cornea
Sclera
Transparent coat that covers the iris
Cornea
Is curved, so it focuses light
Cornea
The “white” of the eye
Sclera
Dense connective tissue, mostly collagen and fibroblasts
Sclera
Covers the entire eyeball except the cornea
Gives shape to eyeball, makes it more rigid, and protects inner parts of the eye
Sclera
The middle layer of the eye
Vascular tunic
Vascular tunic composed of?
Choroid
Ciliary body
Iris
Highly vascular
Lines most of the internal surface of the sclera
Choroid
Provides nutrients to the posterior surface of the sclera
Choroid
Ciliary body Consists of:
Ciliary processes
Ciliary muscle
Protrusions or folds on the internal surface of the ciliary body
Contains blood capillaries that secrete aqueous humor
Ciliary processes
A circular band of smooth muscle that alters the shape of the lens
When it contracts it reduces tension on suspensory ligaments that hold the lens, thereby allowing it to assume a more spherical shape (for closer vision)
Ciliary muscle
the colored portion of the eyeball
Iris
It is attached at its outer margin to the ciliary processes
Iris
Iris regulates the amount of light entering the eye through the pupil,
via autonomic reflexes
autonomic
____ neurons stimulate the sphincter pupillae (circular muscles) contract to cause a decrease in the size of the pupil (constriction)
Parasympathetic
Sympathetic neurons stimulate the dilator pupillae (radial muscles) of the iris to contract, causing an
increase in the size of the pupil (dilation)
The third, and inner coat of eyeball
Retina
The retina lines the ___ ¾ of the eyeball
posterior
It is the beginning of
the visual pathway
Retina
The surface of the retina is the only place in the body where ___ can be viewed directly (ophthalmoscope) and examined for pathological changes
blood vessels
is the site where the optic nerve exits the eyeball
optic disc
The ___ retinal artery and ___ retinal vein are adjacent to the optic disc
central
The pigmented layer of the retina is a sheet of ___ coated epithelial cells.
It absorbs stray light, thereby preventing reflection and scattering
melanin-
The neural layer of the retina is an outgrowth of the brain
It has three distinct layers of retinal neurons:
Photoreceptor layer
Bipolar layer
Ganglion layer
The neural layer of the retina also has two zones—a zone between each layer:
Outer synaptic layer
Inner synaptic layer
Two types of photoreceptors transduce light rays into receptor potentials:
Rods
Cones
have a low light threshold and enable seeing only shades of gray
Rods
have a higher light threshold and provide color vision
Cones
in the exact center of the visual axis of the eye of the posterior portion of the retina
macula lutea
a small depression in the center of the macula lutea
The central fovea
The ____ contains no rods or cones
An image that strikes the ___ can not be seen
optic disc
It is therefore called the blind spot
degenerative disorder of the retina and pigmented layer that may begin to show effects in persons 50 years of age and older
Abnormalities occur in the region of the macula lutea
Age-related macular disease
Also called macular degeneration
Victims of advanced AMD retain peripheral vision but lose the ability to see straight ahead
Age-related macular disease two forms?
“Dry” in which central vision gradually diminishes because the pigmented layer atrophies and degenerates. There is no effective treatment for this form.
“Wet” form in which new blood vessels form in the choroid and leak plasma or blood under the retina. Treatment for this form is laser surgery to destroy leaking blood vessels
behind the pupil and iris
lens
consists of proteins called crystallins, which are arranged like the layers of an onion, and enclosed in a capsule
lens
It is transparent (normally), and lacks blood vessels
It is the variably refractive medium of the eye
lens
Loss of transparency of the lens is termed a
cataract
The lens becomes cloudy due to changes in the structure of lens proteins
When cataracts occur they are generally associated with aging, but they may be due to injury, excessive exposure to UV light, some medications (long-term steroid use), disease (diabetes), chemicals (glutaraldehyde, osmium tetroxide), and an increased risk due to ___
risk due to smoking
Surgical removal of the affected lens and implantation of a new artificial lens usually restores sight
The lens divides the eye into two cavities:
Anterior cavity
Vitreous chamber
The anterior cavity consists of two chambers:
Anterior chamber, between the cornea and iris
Posterior chamber, behind the iris, and in front of the lens
Both chambers are filled with aqueous humor
Anterior chamber, between the cornea and iris
Posterior chamber, behind the iris, and in front of the lens
Major contributor of intraocular pressure
Manufactured by filtration of blood by capillaries of the ciliary processes
Aqueous humor
Aqueous humor Flows between the iris and the lens, through the pupil, into the anterior chamber
From the anterior chamber it drains into the ____, which is at the junction of the sclera and cornea.
Then returns to the blood.
scleral venous sinus (canal of Schlemm)
Normally replaced about every 90 minutes
high intraocular pressure
When unchecked, ____ damages the optic nerve and retina, resulting in blindness
glaucoma
Glaucoma is usually caused by impaired drainage of aqueous humor
The canal of Schlemm is at the vertex of the angle formed by the intersection of the cornea and the iris, called the
ocular angle
In primary closed angle glaucoma, pressure from the ____ chamber pushes the iris forward, closing the ocular angle and preventing drainage of aqueous humor
posterior
In primary open angle glaucoma the ocular angle remains open, but abnormalities in the trabecular meshwork associated with ___ impede the outflow of aqueous humor
Schlemm’s canal
Glaucoma is treated with cholinergic agonists (cholinomimetics), which constrict the pupil, ___ the ciliary muscles, and decrease intraocular pressure
contract
In ___ angle glaucoma, pupillary constriction lowers intraocular pressure by pulling the iris away from the canal of Schlemm and opening the angle
In ___ angle glaucoma, contraction of the ciliary muscle stretches the trabecular meshwork thereby opening its tubules
closed
open
The larger of the two cavities
Vitreous chamber
Jellylike substance
Contributes to intraocular pressure
Holds retina flush against the choroid
vitreous body of vitreous chamber
Contains phagocytic cells that remove debris, thereby providing for unobstructed vision
Formed during embryonic development, and not replaced thereafter
vitreous body of vitreous chamber
Hyaloid canal is the remnant of the ___ artery
hyaloid
vitreous body of vitreous chamber composed mostly of?
Water
Hyaluronic acid
Collagen
Vitreous body: Attachments to the retina, which are important in understanding retinal tears and retinal detachment, are
Just behind the ora serrata
At the optic disk
the serrated junction between the retina and the ciliary body.
ora serrata
This junction marks the transition from the simple non-photosensitive area of the retina to the complex, multi-layered photosensitive region.
ora serrata
The ___ attaches anteriorly just behind the ora serrata.
vitreous body
Loss of transparency of the lens due to changes in the structure of lens proteins typically due to aging, injury, excessive exposure to UV light, chemicals, or medications?
Abnormally high intraocular pressure due to buildup of aqueous humor within the anterior cavity?
Cataract.
Glaucoma
inflammation of the eyelid?
Inflammation of the conjunctiva due to bacteria (contagious) or irritants (not contagious) ?
Blepharitis
Conjunctivitis (pinkeye).
A scratch on the surface of the cornea?
Procedure in which a donor cornea replaces a removed defective cornea?
Corneal abrasion.
Corneal transplant.
Degenerative disease of the retina due to diabetes mellitus, in which blood vessels in the retina are damaged or new ones grow and interfere with vision?
Turning outward of the eyes ?
An inflammation or infection of the cornea?
Diabetic retinopathy.
Exotropia.
Keratitis.
Constriction of the pupil ?
Dilation of the pupil?
Abnormal visual intolerance to light ?
Miosis.
Mydriasis.
Photophobia.
Falling or drooping of the eyelid (or slippage of any organ below its normal position) ?
A tumor arising from immature retinal cells; accounts for 2% of childhood cancers?
Ptosis.
Retinoblastoma.
An area of reduced or lost vision in the visual field?
Instrument for measuring intraocular pressure?
Scotoma.
Tonometer.
A serious form of conjunctivitis, and the greatest single cause of blindness in the world, caused by the bacterium Chlamydia trachomatis; produces an excessive growth of subconjunctival tissue and invasion of blood vessels into the cornea, progressing until the entire cornea is opaque
Trachoma.
