Download Anatomy of the Eye, Conditions, and Functional Implications

Session 2: Wednesday, September 16, 2015:
Anatomy of the Eye, Associated Eye
Conditions and Functional Implications
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Housekeeping items
Start Anatomy of Eye, Associated Conditions
and Functional Implications
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Any questions from last week?
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Textbook
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Weekly discussion
◦ Any questions?
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Protect the eye from injury
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Exclude excessive light from the eyes
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Cleanse and moisten the cornea
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We have an upper and lower eyelid
◦ The only difference between the two is the presence
of the levator palpebral superious muscle in the
upper lid
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When we discuss the size of an eyeball, we
are referring to the size of the palpebral
fissure
◦ Normal is 30mm wide, 15mm high
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The lid margin is separated into anterior and
posterior portions by the “gray line”
Eyelashes are on the anterior portion of this
line
◦ They also protect the eye and are innervated by
sensory nerves
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Modified oil and sweat glands open into the
follicles of the lashes
◦ Some of these glands secrete the oily layer of the
tear film
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The lids are composed of 7 layers
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There are three types of lid abnormalities
◦ Ptosis
◦ Ectropion
◦ Entropion
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Moistens
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Cleans
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Lubricates
◦ Prevents friction between the eye and the lids
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The lacrimal gland contributes secretions to
the tear film
Tear film has 3 layers
◦ Lipid (fat) layer – from glands connected to lashes
◦ Aqueous layer – from lacrimal gland
◦ Mucous layer – from cells in conjunctiva
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Blinking maintains a continuous tear film
layer over the surface of the eye
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Tears drain into the
lacrimal sac and
nasolacrimal duct via
the lacrimal puncta
Tears drain out of the
eye with blinking
Some infants can have
an obstrucion in the
nasolacrimal duct
The nasolacrimal duct
drains into the nose
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The eyes reside in 2 symmetrical bony cavities
called the orbits
Serve to protect and maximize the function of
the eye
Is pear-shaped with the widest diameter at the
front
7 bones contribute to form the orbital walls
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Frontal
Lacrimal
Palentine
Zygomatic
Maxilla
Sphenoid
Ethmoid
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The orbit contains:
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Eyeball in the anterior portion (1/5 of the space)
Optic nerve
The 6 extraocular muscles
Nerves which innervate/stimulate the muscles
Blood vessels
Lacrimal gland
Connective tissue
Fat
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They function to move the eye in different
directions
◦ Provide us with binocularity
◦ Provide us with an expanded visual field
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They move and rotate the eye in all directions
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There are 6 in each orbit
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Lateral Rectus
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Medial Rectus
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Superior Rectus
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Inferior Rectus
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Superior Oblique
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Inferior Oblique
◦ Moves the eye horizontally (out)
◦ Innervated by the 6th CN
◦ Moves the eye horizontally (in)
◦ Innervated by the 3rd CN
◦ Move eye up (also in and intorts)
◦ Innervated by the 3rd CN
◦ Moves the eye down (also in and extorts)
◦ Innervated by the 3rd CN
◦ Intorts the eye (also moves down and out)
◦ Extorts the eye (also moves up and out)
◦ Innervated by the 3rd CN
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When there is a problem with the extraocular
muscles (length, placement or ability to
function) the eyes will not be properly
aligned, and the images seen by the two eyes
are too dissimilar for the brain to fuse them
This will result in either the brain suppressing
one eye, or double vision
Misaligned eyes = Strabismus
Brain suppression = Amblyopia
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Amblyopia will be discussed in a later slide
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Strabismus can be:
◦ Tropic – cannot be controlled under binocular
viewing conditions
◦ Phoric – can be controlled by the brains efforts to
achieve binocular vision
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Strabismus occur for many reasons
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Inherited (common)
Paresis
Trauma
Restriction
As the result of another syndrome/disorder
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Esotropia
◦ An inward turning of the eyes
◦ Most common form of strabismus
◦ Congenital esotropia can appear in the first 6
months of life
◦ Usually impaired depth perception
◦ Can be treated with eye muscle surgery
◦ Accommodative esotropia can be treated with
glasses for near
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Exotropia
◦ An outward turning of the eyes
◦ Common strabismus of childhood
◦ Usually starts of intermittent, and can sometimes
stay that way
◦ Can be worse for distance fixation and in bright
light
◦ If it becomes constant, eye muscle surgery can help
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There are other conditions that can cause
strabismus
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Thyroid Eye Disease
Superior Oblique Palsy
Brown’s Syndrome
Duane’s Syndrome
Orbital Floor Fracture
Strabismus in children will lead to
suppression and amblyopia
Strabismus in adults will lead to diplopia
(double vision)
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A thin, translucent, mucous membrane that
helps protect the eyeball
It covers the undersurface of the lid, the
curves and covers the sclera (white part of the
eye) and ends at the cornea
A transparent barrier covering the contents of
the orbit
Conjunctivitis (pinkeye) is an inflammation or
infection of the conjunctiva
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Fibrous layer that provides support to the
globe
Helps to maintain the shape of the eye
The extraocular muscles attach to the sclera
to move the eye
It covers the entire globe except for the front
of the eye (cornea)
The boarder between the cornea and the
sclera is called the corneoscleral limbus
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Is the major refractive surface of the eye (2/3
of eye’s refracting power)
Is the window for the eye, therefore any
disease or injury can adversely affect vision
Corneal transparency is due to:
◦ The arrangement of cells
◦ The avascularity
◦ The regularity and smoothness of the epithelium
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The cornea is composed of 5 layers:
◦ Epithelium
 Must be kept moist to maintain transparency and
nutritional status
 Responds rapicly to repair
◦ Bownman’s layer
 Cannot regenerate if damaged – will scar
◦ Stroma
 Makes up 90% of the corneal thickness
 If penetrated is vulnerable to infection and scarring
◦ Descemet’s Membrane
◦ Endothelium
 Contains a pump which dehydrates and nourishes the
cornea
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Refracting power
◦ Light rays enter the eye through the cornea and are
bent so that they converge at a point of focus on
the retina (macula)
◦ Sometimes light rays are not focused on the retina
due to
 The size of the eyeball
 The shape of the eyeball
 The curvature of the cornea
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Hyperopic (farsighted)
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Light rays converge behind the retina
The eyeball is too short
Will need glasses for near
Example Rx: +4.00
Plus lens
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Myopic (nearsighted)
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Light rays converge in front of the retina
The eyeball is too long
Will need glasses for distance
Example Rx: -5.75
Minus lens
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Astigmatic
◦ Light rays converge on more than one axis
◦ The eyeball is shaped more like a football with a
short axis and a long axis
◦ Will be corrected with glasses with a cylindrical lens
◦ Example Rx: +2.50-1.75x180
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Refractive Errors
◦ Occur in 52% of the population over three years of
age
◦ Can be corrected with
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Eye glasses
Contact lenses
Intraocular lens implants
Refractive surgery (in some cases)
◦ In patients with significant myopia, the length of
the eye can continue to increase, causing it to
become thin and stretched.
 Can cause the lens of the eye to dislocate
 Can put the patient at risk for retinal detachments
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Amblyopia
◦ In children, before the age of about 10, uncorrected
refractive errors can cause amblyopia
◦ Is defined as the reduction of visual acuity in one or
both eyes due to poor visual input
 Without this input, the brain fails to develop properly
◦ Most common cause of monocular vision loss
◦ Can be caused by
 Strabismus
 Refractive errors
 Deprivation
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If caused by strabismus
◦ The misaligned eye is suppressed (ignored) to prevent
double vision
◦ Sometimes strabismus surgery will re-align the eyes and
make the brain pay attention to the eyes once again
◦ Patching is required!
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If caused by refractive errors
◦ Unequal refractive errors (anisometropia)
◦ The brain will only pay attention to the eye with the clear
vision
◦ Glasses will help to level the playing field
◦ Patching is required!
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If caused by deprivation
◦ The brain will only pay attention to the clear image
◦ Surgery to remove a cataract, etc. is necessary
◦ Patching is required!
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Amblyopia Treatment
◦ This is required in most cases of amblyopia
◦ The better seeing eye is either patched or blurred to
force the eye to pay attention to the weaker eye
 Can wear an eye patch
 Can use Atropine drops
◦ Vision in both eyes must be monitored closely in both
eyes
◦ The visual system can respond to amblyopia treatment
until about 8-10 years of age
◦ The younger the child, the better the chances of
recovering vision
◦ If amblyopia is detected late, or treatment is
unsuccessful, the vision loss is irreversible.
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While patching, students will be functioning
with a lowered visual acuity and temporary
accommodations may need to be made.
Depth perception
Compliance with patching can be an issue.
Parents, teachers and students will need
support.
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Keratoconus
◦ An extreme form of corneal curvature, whereby the
cornea becomes cone shaped
◦ The center of the cornea becomes thin and in
extreme cases can rupture
◦ Is rare
◦ Bilateral
◦ Inherited
◦ More common in males
◦ Presents as blurry vision in the teenage years
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Can be associated with other conditions and
diseases
◦ Down Syndrome
◦ RP
◦ Aniridia
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Contact lenses are helpful in the early stages
◦ Usually rigid lenses
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Corneal transplant may be necessary in later
stages
◦ Is successful in over 85% of cases
Blurred vision –
 Large print, electronic text or magnification
 Assistive technology i.e. Zoomtext or
Quicklook
 Monocular
 Receiving notes from the board or electronic
notes i.e. through email or a memory stick
Sensitivity to light
• wearing brimmed hats or sunglasses
• Sitting with their back to windows
• Closing blind or curtains.
• When possible dimming lights or using a
• Desk light.
Poor Night Vision
• May require assistance at night or the use of a white cane.
Eye Strain or fatigue –
• Use large and high contrast print
• Take frequent breaks from using visual materials
• Use auditory materials for longer reading assignments
Next week we move inside the eye….stay tuned!