Fundamentals of Ophthalmology Flashcards
What is the volume of the adult orbit?
Slightly less than 30cc or one ounce
(about the size of a shot glass)
What are the average
dimensions of the orbital entrance?
35 mm in height by 45 mm in width
Where does the maximum
width of the bony orbit occur?
1 cm behind the anterior orbital margin
What is the depth
range of the adult orbit?
4.0-4.5 cm
Name the seven bones that make up the orbit?
Bones of the Orbit:
- Maxillary
- Frontal
- Zygomatic
- Ethmoid
- Lacrimal
- Sphenoid
- Palatine
Mnemonic:
Many Friendly Zebras Enjoy Lazy Summer Picnics
What two bones form the orbital roof?
Frontal (orbital plate) and
lesser wing of spenoid
Mnemonic: Front-less
“2-2-3-4, all have sphenoid except the floor” - order is roof, lateral, floor, medial
What two bones form
the lateral orbital wall?
Greater Wing of sphenoid and zygoma
Mnemonic: Great-Z
“2-2-3-4, all have sphenoid except the floor” - order is roof, lateral, floor, medial
What three bones form
the orbital floor?
Palatine, maxilla, and
zygoma (orbital plate)
Mnemonic: PaM-Z
“2-2-3-4, all have sphenoid except the floor” - order is roof, lateral, floor, medial
What four bones form
the medial orbital wall?
Ethmoid (orbital plate), lacrimal, maxilla (frontal process), and lesser wing of sphenoid
Mnemonic: ELMS
“2-2-3-4, all have sphenoid except the floor” - order is roof, lateral, floor, medial
What bone forms the
anterior lacrimal crest?
Lacrimal
What bone forms the
posterior lacrimal crest?
Maxilla
What structure lies 4 mm behind the superior orbital margin medially and of what is it composed?
Trochlea- Hyaline cartilage
Which bone makes up
the largest portion of the medial wall?
Ethmoid
What is another term for the
ethmoid bone in the medical wall?
Lamina papyracea- “paper-thin layer”
The nasolacrimal canal
extends into what part of the nose?
Inferior meatus
What muscle arises from the orbital
floor just lateral to the opening of the
nasolacrimal canal?
Inferior oblique
Name six clinical features
of a blowout fracture?
Clinical Features of a Blowout Fracture:
- Diplopia
- Enophthalmos
- Hypesthesia of the infraorbital nerve
- Positive forced ductions
- Fluid level in maxillary sinus
- Periorbital crepitus
Which wall of the orbit is the
thickest and strongest?
Lateral Wall
What four structures
attach to the lateral orbital tubercle?
- Check ligament of the lateral rectus
- Suspensory ligament of the eyeball (Lockwood’s Ligament)
- Lateral palperbral ligament
- Levator aponeurosis
What structures
pass through the optic foramen?
- Central retinal vein
- Optic nerve
- Ophthalmic artery
- Sympathetic fibers from the carotid plexus
What bone does
the optic foramen pass through?
Lesser Wing of the Sphenoid
What travels through
the supraorbital foramen?
Blood vessels and the Supraorbital nerve (Branch of V<sub>1</sub>)
What travels through
the zygomatic foramen?
Zygomaticofacial and Zygomaticotemporal branches of
Zygomatic Artery and Nerve
The infraobital nerve is a
branch of which division of CN V?
V2 - Maxillary
What passes through the
superior part of the
superior orbital fissure?
- Lacrimal branch of CN V
- Frontal branch of CN V
- CN IV (Trochlear nerve)
Mnemonic: LFT
Superior part- above origin site of the lateral rectus
What divides the inferior and
superior parts of the
superior orbital fissure?
Origin of the lateral rectus muscle
What seven structures passes through
the inferior division of the
superior orbital fissure?
- Superior division of CN III
- Inferior division of CN III
- Nasociliary branch of CN V
- CN VI (Abducens nerve)
- Superior ophthalmic vein
- Inferior ophthalmic vein (part that drains into cavernous sinus with superior ophthalmic vein)
- Sympathetic nerve plexus
Inferior part- below origin site of the lateral rectus
What four structures
passes through the
inferior orbital fissure?
- Maxillary part of CN V
- Pterygoid part of CN V
- Nerve from the pterygopalitine ganglion
- Inferior Ophthalmic vein (the part that drains into ptyregoid venous plexus)
Where do the axons
of the optic nerve originate?
Ganglion cell layer of the retina
How many axons
comprise the optic nerve?
1 - 1.2 million
What is the length of the optic nerve?
3.5 - 5.5 cm, averages 4.0 cm
Name the four parts of the optic nerve and their respective lengths?
Intraocular- 1 mm
Intraorbital- 2.5 cm
Intracanalicular 4 - 10 mm
Intracranial 1.0 cm
What are the dimensions
of the optic nerve head?
1.75 mm vertically by 1.5 mm horizontally
After passing posterior to what anatomic landmark does optic nerve axons become myelinated?
Lamina cribosa
What type of cells
surround the optic nerve?
Glial cells
The optic nerve is developmentally part of the brain.
What arises from the Annulus of Zinn?
The rectus muscles
Which muscles originate partially from the sheath of the optic nerve and why is this clinically important?
Superior rectus and medial rectus.
Patients with retrobulbar neuritis
will complain of pain with EOM.
Why is it clinically important that the dural sheath of the optic nerve is fused to the periosteium in the canal?
Blunt tramua, especially to the brow, may be transmitted to the optic canal and cause a shearing of the dura and periosteum, compromising blood flow and causing ischemia of the optic nerve.
What is the blood supply of the surface
of the optic nerve head?
Central retinal artery or
small cilioretinal arteries
What is the blood supply
of the prelaminar region
and the lamina cribrosa?
Branches of the posterior ciliary arteries
Discuss the watershed zone formed by
the terminal posterior ciliary arteries.
When perfusion pressure drops, the area of the optic nerve contained within the watershed zone is prone to ischemic damage - e.g. anterior ischemic optic neuropathy
What is the blood supply
to the intraorbital part of the optic nerve?
Intraneural branches of the central retinal artery and pial branches from the peripapillary choroid, the central retinal artery and ophthalmic artery
What is the blood supply of the
intracanalicular part of the optic nerve?
Ophthalmic artery
What is the blood supply of the
intracranial part of the optic nerve?
Branches of the internal carotid
and ophthalmic arteries
The superior division of
CN III innervates what two muscles?
- Superior rectus
- Levator palpebrae superioris
The inferior division
of CN III innervates what three muscles?
- Medial rectus
- Inferior rectus
- Inferior oblique
What is carried on CN III, from where does it arise, and what does it innervate?
Parasympathetics that arise from the ciliary ganglion innervate the pupillary sphincter and ciliary body
How does a complete paralysis
of CN III present?
Ptosis (levator), inability to move
the eye up or in (eye looks
down and out), mydriasis
(pupillary sphincter)
What is unique about the location of the cell bodies of the part of CN III that innervates the levator?
They are found in
a single midline nucleus
What CN has the longest
intracranial course and how long is it?
CN IV- Trochlear
7.5 cm
Which superior oblique
does the right trochlear nucleus control?
Left superior oblique
The motor portion of CN V innervates what structues?
Muscles of mastication
Name the three sensory division of CN V and the
subdivision of CN V1?
V1 - ophthalmic (lacrimal, frontal, and nasociliary)
V2 - maxillary
V3 - mandibular
Other than the lateral rectus muscle,
what does CN VI (abducens) innervate?
Nothing
Where is the ciliary ganglion located?
Within the muscle cone,
1 cm in front of the annulus of Zinn, between the optic nerve and the lateral rectus muscle.
What are the three roots of the ciliary ganglion?
- Long (sensory) root
- Short (motor) root
- Sympathetic root
Discuss the long (sensory) root of the ciliary ganglion?
Arises from the nasociliary branch
of CN V and contains sensory fibers
from the cornea, iris, and ciliary body.
Discuss the short (motor) root
of the ciliary ganglion?
Arises from the inferior division of CN III, synapses in the ganglion, and carries parasympathetics to the iris sphincter and ciliary muscle.
Discuss the sympathetic root
of the ciliary ganglion?
Arises from the plexus around the internal carotid artery and innervates blood vessels of the eye and dilator fibers of the iris.
What three ganglions are represented
in the short ciliary nerve?
- Ciliary
- Superior cervical
- Trigeminal ganglion
What muscle does not originate
from the obital apex and
from which bone does it originate?
The inferior oblique originates from
the orbital plate of the maxilla.
What is the Spiral of Tillaux?
It is the shape formed by the
insertions of the rectus muscles -
5.5, 6.5, 6.9, 7.7 mm from the limbus
(medial, inferior, lateral, superior).
What is the blood supply
of the lateral rectus muscle?
Why is it unique?
A single branch of the lacrimal artery
supplies the lateral rectus making it the only extraocular muscle supplied by only one vessel.
Which two muscles receive
blood supply from the infraorbital artery?
- Inferior oblique
- Inferior rectus
What are the names of the two groups
of fibers that make up the eye muscles and what are their differences?
Fibrillenstruktur- fast or twitch movements, individual neuromuscular junctions, no acetylcholine receptors
Felderstruktur- slow or tonic movement, multiple neuromuscular junctions, have acetylcholine receptors
What are the dimensions
of the normal adult palpebral fissure?
2.7 - 3.0 cm in width
by 0.8 -1.1 cm in height
How far can a normal
levator muscle raise the upper eyelid?
1.5 cm
How much elevation can the frontalis muscle add to levator function?
2 mm
Name the muscle responsible
and the clinical feature of the palebral
fissure change that occurs
in hyperthyroidism?
Muller’s muscle- retraction
Name the muscle responsible
and the clinical feature
of the palebral fissure change
that occurs in Horner Syndrome?
Muller’s muscle- ptosis
Name the muscle responsible and
the clinical feature of the
palebral fissure change that occurs
in facial palsy (e.g. Bell’s Palsy)?
Orbicularis oculi- lagophthalmos
Name the muscle responsible
and the clinical feature of the
palebral fissure change that
occurs in Third nerve palsy?
Levator- ptosis
What is the antagonist muscle of the levator?
Orbicularis oculi
What is special about
the skin of the eyelid?
It is the thinnest in the body
and has no subcutaneous fat.
Where does the levator aponeurosis
form its firmest attachments?
On the anterior surface
of the superior tarsus,
3mm superior to the lid margin
What is the name for the most
superficial portion of the orbicularis oculi?
Gray line-
a.k.a. the muscle of Riolan
Where are the eyelashes and
meibomian gland orifices found on the
lid margin in relation to the gray line?
Eyelashes arise anterior to the gray line
Meibomian gland orifices open posterior
Name the respective
secretion and location of
the Glands of Moll?
Aprocrine glands found
in the lid
Name the respective
secretion and location of
the Lacrimal Glands?
Eccrine glands located in the
superior lateral orbit and lid
Name the respective
secretion and location of
the glands of Krause and Wolfring?
Eccrine glands glands located in
the plica, caruncle, and lid
Name the respective
secretion and location of
the Meibomian Glands?
Holocrine glands located in the
tarus
Name the respective
secretion and location of
the Glands of Zeis?
Holocrine glands located in the
hair follicles, caruncle, and lids
Name the respective
secretion and location of
the Goblet Cells?
Holocrine glands located in the
conjunctiva, plica, and caruncle
Describe the anatomic
and functional components of the
orbicularis oculi muscle?
Orbital- voluntary closure
Palpebral (preseptal & pretarsal)-
voluntary & involuntary (blinking)
What is the orbital septum
an extension of?
Periosteum of the
roof and floor of the orbit
What is found just posterior
to the orbital septum?
Orbital fat
What is an important clinically distinction
found in orbital, but not
preseptal cellulitis?
Pain with EOM
What happens to the
levator muscle when it reaches
Whitnall’s ligament?
It turns from a horizontal to a
vertical direction and divides
anteriorly into the levator aponeurosis
and posteriorly into Muller’s muscle.
What forms Whitnall’s ligament?
A condensation of tissue
surrounding the superior rectus
and levator muscles
What is the tarsus composed of?
Dense connective tissue,
not cartilage.
What are the dimensions
of the upper and lower tarsal plates?
Upper- 29 x 1 x 11 mm
Lower- 29 x 1 x 4 mm
What is the name for misdirection
of the orientation of the eyelashes?
Trichiasis
What is the name for aberrant
growth of eyelashes through
the meibomian gland orifices?
Distichiasis
What type of muscle is
Muller’s muscle and
how is it innervated?
Smooth muscle that is
sympathetically innervated
What type of epithelium
covers the conjunctiva?
Nonkeratinized
squamous epithelium
What types of blood cells can
be found in the substantia propria
of the conjunctiva?
Lymphocytes, macrophages,
mast cells, and plasma cells
Where are goblet cells most
concentrated in the conjunctiva?
Inferior and medial conjunctiva,
plica semilunaris, and caruncle.
Where in the conjunctiva
can we find no goblet cells?
In the limbal region
What structure is fused with the
conjunctiva for ~2mm posterior to
the limbus?
Tenon’s capsule
What two main arteries supply
the eyelids?
External carotid
via the facial artery
Internal carotid via
branches of the ophthalmic artery
What are the two portions of the
venous drainage of the eyelids and
into what structures do they drain?
Pretarsal drains into the internal
and external jugular veins
Posttarsal drains into the cavernous sinus
Where are lymphatic found in the
orbit and to what nodes do they drain?
Conjunctiva paralleling vessels.
They drain into preauricular
and submandibular lymph nodes.
What is the name for the vestigial
structures in the eyelids that is
analogous to the nictitating
membrane of lower animals?
Plica semilunaris
What divides the lacrimal gland
into two parts?
The lateral expansion of the
levator aponeurosis.
Why do we biopsy the orbital portion
of the lacrimal gland when
biospy is needed?
To avoid sacrificing the excretory
ducts the pass through the
palpebral portion of the gland.
Where do the excretory ducts of
the lacrimal gland empty?
In the superior fornix
approximately 5 mm above the
superior border of the tarus.
When measuring basal tear secretion
(Schirmer’s test with anesthesia),
what glands are we testing?
Accessory lacrimal glands of
Krause and Wolfing
Remember the lacrimal gland
is responsible for reflex tearing,
and its contribution is removed
with the use of topical anesthetic.
In what percent of the population
do the two canliculi join to form
a common canaliculus?
90%- the other 10% have
two openings into their
lacrimal sac.
What percent of full term neonates
are born with a closed
nasolacrimal duct?
30%- most resolve spontaneously
with 6 months.
What structures penetrate
Tenon’s capsule?
- Optic nerve
- Posterior cililary nerves
- Posterior ciliary vessels
- Vortex vessels
The fusion of the sheaths
of the inferior rectus muscle,
the inferior tarsal muscle, and
the check ligaments of the
medial and lateral rectus muscles
form what structure?
The suspensory ligament
of the globe. Also known as
Lockwood’s ligament.
What is the range of normal
for AP diameter in the adult eye?
2.1-2.6 cm
What is the normal diameter
of the human eye at birth?
1.6 cm
When does the eye normally
reach its maximum size?
During puberty
What are the horizontal and vertical
measurements of the
adult cornea anteriorly?
Horizontal- 1.2 cm
Vertical- 1.1 cm
Where is the sclera the thinnest?
How thin is it?
Why is it clinically important?
At the insertions of the rectus muscles.
As thin as 0.3 mm. Care must be taken
to prevent inadvertent globe penetration
during the placement of bridle sutures
during strabismus surgery.
Where is the sclera the thickest?
How thick is it?
The sclera is 1 mm thick
at the posterior pole.
Where does the
inferior oblique muscle insert?
The medial border inserts at the
fovea and the lateral border
inserts more anteriorly.
Describe the position of
insertion of the superior oblique?
Posterior to the equator and
temporal to the vertical meridian.
What is the function of the
vortex veins? How many vortex
veins are there in each eye?
The vortex vein drain the choriod,
ciliary body, and the iris.
There are 4-7 per eye.
How far are the ampullae
of the vortex veins from the ora?
What does the circle of veins represent?
They lie 8-9 mm posterior to the ora.
The circle of ampullae forms the
equator of the fundus.
How many short posterior ciliary
arteries are found in each eye?
~20 per eye
How many short posterior ciliary
nerves are found per eye?
~10 per eye
How many long ciliary arteries
are found in each eye?
4 per eye
How many long ciliary nerves
are found in each eye?
4 per eye
From where do the
ciliary arteries arise?
Ophthalmic arteries
What are the three layers
of the tear film? What structures
make each of them?
Superfical oil layer created by
the Glands’ of Zeis, Glands’ of Moll,
and meibomian glands.
Middle aqueous layer created by
the Glands of Krause & Wolfring
Deep mucous layer created by
the goblets cells
What is the main refractive part
of the eye? What is its strength?
The cornea, tear film, and
aqueous form a lens with a
power of ~43 diopters in air.
This represent 2/3 of the eye’s
refractive power.
What is the central thickness
of an average cornea?
Peripheral thickness?
Central- 0.52mm
Peripheral- 1.0mm
Where is the cornea
normally steepest?
Centrally
From what embryonic tissue
is the corneal epithelium derived?
Surface ectoderm
What connects the basal cell layer
of the corneal epithelium
to its basement membrane?
Hemidesmosomes
What makes the corneal surface
naturally irregular and what
corrects for this irregularity?
Microplicae and microvilli give
the corneal surface a natural
irregularity which is corrected
by the precorneal tear film.
Where are the corneal epithelial
stem cells located?
At the limbus.
How thick is Bowman’s layer
and why is it called a layer
and not a membrane?
Bowman’s layer is 8-14 microns thick.
It is acellular and composed of
random collagen fibrils.
What happens to Bowman’s
layer after injury?
A scar forms because
Bowman’s layer is not replaced.
What composes 90% of the
corneal thickness? What
is it made up of?
The corneal stroma accounts
for 90% of the corneal thickness.
It is composed of fibroblasts
(keratocytes), ground substance,
and collagen lamellae
What is the macroperiodicity
of corneal collagen fibrils?
640 angstroms
What is corneal ground
substance composed of
and what synthesizes it?
Mucoprotein and glycoprotein.
It is synthesized by keratocytes.
What is the basement membrane
of the corneal endothelium called?
What special stain is used to
identify it?
Descement’s membrane.
It is PAS positive.
Describe the creation of the two
zones of Descement’s membrane?
The anterior banded zone
is created in utero.
The posterior nonbanded zone
is laid down by the corneal
endothelium throughout life.
What is the name for
peripheral excrescences
of Descemet’s membrane?
What about central ones?
Peripheral excrescences
are Hassall-Henle warts (common)
Central excrescences are guttata.
From which embryonic tissue
is the corneal endothelium derived?
Neural crest
How many cell layers make
up the corneal endothelium?
One
What do adjacent epithelial cells
share that endothelial cells lack?
Desmosomes
What happens to the corneal
endothelial cells with age?
Their numbers decrease and
they lose mitochondria. Remaining
cells spread in attempt to fill in any
gaps as corneal endothelial cells
normally do not ungergo mitosis.
Where do traumatic scleral
ruptures most frequently occur?
They occur most commonly
at the supranasal limbus, but
also occur frequently anywhere
along the limbus, at the
insertions of the rectus muscles,
and at the equator.
How are the sclera
and cornea similar?
How are they different?
Both are made up of collagen and are essentially avascular. The scleara is opqgue and white due to random collagen orientation and greater water content, while the cornea is clear because its collagen fibrils are arranged in an orderly fashion and its stroma is relatively dehydrated.
What path of extraocular extension
does choroidal melanoma take?
Scleral emissaria allow passage
of cells out of the globe.
Name the structures of the
anterior chamber angle from
anterior to posterior?
- Schwalbe’s line
- Trabecular meshwork
- Scleral spur
- Ciliary body
- Peripheral iris
Name the five structures in the limbus?
- Conjunctiva
- Tenon’s capsule
- Episclera
- Corneoscleral stroma
- Aqueous outflow apparatus
Where, anatomically, does the
cornea end and sclera begin?
At a plane connecting the
terminations of Descemet’s
and Bowman’s layers that
extends posteriorly to
Schlemm’s canal.
What geometric shape is the
trabecular meshwork in cross section?
What forms its corns?
Triangle. Its apex is
Schwalbe’s line. The corners
of the base are scleral spur
and ciliary body.
What are the three parts of the
trabecular meshwork and name
the part that is responsible for most
of the resistance to aqueous outflow?
- Uveal
- Corneoscleral
- Juxtacanalicular
The juxtacanalicular part is the
most resistant to aqueous outflow.
What area of the trabecular
meshwork is most pigmented?
Inferior chamber angle
What type of endothelium lines
the canal of Schlemm?
Nonfenestrated monolayer
of endothelial cells connected
by tight junctions.
Where is the thinnest part
of the iris located?
At its junction to the ciliary body,
the “iris root.”
What are posterior synechia?
Adhesions from the posterior
iris surface to the anterior
lens capsule.
What are peripheral anterior synechia (PAS)?
Adhesions of the anterior
peripheral iris to the posterior
peripheral cornea.
What structure lies where the
gonioscopic slit beam
converges to a point?
Schwalbe’s line
What is the normal adult
AP diameter of the lens up to
age 40? Equatorial diameter?
The AP diameter is 4-5 mm.
The Equatorial diameter is 9-10 mm.
What occurs during
accommodation?
The ciliary muscles contracts, decreasing zonular tension, increasing AP lens diameter, and increasing the refractive power of the lens. The pupil also constricts due to stimulation of the pupillary sphincter muscle. Both of these muscles are innervated by parasympathetic fibers.
What nourishes the lens
after regression of the
hyaloid vascular system?
Aqueous and vitreous
What is responsible for the
innervation of the lens?
Nothing.
The lens lacks innervation.
What is the PAS-positive
basement membrane of the
lens epithelial cells?
Lens capsule.
Where is the lens capsule
thickest? Thinnest?
It is thickest midway between
the anterior pole and equator.
It is thinnest at the posterior pole.
Where can you find
dividing lens epithelial cells?
Beneath the anterior and equatorial lens capsule. You will not find them under the posterior capsule. This is why extracapsular cataract extraction has the potential to leave a clear posterior capsule.
What causes posterior
capsular opacification
after cataract extraction?
Migration and proliferation
of lens epithelial cells across
the posterior capsule
What forms the lens sutures?
The anterior lens sutures are
formed from interdigitations of
apical lens fiber cell processes.
The posterior lens sutures are
formed from interdigitations of
basal cell processes.
Where do the zonules originate?
Where do they insert?
They originate from the basal laminae of the nonpigmented epithelium of the pars plana and pars plicata of the ciliary body in the valleys of the ciliary processes and insert on the lens capsule, anterior and posterior to the equator.
What three components
make up the uveal tract?
- Iris
- Ciliary body
- Choroid
What three places is the uveal tract
firmly attached to the sclera?
- Scleral spur
- Exit points of the vortex veins
- Optic nerve
Where is the pigmentation located
that is responsible for the iris color?
Anterior border layer
of the deep stroma.
What forms the bulk
of the iris stroma?
Blood vessels
What is the posterior pigmented
layer of the iris continuous with?
The nonpigmented epithelium
of the ciliary body and
neurosensory retina.
Describe physiologic ectropion.
The normal continuation of the posterior pigmented layer of the iris around the pupillary border and onto the anterior iris surface.
What type of stimulation causes the iris dilator muscle
to dilate?
Alpha2 adrenergic sympathetic stimulation
Describe the first order neuron
involved in sympathetic innervation
of the iris dilator muscle?
It originates in the ipsilateral
posterolateral hypothalamus,
travels through the brainstem
and synapses in the
intermediolateral gray matter
of the spinal cord at C8 and T2.
Describe the second order neuron
involved in sympathetic innervation
of the iris dilator muscle?
It leaves the spinal cord
at C8 and T2, and crosses over
the pulmonary apex, through
the stellate ganglion (no synapse)
and synapes in the superior
cervical ganglion.
Describe the third order neuron
involved in sympathetic innervation
of the iris dilator muscle?
It exits the superior cervical
ganglion, unites with the internal
carotid plexus, travels through the
cavernous sinus, joins V1 to enter
the orbit, and innervate the dilator
muscle of the iris.
The nerve to what muscle
carries the post-ganglionic
parasympathetic fibers
to the iris sphincter?
The nerve to the inferior oblique
from the inferior division of CNIII.
In what nucleus do the
parasympathetic fibers originate?
Edinger-Westphal
subnucleus within the midbrain,
lying ventral to the
aqueduct of Sylvius
Where does the ciliary body
attach to the sclera?
The base of the ciliary body
attaches to the scleral spur.
What are the two functions
of the ciliary body?
Aqueous humor formation
and accommodation.
Where is the pars plana located
in relation to the corneal limbus?
The pars plana is 3-4 mm
posterior to the surgical limbus.
What in the ciliary body is
responsible for maintaining the
blood-aqueous border?
The zonulae occludentes
along the apical border of the
nonpigmented epithelium.
How thick is the choroid?
0.25 mm
Describe the unique features
of choroidal blood flow?
The blood flow of the choroid
is high compared to other tissues.
Venous blood has only 2-3% less O2
than arterial blood.
Is Bruch’s membrane PAS-postitive?
Is it a true membrane?
Yes, it is PAS-positive.
No, it is not a true membrane.
What are the five layers
of Bruch’s membrane?
- Basal lamina of the RPE
- Inner collageous layer
- Middle collagenous layer
- Outer collagenous layer
- Basal lamina of the choriocapillaris
Is Bruch’s membrane
permealble to fluorescein?
Yes
What is a potential complication
of a break in Bruch’s membrane?
Subretinal choroidal
neovascular membranes.
What forms the outer
blood-retinal barrier?
Zonulae occludentes and
zonulae adherentes of the RPE.
What forms the inner
blood-retina barrier?
Endothelium of the
retinal blood vessels.
How are foveal RPE cells
different from extrafoveal RPE cells?
Foveal RPE cells are taller
and have more melanosomes
than their extrafoveal
counterparts. This is one of the
reasons that choroidal flush
is relatively dim under the
fovea during IVFA.
Where is drusen located
within the retina?
Between basement membrane
of the RPE and inner collagenous
layer of Bruch’s membrane.
Where is 90% of cones
found in the retina?
Almost all of the photoreceptors
in the fovea are cones, but 90% of
the total cones are found
outside the fovea.
A cilioretinal artery contributes
to some portion of retinal
circulation in what
percent of eyes?
30%
A cilioretinal artery contributes
to some portion of retinal
circulation in what
percent of people?
50%
A cilioretinal artery contributes
to some portion of macular circulation
circulation in what
percent of people?
15%
What do arterioles and
venules in the retina share
at their crossing?
They share a common basement
membrane. This is the reason
why AV nicking and venous
occlusions occur at AV crossing.
What forms the external limiting
membrane of the retina?
Attachment sites of adjacent
photoreceptors and Muller cells.
Axons of what cells form the
nerve fiber layer of the retina?
Ganglion cells
What forms the internal limiting
membrane of the retina?
What can happen if a break forms
in the internal limiting membrane?
Foot processes of
Muller cells. A break in
the internal limiting membrane
is necessary for epiretinal
membrane formation.
Are the external and internal
limiting membranes of the
retina true membrane?
No
Where is the retina the thickest?
How thick?
Papillomacular bundle.
0.23 mm
Where is the retina the thinnest?
How thin?
Foveola and Ora serrata.
0.10 mm & 0.11 mm respectively.
# Define the macula histologically and clinically.
Histologically, it is the area
where there is more than one
layer of ganglion cell nuclei.
Clinically, it is commonly thought
of as the area of retina between
the arcades.
What are the two major pigments
found in the macula lutea?
Zeaxanthin and lutein
create small yellow spots.
What type of pigment, when found
in the macula, can cause decreased
choroidal fluorescene under the
fovea?
Xanthophyll pigment.
What is the diameter
of the fovea?
1.5 mm = 1500 microns.
(equal to 1 disc diameter)
What is the foveola and
what is found there?
It is the central depression
in the fovea and is a.k.a
the umbo.
Only photoreceptors,
glial cells, & Muller cells
are found in the foveola.
What is the name for the
cysts found in paraffin sections
of the peripheral retina at
the ora serrata?
Blessig-Iwanoff cysts.
What is the weight, volume, and
make-up of the vitreous?
Weight- 4.0g
Volume 4.0 ml
Composition 99% water,
Hyaluronic acid is responsible for
the increased viscosity of the
vitreous compared to water.
How wide is the vitreous base
and where does it attach?
It is 6 mm wide. It extends 2 mm
anterior and 4 mm posterior to
the ora serrata.
What forms Cloquet’s Canal?
Regression of the hyaloid
vascularture before birth.
Which cranial nerve has the
distinction of having the fewest
number of fibers, being the only
one to completely decussate, and
being the only motor nerve to exit
the brainstem dorsally?
CN IV
An aneurysm of the anterior
communicating artery could
effect which crainial nerve?
Optic nerve.
Where is a common place for
the occurrence of aneurysms
that affect CN III?
At the junction of the
posterior communicating and
internal carotid arteries.
Macular fiber from which quadrant
cross anteriorly in the chiasm and
bulge into the contralateral optic
nerve? What is this bulge called?
Fibers from the inferonasal
macula form Wilbrand’s
anterior knee.
What artery most frequently
supplies the visual cortex?
The posterior cerebral artery.
What seven structures are found
within the cavernous sinus?
- Internal carotid artery
- The sympathetic plexus surrounding
the internal carotid artery - Cranial nerves III, IV, V1, V2, and VI
What three growth factors that
mediate the process of induction
in developing embryo have
been identified?
- Fibroblast growth factor (FGF)
- Insulin-like growth factor-I (IGF-I)
- Transforming growth factor-beta (TGF-β)
What is meant by the
term induction?
This term is used to
describe the process where
one tissue directs the development
of another tissue.
What is the name for the
master genes that control
the activity of other genes?
Homeobox genes.
These genes are found in
all plants and animals and
are conserved evolutionarily.
How many base pairs
compose homeobox genes?
180 base pairs.
What is the name for
the 60 amino acids encoded
by a homeobox gene?
Homeodomain.
How does the homeodomain
regulate gene expression?
These proteins bind to
specific DNA sequences on
other genes, causing either
activation or repression.
The homeodomain acts as a
set of transcription factors.
A mutation in the Pax-6
homeobox gene can
produce what ocular
abnormality can result?
Peter’s anomaly or
aniridia.
If the Pax-2 homeobox gene
contains a mutation, what
ocular abnormality can result?
Optic nerve coloboma
What is the name for the group
of anomalies resulting from defects
in the migration or terminal
differentiation of neural crest cells?
Neurocristophathies.
What four ocular structures
are derived from mesoderm?
- Extraocular muscles
- Schlemm’s canal
- Vascular endothelium
- Sclera, temporally
What 14 orbital and ocular
structures are derived from
neural crest?
- Cartilage - Connective tissue of EOM
- Corneal endothelium - Sclera, other than temporally
- Choroidal stroma - Trabecular meshwork
- Corneal stroma - Connective tissue of the orbit
- Ciliary body stroma
- Iris stroma
- Ciliary ganglions
- Meninges of the optic nerve
- Ciliary muscles
- Orbital bones
What eight ocular structures
are derived from neuroectoderm?
- Ciliary epithelium
- Neurosensory retina
- Iris posterior pigmented epithelium
- Optic nerve
- Iris dilator muscle
- Retinal pigment epithelium
- Iris sphincter muscle
- Vitreous
What ocular structures are
derived from surface ectoderm?
- Cilia
- Glands
- Conjunctival epithelium
- Lacrimal drainage system
- Corneal epithelium
- Lens
- Eyelids
- Vitreous
On what day of gestation
do the optic pits first appear?
Day 22 or 23
On what day of gestation does
the optic vesicle evaginate?
Day 25
On what day of gestation
is the lens placode induced
by the optic vesicle?
Day 27 or 28
On what day of gestation
does the embryonic
fissure closure?
Day 33
Where along the embryonic
fissure does closure begin?
Closure begins inferiorly
midway between the optic
nerve and iris and proceeds
anteriorly and posteriorly
simultaneously.
Complete fusion of the
embryonic fissures encloses
what artery within the globe?
Hyaloid artery
When does the retina
complete its development?
Remodeling of foveal
elements is not complete
until approximately
4 years of age.
What is the name for the
inner plexiform layer
of the retina prior
to its maturation?
Transient nerve fiber
layer of Chievitz.
How many optic nerve
axons are present at
16 weeks gestation?
3.7 million
How many optic nerve axons
are present at 33 weeks
gestation?
1.1 million which is
equal to the adult
number of axons
Primary lens fibers
form what part of the lens?
The embryonic nucleus.
By what day of gestation
have the primary lens fibers
filled the lens vesicle?
Day 45
During which month of
gestation do the eyelid folds
meet and fuse together?
Third month
During which month of
gestation do the eyelids
being to seperate?
Fifth month
During which month of
gestation does the hyaloid
vascular system begin
to regress? When is the
regression complete?
Begins in the fourth month.
Ends in the eighth month.
During which month of
gestation is the anterior
chamber angle completed?
Eighth month
During which month of
gestation do the retinal vessels
reach the temporal periphery?
Ninth month
What remains of the primary
vitreous in a normal adult?
Cloquet’s canal is the only
normal remant of the primary
vitreous. Bergmeister’s papilla
and Mittendorf’s dot
are two other common remants?
What structure does the
secondary vitreous become?
The main vitreous body.
The tertiary vitreous is
involved in the development
of what structure?
The zonular apparatus.
At what age is the adult
68° angle of ocular
alignment reached?
At about 3 years of age, the
globes reach their adult
orientation. At birth the
angle is 71°.
What is the name of the
substance or factor
that causes or increases the
incidence of physical anomalies
in a developing embryo?
Teratogen.
Name some classes of
nongenetic teratogens?
- Developmental failures
- Nutritional deficiencies
- Drugs
- Radiation
- Maternal infections
- Toxins
During which trimester
can teratogens cause
major orbital and ocular
structural abnormalities?
First trimester.
Exposure of the fetus to alcohol
during certain critical periods
can cause what ocular
abnormalities?
- Anterior lenticonus
- Microphakia
- Colobomas
- Microphthalmos
What is the name for
total absence of ocular tissue?
Anophthalmos. The diagnosis
of this very rare condition can
only be confirmed histologically.
Which type of anophthalmos
is lethal and why?
Secondary anophthalmos
is lethal because it is caused
by complete suppresion
of the development
of the forebrain.
What is name given to a
small, but otherwise
normal globe?
Nanophthalmos.
How can nanophthalmos
be inherited?
Autosomal dominant or
autosomal recessive.
What is name for a small
malformed globe?
Microphthalmos.
Most cases of clinical
anophthalmos are actually
severe cases of
microphthalmos.
How can nanophthalmos
be inherited?
Both via autosomal dominant
and autosomal recessive
inheritance.
Name two genetic aneuploidy
conditions that can result
in microphthalmos?
- Trisomy 13 (Patau syndrome)
- Trisomy 18 (Edwards syndrome)
What is name for a
single midline eye?
Cyclopia
Where is the proboscis
(primitive nose) located in true
cyclopia?
Above the midline
ocular structure
Is cyclopia compatible with life?
No. It is a lethal condition.
What is the name for the
condition caused when the
optic vesicles remain
in an embryonic state?
Cystic eye.
What is the name for the
condition that occurs when
faulty closure of the embryonic
fissure causes a remant of the
optic vesicle to be displaced
outside the globe?
Cystic coloboma
What is the name for a cystic
abnormality found in the orbit
that contains elements
from all primative germ layers?
Orbital teratoma
What is the name for a mass
of cerebral tissue protruding
through an orbital suture?
Encephalocele
What is the name for the
condition caused by failure
of the eyelid folds to form,
leaving a single layer of skin
lying over a usually
malformed eye?
Cryptophthalmos
In cryptophthalmos, where can
the eyebrows be found
if they are present at all?
Usually the eyebrows are
completely absent, but if
present, they will be
small and displaced
far temporally.
What causes the risk
trisomy to increase?
Increasing maternal age
What is the name
given to the meiotic
abnormality that leads to
monosomy or trisomy?
Nondisjunction
What is the only sex
chromosome aneuploidy
that is known to have
characteristic ocular finding?
Turner syndrome (45, X)
