BCSC Fundamentals Flashcards
What is the volume of each adult orbit?
30 cc
What are the seven bones of the bony orbit?
Frontal, Zygomatic, Maxilla, Ethmoid, Sphenoid, Lacrimal, Palatine
Which bones form the orbital roof?
Frontal bone and lesser wing of the sphenoid
Which bones form the medial wall of the orbit?
1) Frontal process of maxilla, 2) Lacrimal bone, 3) orbital plate of ethmoid, 4) Leser wing of sphenoid
Which bones form the orbital floor?
1) Maxilla, 2) Palatine, 3) Orbital plate of zygomatic
Which bones form the lateral orbital wall?
1) Zygomatic and 2) Greater wing of the sphenoid
What does the Whitnall tubercle indicate?
The site of attachment of 1) check ligament of LR muscle, 2) suspensory ligament of eyeball, 3) lateral palpebral ligament, 4) levator aponeurosis, 5) Whitnall ligament
What are the orbital foramina?
1) optic, 2) supraorbital, 3) anterior ethmoidal, 4) posterior ethmoidal, 5) zygomatic
Which structures are above the annulus of Zinn in the Superior Orbital Fissure?
lacrimal nerve of V1, frontal nerve of V1, CN IV, sup ophthalmic vein
Which structures are within the annulus of Zinn?
sup and inf divisions of CN III, nasociliary branch of V1, sympathetic roots of ciliary ganglion, CN VI
Which structures pass through the Inferior Orbital Fissure?
Infraorbital and zygomatic branches of V2, an orbital nerve from pterygopalatine ganglion, and inferior ophthalmic vein
What are the four sinuses?
Frontal, ethmoidal, sphenoid, maxillary
Which 3 roots does the ciliary ganglion receive?
1) long sensory root from nasociliary branch of V1, 2) short motor root from inf division of CN III, 3) sympathetic root from plexus around ICA
What is the 7th extraocular muscle?
Levator palpebrae superioris
List the rectus muscles in order of increasing distance of insertion from the limbus
1) MR (5.5), 2) IR (6.5), 3) LR (6.9), 4) SR (7.7)
What is the name for the curve passing through the rectus muscle insertions?
Spiral of Tillaux
Where does the superior oblique insert?
onto the sclera superiorly, under the insertion of the SR, after passing through the trochlea in the superior nasal orbital rim
What does the annulus of Zinn consist of?
The superior and inferior orbital tendons. It is the origin of the four rectus muscles
Where is the origin of the levator muscle?
lesser wing of the sphenoid, at the apex of the orbit, just superior to the annulus of Zinn
Where is the origin of the SO muscle?
periosteum of the body of the sphenoid bone, above and medial to the optic foramen
Where does the IO muscle originate?
from a shallow depression in the orbital plate of the maxillary bone, anteriorly
Which arteries supply the EOMs?
Inf and sup muscular branches of ophthalmic artery, lacrimal artery, and infraorbital artery
Which EOMs are innervated by the superior division of CN III?
levator and SR
Which EOMs are innervated by the inferior division of CN III?
MR, IR, IO
What type of fibers make up the EOMs?
both fast twitch and slow twitch fibers
What is the ratio of nerve fibers to muscle fibers in the EOMs?
1:3 (compared to 1:50 in skeletal muscle)
What is the normal size of the palpebral fissure?
27-30mm long, 8-11mm high
What is the excursion of the upper lid generated by the levator alone?
15mm (extra 2mm if using the frontalis in addition)
What are the segments of the eyelid (from dermal surface inward)?
skin, eyelid margin, subq tissue, orbicularis muscle, orbital septum, levator muscle, muller muscle, tarsus, conjunctiva
Where is the superior eyelid fold located?
at the upper border of the tarsus, at the initial insertion of the levator aponeurosis
What does the gray line of the eyelid margin indicate?
1) the most superficial portion of the orbicularis muscle, 2) the muscle of Riolan, and 3) the avascular plane of the lid
How many rows of eyelashes are there?
2 to 3
What are glands of Zeis?
modified sebaceous glands associated with the cilia
What are glands of Moll?
apocrine sweat glands of skin
Which CN innervates the orbicularis?
VII
Are meibomian orifices and lacrimal punctum anterior or posteiror to the gray line?
posterior
What are the two parts of the orbicularis?
Orbital and palpebral
Does the orbital part of the orbiclularis have involuntary functions?
No, only the palpebral part of the orbicularis does
What is the orbital septum?
a thin sheet of connective tissue that encircles the orbit as an extension of the periosteum of the roof and floor of the orbit
To which surface of the levator muscle does the orbital septum attach?
Anterior surface
How long is the levator muscle and its tendon?
muscle 40mm, muscle + tendon 50-55mm long
Which CN innervates the levator?
CN III
What is the Muller muscle?
A smooth, smypathetically innervated muscle originating from the undersurface of the levator muscle in the upper eyelid
How are the tarsal plates connected to the orbital margins?
by the medial and lateral palpebral ligaments
How much taller is the upper tarsus than the lower tarsus?
3x taller (11mm vs. 4 mm)
How many meibomian orifices are there at the eylid margin?
30 on upper lid, 20 on lower lid
What is distichiasis?
aberrant growth of cilia through the orificies of the meibomian glands
Is the palpebral conjunctival epithelium keratinized?
No
From which systems does the blood supply of the eyelids arise?
Facial (ECA) and Orbital (ICA)
Where does the marginal arterial arcade of the eyelid run?
between orbicularis and tarsus or within tarsus
What are the venous systems draining the eyelids?
Superficial/pretarsal system (IJ/EJ) and Deep/Posttarsal (cavernous sinus)
Are lymphatic vessels present in the eyelids?
Yes, but not in the orbit
Where do the lymphatics of the eyelids drain?
medial group drains to submandibular LNs, lateral group drains to preauricular LNs
Is the plica semilunaris a vestigial structure?
yes, it is analogous to the nictitating membrane of other animals
Are the lacrimal glands endocrine or exocrine?
Exocrine
What are the 2 cell types contained in the lacrimal gland?
1) Acinar cells lining the lumen, 2) Myoepithelial cells
What types of nerve fibers does the lacrimal gland receive?
cholinergic, VIP-ergic, sympathetic, and sensory from V1
What are three divisions of the conjunctiva?
Papebral, Forniceal, and Bulbar
Does the bulbar conjunctiva fuse with the Tenon capsule?
Yes
What is the Tenon capsule?
The Tenon capsule (fascia bulbi) is an envelope of elastic connective tissue that fuses posteriorly with the optic nerve sheath and anteriorly with the intermuscular septum, 3mm posterior to the limbus. The Tenon capsule is the cavity in which the globe moves.
From where do the anterior and posterior ciliary arteries arise?
the ophthalmic artery
What do the posterior ciliary arteries supply?
Whole uveal tract, cilioretinal artery, sclera, margin of cornea, adjacent conjunctiva
What do the anterior ciliary arteries supply?
SR, MR, IR muscles
What are the vortex veins?
Veins draining the choroid. There are usually 4-7 of vortex veins, at least 1 in each quadrant, exiting the eye just posterior to the equator.
What is the shape of the globe?
an oblate spheroid
What is the average transverse diameter of the adult eye?
24mm
What is the average volume of the adult globe?
6.5 to 7 cc
What are three things contained in tears aside from oil, water, and mucus?
immunoglobulins, lysozyme, and lactoferrin
What is the power of the anterior surface of the cornea?
49D
What structure attaches the basal epithelium of the cornea to the epithelial basement membrane?
hemidesmosomes
What non-epithelial cells are found in the corneal epithelium?
Histiocytes, macrophages, lymphocytes, pigmented melanocytes, and Langerhans cells
Is Bowman layer replaced after injury?
No
How thick is Bowman layer?
8-14 microns thick
What types of collagen are found in the corneal stroma?
Types I, III, V, and VI
What percent of the corneal volume is made up by keratocytes?
5%
Where is the density of keratocytes highest in the corneal stroma?
Anteriorly
What is the Descemet membrane?
The basement membrane of the corneal endothelium.
What are peripheral excrescences in the Descemet membrane called?
Hassal-Henle warts (common in the elderly), as opposed to Guttae (which are central)
Which way does the apical surface of a corneal endothelial cell face?
Toward the anterior chamber
Are desmosomes seen between corneal endothelial cells?
No, but junctional complexes are present between contiguous cells
Where is the sclera the thinnest?
at the insertions of the rectus muscles (0.3mm)
Where is the sclera the thickest?
around the optic nerve head (1mm)
What are included in the corneal limbus?
Conjunctiva and limbal palisades, Tenon capsule, episclera, corneoscleral stroma, aqueous outflow apparatus
What are the two parts of the surgical limbus?
1) anterior bluish gray zone from Bowman termination to Descemet termination, 2) Posterior white zone from Descemet termination (Schwalbe line) to scleral spur
What are conditions that cause an increase in the depth of the anterior chamber?
aphakia, pseudophakia, and myopia
What is the normal volume of the anterior chamber?
200 microliters
What are the two primary means of aqueous drainage?
Schlemm canal and uveoscleral pathway
What is the trabecular meshwork?
a circular spongework of connective tissue lined by trabeculocytes
What are the 3 layers of the TM?
1) Uveal portion, 2) Corneoscleral meshwork, 3) Juxtacanalicular tissue
Which portion of the TM provides the most resistance to outflow?
Juxtacanalicular connective tissue
What are the 3 points of connection of the uvea to the sclera?
1) Scleral spur, 2) Vortex veins, 3) optic nerve
How is aqueous drained via Schlemm canal?
25-30 collector channels arise from the canal and drain into the deep and intrascleral venous plexuses, which in turn drain to the episcleral venous plexus. 8 of the collector channels drain directly to the episcleral venous plexus as “aqueous veins.”
What does eye color correspond to?
The amount of pigment in the anterior border layer and deep stroma of the iris.
What is the orientation of the fibers of the pupillary sphincter muscle?
circular (adjacent to pupillary border)
What is the orientation of the fibers of the iris dilator muscle?
radial (peripheral)
What type of innervation does the iris dilator muscle have?
Both sympathetic and parasympathetic! Cholinergic parasympathetic innervation may inhibit the contraction of the dilator muscle
What is the primary innervation of the iris sphincter muscle?
Parasympathetic innervation from nucleus of CN III. It appears to also have secondary sympathetic innervation that inhibits contraction (and thereby inhibits pupillary constriction).
What are the two primary functions of the ciliary body?
aqueous humor formation and lens accommodation
How far from the corneal limbus is the pars plana of the ciliary body?
3-4mm posterior
Which is more vascular, the pars plana or the pars plicata of the ciliary body?
the pars plicata is richly vascularized
What is the lining of the ciliary body?
2 layers of epithelial cells (non-pigmented and pigmented epithelial layers)
What is the main arterial supply of the ciliary body?
the anterior ciliary arteries and long posterior ciliary arteries
What are the three layers of fibers in the ciliary muscle?
1) longitudinal, 2) radial, 3) circular
What is the primary innervation of the ciliary body?
Parasympathetic fibers from CN III via the short ciliary nerves
What do cholinergic drugs do to the ciliary body muscle?
They cause it to contract, which opens up the TM via its attachments to the sceral spur, thereby increasing aqueous outflow
Where does the perfusion of the choroid come from?
The short posterior ciliary arteries and the perforating anterior ciliary arteries
In to what does blood from the choroid drain?
The vortex veins
What is Bruch membrane?
A PAS-positive layer resuting from the fusion of the basal laminae of the RPE and choriocapillaris
What are the layers of the Bruch membrane?
1) basal lamina of RPE, 2) inner collagenous zone, 3) porous band of elastic fibers, 4) outer collagenous zone, 5) basal lamina of the choriocapillaris
Is Bruch membrane permeable to fluorescein?
Yes
Are the medium and large choroidal vessels permeable to fluorescein?
No, but the choriocapillaris is
On what does the degree of fundus pigmentation viewed ophthalmoscopically depend?
The number of pigmented melanocytes in the choroid
Does the degree of pigmentation of the choroid affect photocoagulation?
Yes
What is the diameter of the lens in the adult?
9-10mm
What is the depth of the lens in the adult?
5-6mm
What is the lens capsule?
A basal lamina put down by the lens epithelial cells, rich in type IV collagen
Does the thickness of the anterior capsule change during life?
Yes, it continues to grow, while the posterior capsule does not
Is lens epithelium present underneath the posterior capsule?
No
What is the germinative zone of the lens?
A set of peripheral meridional rows of cuboidal pre-equatorial lens epithelial cells that undergo mitotic division
Of what material are lens zonules made?
fibrillin
What is the average diameter of the macula?
5-6mm
What is the composition of the RPE?
A monolayer of hexagonal cells
What are the functions of the RPE?
1) Vitamin A metabolism, 2) maintenance of outer blood-retina barrier, 3) phagocytosis of outer segments, 4) absorption of light, 5) heat exchange, 6) formation of basal lamina, 7) production of MPS matrix, 8) active transport into and out of RPE
What is a retinal detachment?
separation of the neurosensory retina from the RPE
From what do lipofuscin granules arise?
the discs of photorecptor outer segments. They represent residual bodies arising from phagosomal activity
What are phagosomes?
membrane-enclosed packets of disc outer segments that have been engulfed by the RPE
What surrounds the photoreceptor outer segments?
An MPS matrix, secreted by the RPE
What types of cells are found in the inner nuclear layer?
Bipolar, Amacrine, and Horizontal cells; (also, Muller-type glial cells)
What types of cells are found in the outer nuclear layer?
Photoreceptor cell bodies
How many rods and cones are there?
120M rods, 6M cones
What is the blood supply of the inner retina?
Branches of the cnetral retinal artery and, in 30% of people, a cilioretinal artery branching from the ciliary circulation
Are retinal arteries permeable to fluorescein?
No, they have tight junctions and maintain the blood-retina barrier
Is the external limiting membrane fenestrated?
Yes
What is the OPL called in the fovea?
the Henle fiber layer
Is the OPL thicker in the macula?
Yes
Of what does the OPL consist?
Photoreceptor axons
Of what does the IPL consist?
axons of bipolar and amacrine cells, as well as the dendrites of ganglion cells
Of what does the NFL consist?
axons of the ganglion cells
Are axons of ganglion cells myelinated?
Not within the eye. They are myelinated only after they pass through the lamina cribrosa
What is the histologic definition of the macula?
The region with more than 1 layer of ganglion cell nuclei (plus the foveola)
What are the two major pigments of the macula?
zeaxanthin (cone-dense areas) and lutein (rod-dense areas)
What is the diameter of the fovea?
1.5mm
What is the diameter of the foveola?
0.35mm
Which layers are absent in the foveola?
NFL, GCL, IPL, INL
Is the FAZ different from the foveola?
It is roughly the same size and location, but characterized only by its avascularity
What type of photoreceptors are present in the foveola?
ONLY cones
How far from Schwalbe line is the the ora serrata?
5.75mm to 6.5mm
Of what does the vitreous consist?
99% water, plus MPS and hyaluronic acid
What is the path of the fibers forming CN I?
from olfactory receptors in mucous membrane of the nose to the olfactory bulb (where they form the nerve)
What are the 4 topographic areas of the optic nerve?
1) Intraocular region, 2) Intraorbital region, 3) Intracanalicular region, 4) Intracranial region
What is the averatge length of the optic nerve?
40mm (35-55mm)
What is the length of the intraorbital portion of the optic nerve?
25-30mm, via a sinuous course
What is the average size of the optic disc?
1.5mm (horizontal) x 1.75mm vertical
What are the 4 parts of the optic nerve?
1) superficial nerve fiber layer, 2) prelaminar area, 3) laminar area, 4) retrolaminar area
Where within the optic nerve head are fibers from the macula?
Lateral
How do ganglion cell axons pass through the lamina cribrosa?
in fascicles formed by astrocytic glial cells
What leads to enlargement of the optic cup?
Loss of ganglion cell axons and supporting glial elements
How many tissue plates are in the lamina cribrosa?
10
What percent of the optic nerve head volume is made up by astrocytes?
10%
What types of collagen are found in the lamina cribrosa?
Type I and Type III, in addition to elastin, laminin, and fibronectin
What are the functions of the lamina cribrosa?
1) scaffold for optic nerve axons,2) point of fixation for CRA and CRV, 3) reinformcement of posterior segment of globe
What is the diameter of the optic nerve posterior to the lamina cribrosa?
3mm (increases due to myelination of nerve fibers)
What happens to the dural sheath of the optic nerve at the optic canal?
It fuses to the periosteum, completely immobilizing the nerve
What divides the nerve into fascicles?
The pia mater
What is the blood supply of the optic nerve in the optic canal?
Pial vessels from the ophthalmic artery
What is the blood supply of the retrolaminar nerve?
Pial vessels and short posterior ciliary vessels, CRA, and recurrent choroidal arteries
What is the blood supply of the lamina cribrosa?
The short posterior ciliary arteries and branches of the arterial circle of Zinn-Haller
What is the blood supply of the prelaminar nerve?
short posterior ciliary arteries (and cilioretinal artery if present) and possibly recurrent choroidal arteries
What is the blood supply of the NFL?
the CRA
What is the blood supply of the intracanalicular nerve?
ophthalmic artery
What is the blood supply of the intracranial optic nerve?
ICA and ophthalmic artery
What percent of the volume of the optic nerve consists of macular nerve fibers?
80%
Which layers of the LGN receive fibers from the contralateral optic nerve?
1, 4, and 6
What gives rise to the upper homonymous “pie in the sky” defect?
Damage to the optic radiation in the anterior temporal lobe
What is the blood supply of the visual cortex?
The posterior cerebral artery
What does CN III supply?
SR, MR, IR, IO, levator palpebrae, pupillary sphincter, and ciliary muscle
Which nucleus of CN III provides innervation to the ciliary muscle and pupillary sphincter?
The Edinger-Westphal nucleus
Where does CN III divide into superior and inferior divisions?
Usually after passing through the annulus of Zinn in the orbit (sometimes within the cavernous sinus)
What is a sensitive early sign of compression of CN III?
loss of pupillary constriction ability
What is the path of the pupillary light reflex?
light activates photoreceptors –> retinal ganglion cells –> axons cross in the optic chiasm –> in optic tract, pupillary fibers leave visual fibers and go to pretectal nuclei at superior colliculus –> efferents to EW nuclei with partial decussation –> parasympathetic fibers leave from each EW nucleus and join CN III –> fibers join inferior division of CN III –> synapse in ciliary ganglion –> give rise to short ciliary nerves (3%-5% are pupillomotor)
What is the path of the pupillary near reflex?
reflex initiated in occipital association cortex –> relay inpretectal and tegmental areas –> pass to EW nuclei, motor nuclei of MR muscles, and nuclei of CN VI –> efferents to MR, LR, pupillary sphincter, and ciliary muscle
What actions are involved in the near reflex?
1) Accommodation, 2) Pupil constriction, 3) converence
Which CN has the longest intracranial course?
CN IV (75mm)
Which CN is the only CN to be completely decussated?
CN IV
Which CN is the only CN to exit dorsally from the brainstem?
CN IV
Does CN IV enter the orbit through the annulus of Zinn?
No, it enters the orbit through the superior orbital fissure outside the annulus of Zinn
What are the 4 nuclei of the CN V nuclear complex?
1) mesencephalic nucleus, 2) main sensory nucleus, 3) spinal nucleus and tract, 4) motor nucleus (in the pons)
What does the main sensory nucleus of CN V receive?
light touch from the skin and mucous membranes
What does the spinal nucleus of CN V receive?
pain and temperature, as well as cutaneous components of CN VII, IX, and X
What does the mesencephalic nucleus of CN V receive?
prioprioception and deep sensation from masticatory, facial, and extraocular muscles
Which muscles does the motor nucleus of CN V innervate?
muscles of mastication (pterygoid, masseter, temporalis), tensor tympani, tensor veli palatini, mylohyoid, anterior belly of digastric
Where is the trigeminal ganglion located?
in Meckel cave, a recess near the apex of the petrous part of the temporal bone in the middle cranial fossa. It is posterolateral to the cavernous sinus.