Anatomy Flashcards
Which wall of the orbit provides the shortest most direct path to the optic nerve
The medial wall of the orbit
Which bone in the orbit houses the optic canal
The lesser wing of the sphenoid bone houses the optic canal.
Why do patients with retrobulbar neuritis experience pain with eye movements?
At the annulus of Zinn, the medial and superior rectus muscles are adjacent to the
optic nerve sheath. Because of this anatomical relationship, patients with retrobul-
bar optic neuritis experience pain with eye movement
What is the volume of the orbit
30mls
What are the dimensions of the entrance of the orbit
35mm height 45mm width with the widest part of the orbit 1cm behind the anterior orbital margin
What is the depth of the orbit
40-45mm depending on whether the measurement is made along the medial/lateral wall
Which bones make up the orbit
Frontal
Zygomatic
Sphenoid
Ethmoid
Palatine
Lacrimal
Maxilla
Which bones make up the orbital roof
orbital plate of the frontal bone
lesser wing of the sphenoid bone
Which bones make up the medial orbital wall
- frontal process of the maxillary bone
- lacrimal bone
- orbital plate of the ethmoid bone
- lesser wing of the sphenoid bone
What bone corresponds to the lamina papyracea
Orbital plate of ethmoid bone
What are the bones of the lateral orbital wall
- zygomatic bone
- greater wing of the sphenoid bone
What are the bones of the orbital floor
- orbital plate of the maxillary bone
- palatine bone
- orbital plate of the zygomatic bone
Where does the inferior oblique muscle originate from
From a depression on orbital floor near orbital rim (maxilla). Only muscle not coming from orbital apex
The lateral orbital wall has Whitnall tubercle/lateral orbital tubercle which is the point of attachment for what structures?
- check ligament of the lateral rectus muscle
- suspensory ligament of the eyeball (Lockwood suspensory ligament)
- lateral canthal tendon
- lateral horn of the levator aponeurosis
What does the supraorbital foramen transmit?
blood vessels and the supraorbital nerve, which is an extension of the frontal nerve, a branch of the ophthalmic division (V1) of cranial nerve V (CN V, the trigeminal nerve)
Where is the anterior ethmoidal foramen located?
At the frontoethmoidal suture
What does the anterior ethmoidal foramen transmit?
anterior ethmoidal vessels and nerve
Where does the posterior ethmoidal foramen lie?
at the junction of the roof and the medial wall of the orbit
What does the posterior ethmoidal foramen transmit?
transmits the posterior ethmoidal vessels and nerve through the frontal bone
Where do the zygomaticotemporal and zygomaticofacial foramen lie?
in the portion of the lateral orbital wall formed by the zygomatic bone and transmit vessels and branches of the zygomatic nerve
How long is the superior orbital fissure?
It is approximately 22 mm long and is spanned by the tendinous ring formed by the common origin of the rectus muscles (annulus of Zinn)
What structures does the superior orbital fissure transmit?
- lacrimal nerve of CN V1
- frontal nerve of CN V1
- CN IV (trochlear nerve)
- superior ophthalmic vein
What structures traverse the Annulus of Zinn
- superior and inferior divisions of CN III (the oculomotor nerve)
- nasociliary branch of CN V1, which also carries the postganglionic sympathetic
fibers en route to the ciliary ganglion - CN VI (the abducens nerve)
Where does the inferior ophthalmic vein travel?
The course of the inferior ophthalmic vein is variable, and it can travel within or below the ring as it exits the orbit.
What does the inferior orbital fissure transmit?
*infraorbital and zygomatic branches of CN V2,
*an orbital nerve from the pterygopalatine ganglion,
*the inferior ophthalmic vein
How does the inferior ophthalmic vein drain?
The inferior ophthalmic vein connects with the pterygoid plexus before draining into the cavernous sinus.
What is the fovea ethmoidalis
forms the roof of the ethmoid sinuses, is a lateral extension of the cribriform plate.
Where is the ciliary ganglion located?
approximately 1 cm in front of the annulus of Zinn, on the lateral side of the ophthalmic artery, between the optic nerve and the lateral rectus muscle
What are the 3 roots of the ciliary ganglion?
A long (10–12-mm) sensory root from the nasociliary branch of CN V1
A short motor root arises from the inferior division of CN III.
A short motor root arises from the inferior division of CN III.
What do the short ciliary nerves supply?
The short ciliary nerves are both sensory and motor nerves, carrying autonomic fibers to the pupil and ciliary muscles
How many extraocular muscles are there?
7
- medial rectus
- lateral rectus
- superior rectus
- inferior rectus
- superior oblique
- inferior oblique
- levator palpebrae superioris
Where does the levator palpebrae superioris muscle arise from?
the lesser wing of the sphenoid bone, at the apex of the orbit, just superior to the annulus of Zinn
Where does the superior oblique muscle originate from?
the periosteum of the body of the sphenoid bone, above and medial to the optic foramen
Largest and Smallest Muscle size?
Largest -LPS
Smallest- IO
Longest and Shortest Muscle tendon?
Longest- SO
Shortest- IO
Which muscles are innverated by inferior division of CN3
MR
IR
IO
Which muscles are innervated by superior division of CN3
SR
LPS
Where does the SO muscle insert on the eye
onto the sclera superiorly, under the insertion of the superior rectus.
Where does the IO muscle insert on the eye
The inferior oblique muscle inserts onto the sclera in the posterior inferotemporal quadrant.
Which blood vessels supply the extraocular muscles
- muscular branches of the ophthalmic artery
- infraorbital artery
- lacrimal artery
Which muscles receive blood supply from muscular branches of the ophthalmic artery?
The muscular branches of the ophthalmic artery give rise to the anterior ciliary arteries and can be divided into lateral (superior) and medial (inferior) branches. Each rectus muscle has 1–4 anterior ciliary arteries, which eventually pass through the muscle belly; penetrate the sclera, anastomosing with the major arterial circle; and contribute to the blood supply of the anterior segment
Which muscles receive blood supply from the lacrimal artery
The lateral rectus muscle receives part of its blood supply from the lacrimal artery;
Which muscles receive blood supply from infraorbital artery
The inferior oblique and inferior rectus muscles receive part of their blood supply from the infraorbital artery
What is the ratio of nerve firbres to muscle fibres in the extraocular muscles?
1:3 to 1:5 compared to skeletal muscle which is 1:50 to 1:125
Which fibres are useful for smooth pursuit movements?
slow, tonic-type fibers (en grappe)
Which fibres are useful for rapid saccadic movements?
fast, twitch-type fibers (en plaque)
What is the blood supply to the orbit?
Posterior and Anterior Ciliary Arteries
How many short posterior ciliary arteries enter the orbit
Approximately 16–20 short posterior ciliary arteries and 6–10 short ciliary nerves enter the globe in a ring around the optic nerve
What do the 2 long posterior ciliary arteries supply?
2 long posterior ciliary arteries and 2 long ciliary nerves enter the sclera on either side of the optic nerve, close to the horizontal meridian. They course anteriorly in the suprachoroidal space, terminating at the major arterial circle of the iris.
Where do the posterior ciliary arteries originate from and what do they supply?
The posterior ciliary vessels originate from the ophthalmic artery and supply the entire uvea, the cilioretinal arteries, the sclera, the margin of the cornea, and the adjacent conjunctiva. Occlusion of the posterior ciliary vessels (as in giant cell arteritis) may have profound consequences for the eye, such as anterior ischemic optic neuropathy.
Where do the anterior ciliary arteries originate from and what do they supply?
The anterior ciliary arteries also arise from the ophthalmic artery and usually supply (in pairs) the superior, medial, and inferior rectus muscles. After emerging from the surface of the rectus muscles, the anterior ciliary vessels perforate the sclera anterior to the rectus muscle insertions, where they anastomose with the long posterior ciliary arteries at the major arterial circle of the iris.
What arrangement do the iris vessels have which help distinguish them from NVI?
Radial arrangement
How is the eye blood drained?
The vortex veins drain the venous system of the choroid, ciliary body, and iris. Each eye contains 4–7 (or more) veins.
What is the interpalpebral fissure height?
27–30 mm long and 8–11 mm wide
How high can the LPS raise the eyelid
15mm and can be raised another 1–2 mm by the action of the Müller muscle
Eyelid from the surface to inwards layers?
- skin and subcutaneous connective tissue
- muscles of protraction (orbicularis oculi muscle, the main protractor)
- orbital septum
- orbital fat
- muscles of retraction (levator palpebrae superioris, Müller muscle, capsulopalpebral fascia, inferior tarsal muscle)
- tarsus
- conjunctiva
What does the eyelid crease signify?
A superior eyelid crease is present near the upper border of the tarsus, where the levator aponeurosis establishes its first insertional attachments.
Is the superior punctum located more or less medially than the inferior punctum
More medially
What does the gray line on the eyelid correspond to?
histologically to the most superficial portion of the orbicularis oculi muscle, the muscle of Riolan, and to the avascular plane of the eyelid. Anterior to this line, the eyelashes (or cilia) arise, and behind this line are the openings of the meibomian (or tarsal) glands just anterior to the mucocutaneous junction.
Which eye glands are Exocrine?
Lacrimal (orbital and palpebral) —>AQUEOUS
Accessory Lacrimal (Plicae, caruncle) —>AQUEOUS
Wolfring and Krause (Eyelids)—>AQUEOUS
Which eye glands are Holocrine?
Meibomian (Tarsus) –> OIL
Zeis (Follicles of cilia,eyelid, caruncle) –> OIL
Goblet cell (Conjunctiva plicae, caruncle) –> MUCUS
Which eye glands are Apocrine?
Moll (Eyelid) —> SWEAT
How many fat pads are posterior to the superior vs inferior septum?
2 behind the superior septum and 3 behind the inferior septum
What is the Whitnall ligament?
formed by a condensation of tissue surrounding the levator muscle. It provides support for the upper eyelid and surrounding tissues. At the Whitnall ligament, the levator muscle transitions into the aponeurosis anteriorly and the Müller (superior tarsal) muscle posteriorly. The Whitnall ligament is also where the levator muscle’s anterior–posterior vector changes to superior–inferior, toward the aponeurosis.
How many mm of upper lid lift does the Muller muscle do?
1-2mm
The Müller muscle attaches to the upper border of the upper tarsus and to the conjunctiva of the upper fornix
What are the retractors of the lower eyelid?
The capsulopalpebral fascia, which is analogous to the levator aponeurosis in the upper eyelid, and the inferior tarsal muscle.
What is the Lockwood ligament?
The inferior equivalent to the Whitnall ligament is the suspensory ligament of Lockwood:
A fusion of the sheath of the inferior rectus muscle,
The inferior tarsal muscle, and
The check ligaments of the medial and lateral rectus muscles
How many meibomian glands in the Upper lid vs lower lid
A single row of 30–40 meibomian orifices is pres- ent in the upper eyelid, but there are only 20–30 orifices in the lower eyelid.
What is the blood supply to the eyelids?
The blood supply of the eyelids is derived from the facial system, which arises from the external carotid artery, and the orbital system, which originates from the internal carotid artery along branches of the ophthalmic artery.
Thus, the eyelid vasculature represents an anastomosis of the external and internal carotid arteries
Which blood vessel is important in DCR?
Angular artery
Where is the marginal arterial arcade supplying the eyelids located?
It is either between the tarsal plate and the orbicularis oculi muscle or within the tarsus
Where is the smaller peripheral arterial arcade supplying the eyelids located?
A smaller peripheral arterial arcade runs along the upper margin of the tarsal plate anterior to the Müller muscle
What is the terminal branch of the ECA
The superficial temporal artery
What is the venous drainage of the eyelids
2 components: a superficial (or pretarsal) system, which drains into the internal and external jugular veins, and a deep (or posttarsal) system, which flows into the cavernous sinus.
Thus, the venous circulation of the eyelid connects the face with the cavernous sinus, providing a route for the spread of infection.
Which lymphatics drain the eyelids
Lymphatic drainage from the eyelids parallels the course of the veins. There are 2 groups of lymphatics:
* a medial group that drains into the submandibular lymph nodes
* a lateral group that drains into the superficial preauricular lymph nodes
Where is the lacrimal gland located?
The main lacrimal gland is located in a shallow depression within the orbital part of the frontal bone.
What joins the orbital and palpebral lacrimal gland?
An isthmus
What types of cells do the lacrimal glands consist of?
- glandular epithelial cells, which line the lumen of the gland
- myoepithelial cells, which surround the parenchyma and are covered by a basement
membrane
What do lacrimal secretions consist of?
lysozymes, lactoferrin, and immunoglobulin A.
What is the blood supply to the lacrimal gland?
The lacrimal artery, a branch of the ophthalmic artery, supplies the gland with blood
What kind of nervous supply does the lacrimal gland receive?
The lacrimal gland receives secretomotor cholinergic, vasoactive intestinal polypeptide (VIP)ergic, and sympathetic nerve fibers in addition to sensory innervation via the lacrimal nerve (from CN V1).
The gland’s extremely complex neuroanatomy governs both reflex and psychogenic stimulation
What percentage of lacrimal secretions do the Accessory lacrimal glands of Wolfring and Krause contribute to?
10%
Which part of the orbicularis oculi muscle drives tears into the cannaliculi
Fibers of the tarsal orbicularis oculi muscles surround the canalicular system and lacrimal sac
Length of cannaliculus
8-10mm
Length of nasolacrimal sac
12-15mm
Length of nasolacrimal duct
12-18mm
What epithelium are the lacrimal puncta and cannaliculi lined with?
stratified squamous non keratinized epithelium that merges with the epithelium of the eyelid margins.
Near the lacrimal sac which epithelial cell type does the epithelium differentiate into?
- a superficial columnar layer
- a deep, flattened cell layer
What are the 3 zones of conjunctiva
Palpebral (Tarsal)
Bulbar
Forniceal
What is the blood supply to the conjunctiva?
Anterior ciliary arteries supply blood to the bulbar conjunctiva. The palpebral conjunctiva is supplied by branches of the marginal arcades of the eyelids.
How many cell layers thick is the conjunctival epithelium?
2-5 cell layer thick
Where are the goblet cells mainly found in the conjunctiva?
The goblet cells (unicellular mucous glands) are concentrated in the inferior and medial portions of the conjunctiva, especially in the region of the caruncle and plica semilunaris. They are sparsely distributed throughout the remainder of the conjunctiva and are absent in the limbal region.
What is the caruncle?
The caruncle is a small, fleshy, ovoid structure attached to the inferomedial side of the plica semilunaris. As a piece of modified skin, it contains sebaceous glands and fine, colorless hairs. The surface is covered by nonkeratinized stratified squamous epithelium
What is the plica semilunaris?
The plica semilunaris is a narrow, highly vascular, crescent-shaped fold of the conjunctiva located lateral to and partly under the caruncle. Its lateral border is free and separated from the bulbar conjunctiva, which it resembles histologically. The epithelium of the plica is rich in goblet cells. The plica’s stroma contains fat and some nonstriated muscle. The plica is a vestigial structure analogous to the nictitating membrane, or third eyelid, of dogs and other animals.
