Periorbita and orbital fibroadipose tissue Flashcards
What is the volume of each orbital cavity?
30cm3
What binds together and supports the orbital contents?
fibroadipose tissue
What are 5 separate components into which the orbital contents can be divided?
- Periorbita
- Bulbar fascia (Tenon’s capsule)
- Muscular fascial sheaths
- Medial and lateral check ligaments
- Suspensory ligament (of Lockwood)
What is another term for the periorbita?
periosteum of the orbit
What is the periorbita?
layer of connective tissue tightly bound to the bones only at the sutures, fissures and foraminae in the orbital walls
What are the 2 layers that the periorbita is frequently described as having?
- Dense outer layer
- Looser inner layer
What 2 structures are invested by the looser inner layer of the periorbita?
- Orbital nerves
- Lacrimal gland
What are the 4 places where the periorbita is tightly bound to the bones?
- Sutures
- Fissures
- Foraminae
- Posterior lacrimal crest - covers lacrimal sac and is continuous with the fibrous lining of the nasolacrimal duct
What is the connection between the periorbita and the lacrimal sac?
the periorbita is tightly bound to the posterior lacrimal crest where it covers the lacrimal sac and is continuous with the fibrous lining of the nasolacrimal duct
What is the periorbita like at the inferior and superior orbital fissures?
it forms a dense membrane over them, with sufficient gaps for transmission of nerves and vessels
What 3 structures is the periorbita continuous with?
- the periosteum lining the optic foramen
- the sheath of the optic nerve, itself an extension of the dura mater of the brain
- the orbital septum (palebral fascia) in the eyelids anteriorly
Where is the periorbita attached anteriorly?
at the orbital margins, becomes continuous with the orbital septum (palpebral fascia) in the eyelids
What structure is the periorbita continuous with anteriorly?
orbital septum (palpebral fascia) in the eyelids
What is the bulbar fascia (Tenon’s capsule)?
thick fibrous sheath enclosing the globe but separated from it by a layer of loose connective tissue
What are the muscular fascial sheaths?
surround the extraocular muscles and blend with the bulbar fascia
Label the folowing on the image: periorbita, bulbar fascia, muscular fascial sheaths, medial and lateral check ligaments, suspensory ligament (of Lockwood)
What connects the four rectus muscles?
fibrous intermuscular membrane (common muscle sheath)
What space is created by the fibrous intermuscular membrane connecting the four rectus muscles?
intraconal space
Where is the intraconal space best developed, and where is it incomplete?
best developed in anterior part of orbit
incomplete behind the globe
What exists besides the ‘check’ ligaments and where?
other specific attachments via fibrous bands to the orbital walls throughout their course
What is the ‘active pulley hypothesis’?
postulates a crucial role for connective tissue bands (including check ligaments) that provide attachments via fibrous bands to the orbital walls;
they are known as ‘pulley suspensions’ and concerns understanding the kinematics of extraocular muscle action
Where do the suspensions of check ligaments and other connective tissue bands pass?
between the orbital wall and the ‘pulley sleeve’ of each muscle, which is described as a ring-like extension of the connective tissue from Tenon’s capsule posteriorly around the muscle
What controls the tone of the pulleys concerned in the active pulley hypothesis?
possibly under neuronal control because of the presence of smooth muscle fibres
What does the active pulley hypopthesis propose?
that the rectus muscles have an orbital layer of muscle fibres that are continuous with (or ‘blend with’ or ‘insert into’) the pulley sleeves (and thus also into the pulley suspensions), in essence one part of a bifid insertion
the inner half or global layer of the rectus muscle continues through the sleeve and bulbar fascia to insert directly into the sclera
newly postulated function for orbital connective tissue: dual insertion allows pulleys to act as a second origin and influence direction of pull of EOMs
