Week 5 - Orbit anatomy Flashcards
Which bone makes the superior orbital ridge?
-Frontal
Which bone makes the inferior orbital ridge?
-Zygomatic and maxilla
Name the boundaries of the orbit
- Apex = optic canal
- Superior = Frontal and Sphenoid
- Lateral = zygomatic and sphenoid
- Medial = ethmoid, maxillary, lacrimal and sphenoid
- Inferior = maxillary and zygomatic
Which boundary of the orbit is the thinnest?
-Medial
What runs through the optic canal?
- Optic nerve
- Ophthalmic artery
Name the foramina of the bony orbit
In which bone do they lie?
- Optic canal
- Superior orbital fissure
- Inferior orbital fissure
- Sphenoid
What runs through the superior orbital fissure?
- CNIII
- CNIV
- CNV1
- CNVI
- Superior ophthalmic vein
What is a blow out fracture? How does it present? How is it treated?
- Fracture to the inferior border of the orbit causing inferior rectus (and other muscles) to herniate into maxillary sinus
- Patient will have a history of blow to the eye and will be unable to look up
- Steroids and antibiotics (sometimes requires surgery)
Why is it crucial the iris is able to contract and dilate?
- Allow different amounts of light into the eye
- Dilates in the dark to allow more light to enter
- Contracts in the light to prevent too much light from entering and damaging the retina
What is the function of the lens?
-Focus the light into the retina
Name the 3 layers of the eyeball and their constituents
- Outer fibrous -> Cornea, Sclere
- Middle vascular -> Ciliary body, Iris, choroid
- Inner -> retina, macula
Why is there a blind spot in the eye?
-optic disk where optic nerve enters
What is visual acuity?
-Clarity of vision
What is the ciliary body?
- Part of the eye which includes the ciliary muscle.
- Accommodation (involving contracting/relaxing the iris) and produces/resorps aqueous humor
What is the retina?
-Inner most layer of the eye which contains photoreceptors (cones and rods) which transmit chemical and electrical impulses down optic nerve
What is the sclera?
-White of the eye -> Protective fibrous layer of the eye containing collagen and elastic fibres
What is the choroid?
- Vascular layer of the eye containing connective tissue which lays between retina and sclera
- Functions to provide oxygen and nourishment to the outer layers of the eye
What is the macula?
-Oval shaped pigmented area of retina which is the place of most visual acuity
What is accommodation?
-Changes in lens shape (more convex or concave) to focus light from objects at different distances in order to maintain a clear image
What is the cornea? Why is it avascular
- Transparent front part of the eye which covers the iris and the lens
- Refracts light to generate optical power
- Avascular so it is transparent
What is the iris?
-The coloured part of the eye which contracts and relaxes to adjust the amount of light reaching the lens
What is retinal detachment? Why can it occur?
- Trauma to the face can cause the retina to become detached from the eyeball causing flashes/blurring in unilateral vision.
- Can occur as the retina and choroid have different embryological origins-> initially separated by intraretinal space but enentually fuse together -> leaves weak area
Can retinal detachment always be fixed?
-There is a time sensitive window to fix it
Why is photophobia experienced in meningitis?
-Optic nerve is a brain tract (outpouching of brain) and thus is surrounded by meninges (pia, arachnoid and dura mater)
Describe the segments/chambers of the eye
- Eyeball split into anterior and posterior segments -> posterior segment is behind the lens
- Anterior segment separated further into anterior and posterior chambers -> divided by ciliary body
What is the function of the aqueous humor of the eye?
-Provide oxygen and nutrients to the cornea and lens as it is avascular
What produces the aqueous humor of the eye and how does it circulate?
- Produced by ciliary body to fill both the anterior and posterior chambers of the eye
- Flows out through trabecular meshwork in the anterior chamber of the eye
What is open angle glaucoma?
- Condition where the trabecular meshwork becomes blocked abd excess fluid accumulates between the cornea and the iris
- Increases intraorbital pressure causing compression of optic nerve
- Progressive painless vision loss
What is a cataract?
-Hardening and flattening of the lens producing a reduced ability to focus vision and a glare as light scatters across the lens
Name the muscles of the orbit and their nerve supply
- Superior oblique -> Trochlear nerve
- Lateral rectus -> abducens
- Inferior oblique, inferior/superior/medial rectus, levator palpabrae superioris -> Oculomotor
What happens in a trochlear nerve palsy?
-Patient unable to look down and in (lost superior oblique)
What happens if inferior oblique is damaged?
-Cannot look up and in
Where does the central retinal artery come from?
-Ophthalmic artery
Describe what happens in a central retinal artery occlusion
- Loss of blood supply to retinal of eye except for at macula as it receives its blood supply from choroid
- Retina looks pale everywhere except macula
Describe the venous drainage of the eye
Why is this clinically relevant?
- Central retinal vein -> Superior ophthalmic vein -> cavernous sinus
- Means eye infection can track to brain
What is papiloedema?
-Optic disk swelling caused by increased intracranial pressure which slows venous drainage from the eye -> usually bilateral
How does central retinal vein occlusion differ from central retinal artery occlusion?
- Slow painful loss of vision -> will be rapid in artery
- Several haemorrhages seen on eyeball rather than pale
Explain Lacrimal drainage
-Lacrimal gland -> lacrimal sac -> nasolacrimal duct -> inferior meatus
What is the purpose of the eyelid?
-Protect from injury, excessive light and dryness
Describe the conjunctiva
- Stratified columnar epithelium which covers inside of the eyelids and sclera which helps to lubricate the eye
- Palpebral layer covers eyelid
- bulbar layer covers sclera
What is a meibomian cyst?
-Painless swelling of eyelid due to infection in the tarsal gland
What is a sty?
- Infection of the cillary gland causing painful swelling of the eyelid
- Usually caused by staph
What muscle opens the eyelid?
-Levator Palpabrae Superioris
superior tarsal
Which muscle closes the eyes?
-Orbicularis oculi
