The Orbit Flashcards
What bones form the orbit?
- Frontal
- Sphenoid
- Lacrimal
- Ethmoid
- Maxillary
- Zygomatic
What are the 3 holes in the orbit?
- Optic foramen
- Superior orbital fissure
- Inferior orbital fissure
What is the orbit closely related to?
Air sinuses
What walls of the orbit are particularly weak?
Medial and inferior walls
What makes the walls of the orbit susceptible to injury
The presence of the paranasal air sinuses and the thin bone which separates them from the orbit
What cushions the globe?
Orbital fat
What does the orbital fat do?
Supports the globe
What is the AP length of the eyeball?
~24mm
What is the AP length of the orbit?
~40mm
When would the eyeball have a protruding appearance?
If the orbital fat was hypertrophied such as in thyroid eye disease?
What may very sunken eyes indicate?
The person has been losing a lot of body weight as it is one of the last fat reserves to go
What is on the outside of the eyelids?
-Skin (typically with hair follicles and sebaceous glands)
What is on the inside of the eyelids?
Mucous membrane known as conjunctiva
What must the conjunctiva be able to do?
Be wet and secret fluid
What is always found with the eyelashes?
Sebaceous glands
What happens when the sebaceous glands get blocked?
They get inflamed and enlarged forming styes
What muscle elevates the superior eyelid?
Levator palpebrae superioris
What muscle lies just anterior to the LPS and is involved in closing the eye?
Orbicularis oculi
What innervates the orbicularis oculi?
Facial nerve
What plate is located in the eyelid?
Tarsal plate
What is the function of the tarsal plate?
To keep the shape and provide firmness to the eyelid
What glands are found within the tarsal plate?
Meibomian glands
Conjunctiva
Thin vascular membrane that covers the inner surface of the eyelids and loops back over the sclera
What does the conjunctiva not cover?
Cornea
Fornix
Area with an angle
Why would you not want conjunctiva over the cornea?
The conjunctiva is very vascular and blood vessels especially capillaries often leak which would decrease the amount and quality of light passing through the cornea
Conjunctivits
Inflammation of the conjunctiva
Where is the lacrimal gland situated?
In the orbit laterally
What innervates the lacrimal gland?
Parasympathetic innervation (pre-ganglionic) via the facial nerve
What does the lacrimal gland duct open into?
Conjunctival sac
What happens when you blink?
The eyelids spread tears evenly on the surface of the cornea
Where do tears drain through?
Punctae on the medial side of each eyelid
What does the punctae drain into?
Lacrimal sac
Where does the lacrimal sac sit?
Over the lacrimal bone
What does the lacrimal sac drain into?
Drains through the nasolacrimal duct into the inferior meatus of the nasal cavity
What happens to the lacrimal sac when the orbicularis oculi contracts?
It opens the lacrimal sac when it contracts which creates a negative pressure which sucks in the tears
What do intrinsic ocular muscles do?
Control pupil diameter and helps alter lens curvature to enable us to see near objects
What do extrinsic ocular muscles do??
Move the eye
What does the optic nerve carry?
Visual impulses from the eyeball
What does the optic nerve leave the orbit through?
Optic foramen
Where does the trochlear nerve arise from?
The dorsal part of the midbrain
What ocular muscle does the trochlear nerve supply?
The superior oblique
What ocular muscles does the oculomotor nerve supply?
- Inferior oblique
- Medial rectus
- Superior rectus
- Inferior rectus
- Levator palpebrae superioris
Where do the parasympathetic fibres carried by the oculomotor nerve synapse?
Ciliary ganglion in the orbit
What ocular muscle does the abducent nerve supply?
Lateral rectus
