Where does the retina end anteriorly?
At the Ora Serrata, just in front of the equator of the eye
Function of the Humours of the eye?
Aqueous humor maintains intraocular pressure
Vitreous Humor cushions the retina
Describe the passage of the Aqueous Humor?
- Produced in ciliary body
- Feeds into posterior chamber
- Passes into anterior chamber throught he pupil in front of the lens
- Passes out the angle of the anterior chamber through the trabecular meshwork
- Finally drains out Schlemm’s canal into the episcleral veins
What pathologies are visible in relation to the orbital fat?
Starvation/malnutrition - If the eyes look sunken it can mean the person is using up their orbital fat which is one of the last stores to go
Thyroid disease - Orbital fat hypertrophy -> Staring protruding eye appearance
What glands exist in the eyelid?
Sebaceous glands at the base of the eyelashes (blockage = external stye)
Meibomian Glands (in the tarsal plate) produce the oily layer of the tear film
What is the tarsal plate?
A layer of dense connective issue that gives the eyelid shape
What is conjunctiva?
A thin vascular membrane covering the inner surface of the eyelid and the sclera (but not a cornea)
Whats the reason for the conjunctiva not covering the cornea?
Its very vascular (and capillaries leak) so it would obstruct the transparent nature of the cornea
Where is the lacrimal gland and how is it innervated?
Lateral roof of the orbit
Parasympathetic fibres from the Facial Nerve
Where do the lacrimal ducts open into the orbit?
The superior conjuncitval fornix (reflection)
How do excess tears drain?
Through punctae on the medial side of each eyelid into the lacrimal sac (over lacrimal bones) and down the nasolacrimal duct into the Inf meatus
Explain the innervation of the intrinsic eye muscles
Ciliaris & Constrictor Pupillae = Parasympathetic fibres from Cr N III
Dilator Pupillae = Sympathetic fibres from a plexus around blood vessels
Where do the extraocular muscles originate?
Levator Palapebrae Superioris - Roof of orbit
Recti - Annular Fibrous (tendinous) ring
Sup Oblique - Lesser Wing of sphenoid
Inf Oblique - Medial orbital floor
What does the oculomotor nerve carry?
Mostly somatic motor innervation to the extraocular muscles. Some Parasympathetic (Autonomic Motor) fibres --> Synapse at ciliary ganglion --> Ciliaris/Constrictor Pupillae
What are the branches of the ophthalmic nerve to the orbit and what do they do?
Enters through Sup Orbital Fissure
- > Nasocilliary nerve
- > Lacrimal nerve
- > Frontal Nerve
Supplies general sensory info to most of the orbit
How is the maxillary nerve related to the orbit?
It supplies sensory information to the floor of the orbit and the eyelids.
It passes through the inferior orbital canal into the orbit and out the infraorbital foramen as the infraorbital nerve
How does the ophthalmic artery reach the orbit?
Through the optic foramen alongside the optic nerve
Remember its a branch of the ICA
What branch of the ophthalmic artery supplies the retina
Central Retinal Art
Travels within the optic nerve
Supplies inner retinal layers (remember outer layers are supplied by the choroid)
What arteries supply the choroid?
Short posterior ciliary arteries (branches of the ophthalmic)
What arteries supply the ciliary body and iris (and anterior choroid)?
Long Posterior Ciliary Arteries
Summary of ophthalmic artery and branches:
Branches from ICA and enters orbit via the Optic Foramen
1) Central Retinal Art –> Travels within optic nerve –> Inner Retinal layers
2) Posterior Ciliary Arteries:
short - Choroid
Long - Iris/ciliary body/ant choroid
3) Ant/Post Ethmoidal Arteries -> Nasal cavity/septum superiorly
4) Muscular Arteries
What can we see using an ophthalmoscope and how do we divide it up
The optic disc (a physiological blind spot) and coming off it the central retinal artery and vein
The fovea centralis
We divide the image into 4 quadrants with the intersection on the optic disc:
What veins drain the eye and to where?
Sup & Inf Ophthalmic veins drain to the cavernous sinus via the sup orbital fissure
What lines the intracranial venous sinuses?
Squamous epithelium (Endothelium)
What nerves sit in the walls of the cavernous sinus?
Cr N 3,4,5,6 (2 sits just behind it)
Also the ICA passes through the sinus