Ocular Anatomy 9 Sclera and Choroid Flashcards
What is the sclera? Where are its borders?
Tough, realtively avascular outer casing of the eye
Fuses posteriorly with dural sheaths of optic nerve
Anteriorly is directly continuous with the cornea
Where is the thickest and thinnest point of the sclera
Thickest (1mm) at posterior pole
Thins to 0.6mm at equator
Thinnes (0.3mm) at posterior to tendinous insertions of the recti
What structures pierce the sclera? Where?
Anterior ciliary arteries - at insertion of each rectus - 2 for every rectus except lateral rectus -1
Long and short ciliary nerves and vessels - next to optic nerve head
Vortex veins - 4mm posterior to equator -
Optic nerve
Where does the opti nerve perforate the sclera?
3mm medial and 1mm above the posteiror pole
Lamina cribrosa (area of perforation in sclera)
What are the layers of the sclera?
Episclera
Stroma Lamina fusca
What is the episclera of the sclera?
Consists of loose CT and has a rich blood supply from anterior ciliary arteries that lie deep to the conjunctival vessels
These blood vessels are not constricted by topical adrenaline but are constricted by topical phenylephrine.
It is connected to Tenon’s capsule, the fascial sheath of the eyeball
How is stromal collagen organised? What types?
Random organisation, not regular lattice, hence not transparent
Types I and III collagen
What is the lamina fusca
Contains melanocytes
Weak collagneous attachments to the overlying choroid
How do you differentiate between episcleritis and scleritis
Episclera vessels are typically constricted by topical phenylephrine where are scleral ones are not
What is the uveal tract?
Vascular pigmented layer that consists of the choroid, ciliary body and iris
Where does the choroid lie?
Between the RPE in the retina and the sclera
What is the function of the choroid?
Provides the posterior third of the retina with nutrients, carries a blood supply forward to the anteiror of the globe
Light trap and heat sink - high melanocyte content, pigmenation of the choroid is profound an serves as a light sink preventing unwanted rays being reflected back on to the retina
What are the parts of the choroid?
Vessel layer, capillary layer, Bruch’s membrane
Where is the choroid attached to the sclera?
Exit of the vortex veins and at the optic nerve head
What is the blood supply to the choroid?
Blood vessels and nerves supplying the choroid lie in the suprachoroidal space between the choroid and the sclera.
Two long posterior ciliary arteries and short posterior ciliary arteries, and the perforating anterior ciliary arteries perfuse the choroid
Choroidal capillaries are lined by a continuous layer of fenestrated endothelial cells and are found to be most dense at the macula (in CRAO, blood flow in these vessels can be seen as foveal cherry red spot)
Drains into the vortex veins which flow into the ophthalmic vein
