Sclera

• What is the function of the sclera?

  What's it made of?

  Tough outer layer that maintains the shape of the eyeball and protects all the intraocular components.

  
  

  its made of collagen, so it's string and can provide structural support.
• What colour is the sclera in

  - normal?

  - elderly, and why?

  - children, and why?

  - white

  
  

  - as we get older, the white becomes 'yellow', due to lipid deposits (fat being deposited).

  
  

  - it's a 'bluish' colour in very young children because the sclera is very thin and hasn't fully finished developing. We see the underlying choroidal pigment showing through.
• thickness of limbus?

  thinnest part?

  thickest part?

  0.5mm - very similar to the cornea

  
  

  thinnest (0.3mm) is where we have the muscular insertions (where the muscles join)

  
  

  thickest (1-1.4mm) is posteriorly at the back, where the optic nerve joins.
• What is the tenon's capsule? (5)

  (Facial sheath)

  - thin membrane that surrounds the globe

  - provides support for the eyeball

  - separates the eyeball itself from the fat we get in the socket.

  - it covers the sclera round at the front of the eye

  - attached by connective tissues posteriorly.
• Why do we get fat in the socket, and how is this an advantage when it comes to real life scenarios (example)?

  We get fat in the socket because it provides cushioning and 'something' for the eye to move around in so it's not rubbing against the bone of the eye socket itself.

  
  

  When people get injuries or a disease, the eyeball has to be removed, in order for a false eye to be put in. To make it more natural, when the eyeball is taken out, the tenons capsule is left in place. This is because it's attached to the muscle so when the prosthetic eye is attached to it, it will enable to eye to move more naturally.
• what is the aqueous drainage channels?

  - canal of schlemm

  - collector channels

  canal of schlemm - it drains the aqueous from the anterior chamber and is a circular canal that goes all the way round the limbus.

  
  

  collector channels - little shoots from the canal of schlemm that take fluid and aqueous, and drains it into the oral blood supply. it drains the canal of schlemm.
• Anterior cilliary arteries and veins

  they go through the sclera and provide a blood supply for the sclera, conjuctiva and ciliary body.

  they come from muscular branches (all from the ophthalmic arteries), and they extend and go onwards through the sclera and provide the ciliary body and forms the major arterial circle of iris.

  
  

  veins do the same but out the sclera.
• Vortices veins?

  - how many

  - what do they do

  - what are they

  2-4

  take blood from the choroid (the choroid has really dens vascular supply), and leave just behind the equator.

  big veins
• long ciliary nerves and arteries? (4)

  - go into the sclera at posterior aspect

  - then they travel forward and extend.

  - supply choroid, sclera and ciliary body

  - form majority of arterial circle of iris.
• short ciliary nerves and arteries? (4)

  - go in at the back, close to the optic nerve head

  - don't reach forward or extend

  - supply choroid and sclera

  - forms another arterial circle of zinn.
• Lamina cribosa

  - what does it allow passage of?

  - location?

  - how and what does it supply?

  - how is it distinguished, and with what equipment?

  - Allows passage of: optic nerve, central retinal artery and vein

  
  

  - It is the fenestrated area of the sclera, near the posterior pole of the globe, where the optic nerve fibres exit the eye.

  
  

  - Blood vessels would go into the side of the optic nerve through the lamina cribosa to supply the retina and the optic nerve.

  
  

  - It's seen with an ophthalmoscope and has a large cup to disc ratio.
• Why is the lamina cribosa the weakest point of the sclera?

  Nerve fibres travel in bundles through sieve like holes (fenestrations). Weakest point due to the many holes being close together.
• Does the sclera have layers?

  the 'layout' of the sclera?

  what 2 cells does it contain and what are they?

  - No, sclera doesn't have 'real' layers, but is divided into 4

  
  

  - Its connective tissues are dense and irregular, and the collagen fibres are cross cross (which is why we don't have any transparency).

  
  

  - It contains sclerocytes (laying down collagen fibres of sclera), and melanocytes (pigmented cells further towards the bottom)>
• What are the 4 'layers'?

  - episclera (outermost): vascular so contains blood vessels. (When eye goes red, the blood vessels are inflamed).

  
  

  - Stroma: main body, quite dense.

  
  

  - Lamina fusca: pigmented area, contains melanocytes.

  
  

  - Endothelium layer: simple, squamous (innermost)
• Blood supply of the sclera?

  -blood supply limited since it's mostly avascular

  
  

  -contains no capillary beds, only a few small branches from the episclera and choroid, and branches of the long posterior ciliary arteries

  
  

  - supplied by the ciliary arteries.
• 3 layers of vessels that cover anterior sclera?

  - conjuctiva

  - superficial episclera

  - deep episclera
• Venous drainage of the sclera?

  - episcleral, intrascleral and deep scleral plexuses

  
  

  - drain into anterior ciliary veins
• Nerve supply of the sclera?

  - profuse sensory innervation

  what happens if we get inflammation (hurt, or no?)

  where do the nerves come from?

  If we get inflammation to the sclera, it can be very painful.

  
  

  The nerves are coming from the ophthalmic branches of the trigeminal nerve (CN V), and the ciliary nerve.
• Similarities and differences between episcleritis and scleritis.

  Similarities:

  - both are nodular (red confined to one area and localised inflammation).

  - both are diffuse (red across the whole surface).

  
  

  Differences:

  Episcleritis:

  - benign and common

  - uncomfortable but not painful

  - swelling (oedema) at tenon's capsule

  - redness is at the conjunctiva and superficial episclera vessels, brick red and moves over the sclera.

  
  

  Scleritis:

  - less common and sight threatening

  - painful

  - swelling (oedema) across entire stroma

  - redness is deep episclera vessels, blueish red and doesn't move over the sclera.
• Sclera discoloration

  The sclera can sometimes become blue to older patients and yellow to younger patients.

  
  

  Yellow - may be a sign of 'jaundice'. The eye and skin goes yellow because there is a build up of bilirubin in the conjunctiva and the skin. Bilirubin is part of the normal breakdown of haemoglobin found in the bile, and if it doesn't do that then the build up of it causes the yellow colour in the skin and eye.

  
  

  Blue - may be due to collagen disease. Sclera thinning shows the underlying choroid and there is a colour change across the whole sclera.