Ch 1-2 Corneal, scleral and conjuntiva: Anatomy & Phisiology Flashcards
Describe corneal dimensions
Horizontal 11-12mm Vertical 9-11 0.5 mm thick in the center, 0.7 mm thick in the periphery
Name the corneal radius of curvature and power
7.5-8mm in the central 3mm, 40-44D power.
Name the optical qualities of the cornea
- Transparency 2. Smoothness 3. Refractive power 4. Contour
Name the refractive index of: air, tear, cornea, aqueous
Air: 1.000
Tear: 1.336
Cornea: 1.376* (real)
aqueous: 1.336
*Keratometers take into consideration the changes induced by the posterior corneal surface by using a keratometric index of 1.3375
Sensitive innervation of the corneal (name the nerve)
Ciliary nerves, ophthalmic branch of fifth craneal nerve.
Where is the terminal plexus of the sensitive nerves of the cornea located?
It is located right at the winged cell layer of the cornea.
Which means that the loss of the most superficial cell layer would leave them exposed.
Which artery provides for scleral irrigation?
None, its avascular…
Although the cornea is mainly avascular, the limbus is vascularized. Which vessels provide this irrigation.
Anterior ciliary arteries, Which come from the ophthalmic artery, and anastomose with branches form de facial artery (which means that the cornea is supplied from both the internal and external carotid)
Where does corneal oxigen supply comes from
90% comes from the tear film, 10% from the aqueous.
(this means that the eye needs air exposure, if this is impeded corneal metabolism switches to anaerobic i.e: sleep)
name the thickness and volume of tear film
7um & 6.5uL
Lipid: 0,1um
Aqueous: 7um
Mucin: 0.01-0.05um
What is the thickness of corneal epithelium
50um, constant throughout the entire surface.
Which keratins are expressed in the corneal tissue
keratin 5/14, which also is present in the skin
Keratin 3/12, which are specific of the corneal tissue
Are antigen presenting cells present in the cornea?
Yes, Langerhans cells are present under normal conditions in the peripheral cornea, which is why corneal transplants should be performed away from the limbus to prevent transplant rejection.
Do superficial corneal cells have proliferative capacity?
No they are fully differentiated cells.
Name the main two phisiopathological reasons for mucin-deficiency form of dry eye:
1- loss of superficial cell glucocalix
2- loss of goblet cells.
How is the corneal epithelial basement membran composed?
An external lamina lucida, and a depper electron-dense layer.
Main structural components are laminin and type IV collagen (specifically alfa-5)
Alfa-2 (IV) collagen is present in conjuntiva and amniotic membrane (the functional difference is unknown)
How is the bowman´s layer composed?
12um thick layer of randomly arranged collagen (mainly type I & III) which are barely smaller in diameter than the ones that are present in the stroma.
What are the main components of corneal stroma?
keratocites are the main cell, but accounting only for 2-3% of total volume.
collagen contributes to aprox 70% of corneal dry weight. (mainly type I, but also III, V and VI)
describe the arrangement of corneal collagen fibers
homogenous, orthogonal.
spacing is less than half of that of visible light (400-700nm
) phenomenon that is thought to explain why scattered light by one fiber in the cornea is cancel by that from other scattered rays, allowing for transparency
Collagen fiber diameter
22.5-35nm
Collagen fiber spacing
41.4 nm
how long does it take for the corneal stroma to experience complete turn over.
it is estimated to take about 2-3 years.
which one is the most abundant GAG of the cornea?
Keratan Sulfate (65% of total GAG content)
Which core proteins are associated to keratan sulfate to form proteoglycans in the cornea?
Lumican, keratocan & mimecan
Describe the layers of the descemet membrane
- A thin layer (0.3um) adajacent to the stroma (Dua`s)
- An anterior banded zone (2-4um), layed down during the embrionic stage.
- a thick posterior non banded zone (>4um).
Can the descemet membrane regenerate after it has been lost (after the epithelium has re-covered the area)?
No. Endothelium can migrate to cover the defect,but the descemet membrane does not regenerate.
What are the dimensions of an endothelial cell?
5um thick, 20um width
What is the normal coefficent of variation of the normal endothelium, and how is named when the value is increased?
- Normal CV is: 0.25
- Above this number is called polimegatism
What is the normal value for hexagonality in the normal cornea, and what term is used when it is above the normal value?
Norma hexagonality is 60-80%
An increase in this number is called plemorphism
Which are the phases of corneal epithelium healing?
- Migration
- Proliferation
- Differentiation
Which corneal tissues are derived from the neural crest?
Keratocytes and stroma, scleral fibroblasts, endothelium and trabecuar meshwork.
which nodes drain the conjuntiva´s lymph?
preauricular and submandibular lymph nodes.
which nerves provide the conjuntival sensitivity?
supratroclear, lacrimal, supraorbital and infraorbital branches of V craneal nerve.
