Ch 1-2 Corneal, scleral and conjuntiva: Anatomy & Phisiology

Question 1

Describe corneal dimensions

Answer 1

Horizontal 11-12mm Vertical 9-11 0.5 mm thick in the center, 0.7 mm thick in the periphery

Question 2

Name the corneal radius of curvature and power

Answer 2

7.5-8mm in the central 3mm, 40-44D power.

Question 3

Name the optical qualities of the cornea

Answer 3

1. Transparency 2. Smoothness 3. Refractive power 4. Contour

Question 4

Name the refractive index of: air, tear, cornea, aqueous

Answer 4

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

Question 5

Sensitive innervation of the corneal (name the nerve)

Answer 5

Ciliary nerves, ophthalmic branch of fifth craneal nerve.

Question 6

Where is the terminal plexus of the sensitive nerves of the cornea located?

Answer 6

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.

Question 7

Which artery provides for scleral irrigation?

Answer 7

None, its avascular…

Question 8

Although the cornea is mainly avascular, the limbus is vascularized. Which vessels provide this irrigation.

Answer 8

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)

Question 9

Where does corneal oxigen supply comes from

Answer 9

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)

Question 10

name the thickness and volume of tear film

Answer 10

7um & 6.5uL

Lipid: 0,1um

Aqueous: 7um

Mucin: 0.01-0.05um

Question 11

What is the thickness of corneal epithelium

Answer 11

50um, constant throughout the entire surface.

Question 12

Which keratins are expressed in the corneal tissue

Answer 12

keratin 5/14, which also is present in the skin

Keratin 3/12, which are specific of the corneal tissue

Question 13

Are antigen presenting cells present in the cornea?

Answer 13

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.

Question 14

Do superficial corneal cells have proliferative capacity?

Answer 14

No they are fully differentiated cells.

Question 15

Name the main two phisiopathological reasons for mucin-deficiency form of dry eye:

Answer 15

1- loss of superficial cell glucocalix

2- loss of goblet cells.

Question 16

How is the corneal epithelial basement membran composed?

Answer 16

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)

Question 17

How is the bowman´s layer composed?

Answer 17

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.

Question 18

What are the main components of corneal stroma?

Answer 18

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)

Question 19

describe the arrangement of corneal collagen fibers

Answer 19

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

Question 20

Collagen fiber diameter

Answer 20

22.5-35nm

Question 21

Collagen fiber spacing

Answer 21

41.4 nm

Question 22

how long does it take for the corneal stroma to experience complete turn over.

Answer 22

it is estimated to take about 2-3 years.

Question 23

which one is the most abundant GAG of the cornea?

Answer 23

Keratan Sulfate (65% of total GAG content)

Question 24

Which core proteins are associated to keratan sulfate to form proteoglycans in the cornea?

Answer 24

Lumican, keratocan & mimecan

Question 25

Describe the layers of the descemet membrane

Answer 25

1. A thin layer (0.3um) adajacent to the stroma (Dua`s)
2. An anterior banded zone (2-4um), layed down during the embrionic stage.
3. a thick posterior non banded zone (>4um).

Question 26

Can the descemet membrane regenerate after it has been lost (after the epithelium has re-covered the area)?

Answer 26

No. Endothelium can migrate to cover the defect,but the descemet membrane does not regenerate.

Question 27

What are the dimensions of an endothelial cell?

Answer 27

5um thick, 20um width

Question 28

What is the normal coefficent of variation of the normal endothelium, and how is named when the value is increased?

Answer 28

1. Normal CV is: 0.25
2. Above this number is called polimegatism

Question 29

What is the normal value for hexagonality in the normal cornea, and what term is used when it is above the normal value?

Answer 29

Norma hexagonality is 60-80%

An increase in this number is called plemorphism

Question 30

Which are the phases of corneal epithelium healing?

Answer 30

1. Migration
2. Proliferation
3. Differentiation

Question 31

Which corneal tissues are derived from the neural crest?

Answer 31

Keratocytes and stroma, scleral fibroblasts, endothelium and trabecuar meshwork.

Question 32

which nodes drain the conjuntiva´s lymph?

Answer 32

preauricular and submandibular lymph nodes.

Question 33

which nerves provide the conjuntival sensitivity?

Answer 33

supratroclear, lacrimal, supraorbital and infraorbital branches of V craneal nerve.