Eye 1: Outer fibrous layer

Question 1

Outer Fibrous layer of the eye consists of

Answer 1

• Cornea: transparent anterior 1/6
• Sclera: Opaque posterior 5/6

Question 2

Enumerate layers of the cornea

Answer 2

5 Layers:
1. Non-keratinezed stratified squamous epithelium
2. Bowman’s membrane
3. Substantia propria
4. Descemet’s membrane
5. Endothelium

Question 3

Describe non-keratinized stratified squamous epithelium of cornea

Answer 3

• Basal layer: Cubical/columnar with straight basement membrane, showing mitosis
• Intermediate: polyhydral cells, unmyelinated nerve endings
• Top Layer: Squamous cells with apical microvilli to retain a protective tear film

Question 4

Describe Bowman’s membrane (anterior limiting) of cornea

Answer 4

• Straight
• Non-cellular
• Very thick
• formed of collagen fibrils

Question 5

Describe substantia propria of cornea

Answer 5

• Main thickness of cornea
• 60 layers of parallel collagen bundles with keratocytes
• Embedded in ground substance rich in Lumican (proteoglycan)

Question 6

Describe Descemet’s (posterior limiting) membrane

Answer 6

• Basement membrane of corneal endothelium
• Non cellular layer of interwoven collagen fibers

Question 7

Describe endothelium of cornea

Answer 7

• Single layer of simple squamous epithelium responsible for
  1. Maintainance of Descemet’s membrane
  2. Optimum state of corneal hydration, by contiuous pump of sodium ions

Question 8

Enumerate factors responsible for corneal transparency

Answer 8

• Avascular Cornea
• Non keratinized surface epithelium
• Unmyelinated nerve ending
• Regular arrangement of lamellae of substatia propria
• All parts of substatia propria have the same refractive index
• Minimal hydration of cornea

Question 9

Mechanism of LASIK surgeory

Answer 9

Changing of corneal curvature

Question 10

Injury of Bowman’s membrane results in

Answer 10

Corneal Opacity

Question 11

Reason why corneal transplantation is usually successful

Answer 11

Cornea is avascular

Question 12

Corneal ulceration is avoided by

Answer 12

Microvilli of Top layer of corneal epithelium keeping the cornea wet

Question 13

Arrangement of Collagen type 1 fibers in the sclera

Answer 13

Various directions with scattered fibroblasts and some elastic fibers

Question 14

Insertion of extraocular muscles

Answer 14

Anterior part of sclera

Question 15

Decribe the changes that occur at the corneo-scleral junction (Limbus)

Answer 15

1. Non-keratinized stratified squamous epithelium becomes stratified columnar epithelium with goblet cells = Conjuctiva, with the stem cells connected
2. Bowman’s membrane is replaced by Subconjuctival C.T
3. Collegen fibers go from regular to Irregular
4. formation of Canal of Schlem
5. Descmet’s membrane and endothelium are replaced with Trabecular meshwork
6. Existance of Microvasculature

Question 16

Enumerate Refractive media of the eye from outside to inside

Answer 16

1. Cornea
2. Aqueous Humour
3. Lens
4. Vitrous Humour (body)

Question 17

Vitrous body is made up of

Answer 17

• Mucoid CT made up of hyalocytes, which form Collagen type 4 and hyalurinate

Question 18

Function of vitrous body

Answer 18

support the lens anteriorly & retina posteriorly

Question 19

Describe lens capsule

Answer 19

Elsatic, thick, homogenous, made up of Collagen type 4 and proteoglycans , it covers the whole lens

Question 20

Describe subcapsular epithelium of the lens

Answer 20

• Cuboidal epithelium at the Anterior surface only
• at the equator, there are stem cells resposible for growth of the lens

Question 21

Describe the lens fibers

Answer 21

cells lost their nucleous and organelles, and are made up of proteins called Crystallines