Cornea & Lens

Question 1

Properties and function of cornea?

Answer 1

45D
Correct curvature-refract light
Avascular- transmit light

Question 2

Measurements?

Answer 2

HVID- 11.7mm
Radius- 7.8mm
Thickness- 0.52mm central/ 0.67 peripheral
RI- 1.376

Question 3

How many layers and names?

Answer 3

5
Epi
Anterior limiting lamina ( Bowman’s mem)
Stroma
Posterior limiting lamina (Descemets mem)
Endo

Question 4

Function of epithelium?

Answer 4

-Contains microvilli and microplicae to increase SA
-adhesion of tear film mucins to cornea
-prevent pathogen penetration into eye
-reduce friction during blinking
-maintain hydrophilicity of surface

Question 5

Repair of epi?

Answer 5

Repair itself- by adjacent cells
3hrs
Continually produced and replaced
Larger wounds=7days

Question 6

A. L. L ?

Answer 6

Acellular
Any damage beyond this layer = infection and long to heal

Question 7

Structure of stroma?

Answer 7

90%of cornea
Lamellea of collagen fibres parallel
Regular arrangement +short diameter = transparent cornea
Keratocytes synthesise collagen

Question 8

Repair of stroma?

Answer 8

Permanent damage
Keratocytes activated- into fibroblasts
Scar tissue produced
Not reversible

Question 9

Endothelium structure and fuction?

Answer 9

Single layer. Hexagonal
5 microns
Controls hydration levels in stroma
Stroma kept in relative dehydration= deturgescence
Active transport from ant chamber to stroma

Question 10

Endo repair?

Answer 10

Endo cells not replaced :. Permanent loss of cells
Neighbouring cells migrate
Polymegathism( enlarged cells)
Polymorphism ( vairation in cell shape)

Question 11

Control of corneal hydration

Answer 11

Done by endo- tight junctions
Limit access of H2O from aq to stroma bz fluid btwn coll fibrils =disruption of arrangement=loss of tranparency
AT of fluid from stroma to aq
AT of nutrients from aq to stroma

Question 12

Gas supply and removal in cornea?

Answer 12

O2 from: atmosphere, limbal cap, palpebral cap, aq
** O2 availability from air not available when eye closed
CO2 removal: cornea to tear film(open eye)
Thru aq (closed eye)

Question 13

Corneal innervation

Answer 13

Parasympathetic NS
Trigeminal Vth nerve

Question 14

Characteristics of lens?

Answer 14

2 poles- anterior(facing iris ) and posterior( facing vit)
Biconvex
Equator
Ant=flat, Post= steep
AVascular
RI = Central( 1.42)/ Peri(1.38)

Question 15

Function of lens?

Answer 15

Tranmits incident light
15-20D
30% refractive power of eye
Defence against UV

Question 16

Development of lens?

Answer 16

@birth: smaller, spherical, thicker, AL shorter so more power needed
@puberty: flatter and thinner
@old: thicker again

Question 17

Structure of lens?

Answer 17

Modified epi cells- neat arrangement/ tight packed
Intercellular Pro ( 60% of crystallins)

Question 18

Anatomical zones

Answer 18

look at picture
Nucleus- embryonic fibres
Cortex- fibres produced after puberty, pushed towards nucleus with age so lens =denser

Question 19

Lens sutures

Answer 19

Each lens fibre runs front to back in U shape and meet in middle
Anterior Y suture
Posterior Y suture (upside down Y)

Question 20

Lens capsule?

Answer 20

Bag that holds lens
Made of elastic basement mem( type IV collagen)
Thicker anteriorly
Important in accom and cataract surgery
Attached to zonules

Question 21

Accommodation?

Answer 21

Unaccom: distance vision
Power = 17D
Lens=thin and flat
Accom: near vision
Power=30D
Lens=steep and thick

Question 22

Lens metabolism

Answer 22

Since avascular, aq supplies O2 and nutrients

Question 23

Aging of lens

Answer 23

Nucleus increase and cortex decrease
Increased yellowing-physiological/ NOT CATARACT
Decreased light trans
Increased thickness
Reduced accom- presbyopia

Question 24

Cataract types

Answer 24

Named after area of lens:
Nuclear - seen with SL optic section
Cortical-Sl retro ill or direct ophthalmoscope
Posterior sub capsular- retro ill or direct opthamolscope
Anterior/Posterior polar

Question 25

Causes of catarct

Answer 25

Oxidative damage to proteins
Disruption of lens fibres due to
-age
-disease
- meds
- metabolic stress
-radiation
-trauma