Cornea & Lens Flashcards
Properties and function of cornea?
45D
Correct curvature-refract light
Avascular- transmit light
Measurements?
HVID- 11.7mm
Radius- 7.8mm
Thickness- 0.52mm central/ 0.67 peripheral
RI- 1.376
How many layers and names?
5
Epi
Anterior limiting lamina ( Bowman’s mem)
Stroma
Posterior limiting lamina (Descemets mem)
Endo
Function of epithelium?
-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
Repair of epi?
Repair itself- by adjacent cells
3hrs
Continually produced and replaced
Larger wounds=7days
A. L. L ?
Acellular
Any damage beyond this layer = infection and long to heal
Structure of stroma?
90%of cornea
Lamellea of collagen fibres parallel
Regular arrangement +short diameter = transparent cornea
Keratocytes synthesise collagen
Repair of stroma?
Permanent damage
Keratocytes activated- into fibroblasts
Scar tissue produced
Not reversible
Endothelium structure and fuction?
Single layer. Hexagonal
5 microns
Controls hydration levels in stroma
Stroma kept in relative dehydration= deturgescence
Active transport from ant chamber to stroma
Endo repair?
Endo cells not replaced :. Permanent loss of cells
Neighbouring cells migrate
Polymegathism( enlarged cells)
Polymorphism ( vairation in cell shape)
Control of corneal hydration
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
Gas supply and removal in cornea?
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)
Corneal innervation
Parasympathetic NS
Trigeminal Vth nerve
Characteristics of lens?
2 poles- anterior(facing iris ) and posterior( facing vit)
Biconvex
Equator
Ant=flat, Post= steep
AVascular
RI = Central( 1.42)/ Peri(1.38)
Function of lens?
Tranmits incident light
15-20D
30% refractive power of eye
Defence against UV
Development of lens?
@birth: smaller, spherical, thicker, AL shorter so more power needed
@puberty: flatter and thinner
@old: thicker again
Structure of lens?
Modified epi cells- neat arrangement/ tight packed
Intercellular Pro ( 60% of crystallins)
Anatomical zones
look at picture
Nucleus- embryonic fibres
Cortex- fibres produced after puberty, pushed towards nucleus with age so lens =denser
Lens sutures
Each lens fibre runs front to back in U shape and meet in middle
Anterior Y suture
Posterior Y suture (upside down Y)
Lens capsule?
Bag that holds lens
Made of elastic basement mem( type IV collagen)
Thicker anteriorly
Important in accom and cataract surgery
Attached to zonules
Accommodation?
Unaccom: distance vision
Power = 17D
Lens=thin and flat
Accom: near vision
Power=30D
Lens=steep and thick
Lens metabolism
Since avascular, aq supplies O2 and nutrients
Aging of lens
Nucleus increase and cortex decrease
Increased yellowing-physiological/ NOT CATARACT
Decreased light trans
Increased thickness
Reduced accom- presbyopia
Cataract types
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
