Cornea + Lens Flashcards
بسم الله الرحمن الرحيم وبه نستعين
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Mention functions of cornea
(نظرت إلي عينه فا(ربكته
RPCT
-Refractive power 40 diopete 2/3 refreactic power of eye why?
-Protection of inner delicate structures
-Curvature is regular for sharp image formation
-Transperant allowing light to pass
Refractive power of cornea 40 diopeter 2/3 refreactic power of eye why?
Due to its curvature .
RI=1.38 differece between it and air is the biggest
Cornea depends on oxidative phosphorylation
Cornea uses glucose. so how it get its oxygen ?
Show conral nutririon sources !
From diffusion from :
85% From lacrimal film
Aquous
Limbal capillaries
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Mention causes of corneal tranparency
SCA TCU
Stratified squamous non keratinized epitehleium
- Collagen fibrils in the substania propria has
uniform diameter +parallel fibers
-Avascular
-Unmyelinated nerve fibers
-Tears for Moistening prevnening dryness
-Corneal dehydration how ?
-Corneal dehydration how ?
Corneal dehydraion is imp for Transparency of cornea so what are factors inducing it ?
-Surface epithelia factors:
1-Na/K pump getting rid of Na and H20
2-Tight junctions between theses cells preventing edema
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Endothelial factos:
-Na/K pump
-Na/H exhanger
-Carbonic anhydrase enzyme how ?
Carbonic anhydrase and corneal dehydration ?
H + HCO3= H2CO3
H2CO3= H20 + CO2
H20 goest out by Na osmosis
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if excessive H2O found in cells ?
H20+CO2=H2CO3
H2CO3=H+HCO3
H goes out of cell
: loss of corneal transparency.
: prevents normal passage of light. ?
Corneal oapcity
Correction by corneal graft
Mention causes of Corneal opacity
BAC
-Bowman capsule injuried causing scarring
-Vitamin A deficiency? Decrasing tear spreading causing dryness
-Corneal vascularization
lens Structure:-
a) Capsule:
b) Epithelium:
…….the capsule ..postiotn
…………….the capsule.. function
Maintains lens …….
At the …….., the epithelium form the…….:
* Younger fibers constitute the lens …..
* Older fibers constitute the lens…….
¤ The lens is formed of: …….+.,,,,,,,,
Structure:
a) Capsule: ELASTIC
b) Epithelium:
.underthe capsule ..postiotn
secrets the capsule.. function
Maintains lens vitality
At theeequator , the epithelium form the lens fibers
* Younger fibers constitute the lenscortex
* Older fibers constitute the lens nucleus
¤ The lens is formed of: H20+H2O soluble crystalline proteins
Lens R.I. = ? why ?
1.4 due to crystalline proteins
Lens dioptric power: ?diopters (resting) & ?diopters (fully
accommodating)
20 resting
34 accommodated fully
Nutrition of the lens occurs through?
Aquos humor by diffusion
The …..surface of the lens is more convex that the
….surface.
- The center of the anterior surface is the anterior pole.
- The center of the posterior surface is the posterior pole.
- The line that connects the 2 poles = lens axis.
The .posterior …surface of the lens is more convex that the
.anterior …surface.
Mention functions of lens ?
1-Plays important role in accommodation
2-20dipopetric power =1/3 refreactive power of eye
Mention causes of lens tranparency
avascular
painless non innervated
Fibers unifolrmly packed and arranged with less extracellular space
Glutatione antioxidant+ reducing proteins
Na/K Pump + Ca pump for osmotic equilibrium
a degenerative condition in
which there is a partial or complete loss
of lens transparency.
Catarct
Mention causes of Catarct
1-Congenital
2-Senile old age
3-Secondary to ?
1-uv and x rays causing protein denaturation
2-DM
3- decreased glutathione ? causing ROS damaging membrane of lens entering H2O and ions causing opacity
treatd by surgical removal of lens
Define aquous humor
Clear watery fluid filling the ant and post chambers of eye
Aquous humor is formed By active secretion by the ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, lining
the ciliary processes.
Aquous humor is formed By active secretion by the ,,Non Pigmented Epithelium NPE ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, lining
the ciliary processes.
Describe mechanisms of secertion of aquous humor
Active secertion by non pigmented epithelium through ? Na/K pump getting rid of sodium causing water to follow it also
Carbonic anydrase in NPE forming HCO3 goes out with CL- And water follows by osmosis
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Passive secretion :
1- Osmosis following electrolytes Na Cl- HCO3
2-Diffusion
3-Filtration
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nutrients as Glucose aminoacids and Ascorbic acid by ? Active transpotr of Facilitated diffusion
Aqueous is continuously formed & reabsorbed at a rate…. ml/day
2
Mention methods of draiage of Aquous humor ?
1-Episcleral out flow from posteror cahmber to anteiror one through pupil then to iridocorneal angle to Fontana spaces to Schlemme canal to Episcleral veins
2-Uveoscleral outflow : absorbed by ciliary bodies vessels
OR! : pass sclera to periocular tissue to be absorbed
Mention functions of aquous huomr
mneo
1-Maintains IOP
2-Nutriention O2 to lens and cornea
3-Excretion : drainage of metabolites from surrounding tissues
4-One of the refractive media of the eye
The pressure produced by aqueous humor
Measurement: …………………
Normal Value: …………………….
It shows diurnal variations:
………….. value in the morning & ………….value in the evening.
IOP
Tonometer digital
12-20mm Hg
Highest -Lowest ( due to pupil diltatioan and constriction by symp and parasymp causing change in angle )
