Cornea + Lens

Question 1

بسم الله الرحمن الرحيم وبه نستعين
__________________________
Mention functions of cornea

Answer 1

(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

Question 2

Refractive power of cornea 40 diopeter 2/3 refreactic power of eye why?

Answer 2

Due to its curvature .
RI=1.38 differece between it and air is the biggest

Question 3

 Cornea depends on oxidative phosphorylation
 Cornea uses glucose. so how it get its oxygen ?
Show conral nutririon sources !

Answer 3

From diffusion from :
85% From lacrimal film
Aquous
Limbal capillaries
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Question 4

Mention causes of corneal tranparency

Answer 4

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 ?

Question 5

-Corneal dehydration how ?
Corneal dehydraion is imp for Transparency of cornea so what are factors inducing it ?

Answer 5

-Surface epithelia factors:
1-Na/K pump getting rid of Na and H20
2-Tight junctions between theses cells preventing edema
________________________________
Endothelial factos:
-Na/K pump
-Na/H exhanger
-Carbonic anhydrase enzyme how ?

Question 6

Carbonic anhydrase and corneal dehydration ?

Answer 6

H + HCO3= H2CO3
H2CO3= H20 + CO2
H20 goest out by Na osmosis
___________________-
if excessive H2O found in cells ?
H20+CO2=H2CO3
H2CO3=H+HCO3
H goes out of cell

Question 7

: loss of corneal transparency.
: prevents normal passage of light. ?

Answer 7

Corneal oapcity
Correction by corneal graft

Question 8

Mention causes of Corneal opacity

Answer 8

BAC
-Bowman capsule injuried causing scarring
-Vitamin A deficiency? Decrasing tear spreading causing dryness
-Corneal vascularization

Question 9

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: …….+.,,,,,,,,

Answer 9

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

Question 10

Lens R.I. = ? why ?

Answer 10

1.4 due to crystalline proteins

Question 11

Lens dioptric power: ?diopters (resting) & ?diopters (fully
accommodating)

Answer 11

20 resting
34 accommodated fully

Question 12

Nutrition of the lens occurs through?

Answer 12

Aquos humor by diffusion

Question 13

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.

Answer 13

The .posterior …surface of the lens is more convex that the
.anterior …surface.

Question 14

Mention functions of lens ?

Answer 14

1-Plays important role in accommodation
2-20dipopetric power =1/3 refreactive power of eye

Question 15

Mention causes of lens tranparency

Answer 15

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

Question 16

a degenerative condition in
which there is a partial or complete loss
of lens transparency.

Answer 16

Catarct

Question 17

Mention causes of Catarct

Answer 17

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

Question 18

Define aquous humor

Answer 18

Clear watery fluid filling the ant and post chambers of eye

Question 19

Aquous humor is formed By active secretion by the ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, lining
the ciliary processes.

Answer 19

Aquous humor is formed By active secretion by the ,,Non Pigmented Epithelium NPE ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, lining
the ciliary processes.

Question 20

Describe mechanisms of secertion of aquous humor

Answer 20

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

Question 21

Aqueous is continuously formed & reabsorbed at a rate…. ml/day

Answer 21

2

Question 22

Mention methods of draiage of Aquous humor ?

Answer 22

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

Question 23

Mention functions of aquous huomr

Answer 23

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

Question 24

The pressure produced by aqueous humor
Measurement: …………………
 Normal Value: …………………….
It shows diurnal variations:
………….. value in the morning & ………….value in the evening.

Answer 24

IOP
Tonometer digital
12-20mm Hg
Highest -Lowest ( due to pupil diltatioan and constriction by symp and parasymp causing change in angle )

Question 25

 Regulation: of IOP ? mainly by …………………..
Normally, if IOP  slightly Increased ?

Answer 25

oUT FLOW OF AQUOUS
____________________
distension of spaces of Fontana  
the rate of drainage  return of IOP back to normal.

Question 26

Mention functions of the IOP ?

Answer 26

MaintainS spheroid shape of the eye
and
Maintaind eye in resting condition flattened lens how ?
Flattening force :Compressing the lens anterior surface causing its flatenning
also ?
Stretching force on suspensory ligaments helps in flattening

Question 27

Glaucoma
 Definition: it is the increase of IOP above ? mmHg

Answer 27

20

Question 28

Mention causes of glucaoma?

Answer 28

Due to increased IOP above 20 mmHg
due to
Increased formation of aquous humor (rare)
also
decreased Drainage :
OPen angle gluacoma the angle it intact but the Trabeculart meshwork is obsrtucted
CLosed angle glaucoma: the angle is obstructed may be an inflammatory adhesions

Question 29

Mention effects of Gluacoma

Answer 29

1-pressure on the painful structrues of eye causing headache
2-pressure on the lens causing loss of accommodation with near vision
3-pressure on the Optic nerve+ retinal artery

Question 30

Mention Tratment methods of Gluacoma

Answer 30

1-Carbonic anydrase inhibitor diamox acetazolamide for decreasing HCO3 and H20 osmosis so remove 1/4 secertion of Aquous 1
2- Pupilloconstrictor pilocarpine for dilating the angle irdiocorneal angle
3- Surgical opening of the trabeular meshwork to increased outflow of aquous

Question 31

الحمدلله رب العالمين