The lens

Question 1

Composition of the lens matrix?

Answer 1

35% protein

65% water

Question 2

before examining the lens what must always be done?

Answer 2

induction of mydriasis (atropine)

Question 3

what are the developmental abnormalities of the lens?

Answer 3

1. microphakia

2. Aphakia

Question 4

what is microphakia?

Answer 4

smaller lens, usually associated with other ocular malformations
(edges of the lens can be seen during examination + processes of cell body)

Question 5

what is Aphakia?

Answer 5

absence of lens

extremely rare inherited condition

Question 6

what is a cataract?

Answer 6

any focal or diffuse opacity in the lens capsule (more important than developmental abnormalities)

Question 7

how does the opacity in cataracts occur?

Answer 7

failure of:

• nutrition of lens
• metabolism of the proteins of the lens
• the osmotic balance of the lens

Question 8

aetiology of cataracts?

Answer 8

genetic 
associated (due to other ocular diseases)
traumatic 
nutritive 
infectious 
toxic (UV radiation)
metabolic

Question 9

classification of cataracts by maturity?

Answer 9

early
immature 
mature 
intumescent 
hyper mature 
morgagnian

Question 10

describe early developed cataracts?

Answer 10

there is early focal opacity with sight unaffected, tapetal reflection is present

Question 11

describe immature development of cataracts?

Answer 11

the opacity is more extensive than early cases, and most of the lens is involved in the pathological process. the transparency of the lens is reduced but not totally lost
vision is affected

Question 12

describe mature development of cataracts?

Answer 12

the lens is totally opaque, and therefore the eye is functionally blind. there is no tapetal reflection

Question 13

describe intumescent development of cataracts?

Answer 13

a swollen enlarged lens

Question 14

describe hyper mature development of cataracts?

Answer 14

begin to liquify owing to proteolysis (lens reabsorption)
this process usually begins in the cortex and spreads to the nucleus
(the nucleus may remain with a shrunken capsule around it)

Question 15

describe morgagnian development of cataracts?

Answer 15

nucleus may shrink to the bottom of the lens whose cortex has liquefied (hyper mature + resorbing)

Question 16

clinical signs of cataracts?

Answer 16

opacity
in early stages vision isn’t impaired
pupil dilation
greyish-whitish discolouration of the pupil
both eyes affected in mature cataract stages

Question 17

which species usually suffers more from bilateral cataracts?

Answer 17

Cats (less common in dogs)

Question 18

treatment of cataracts?

Answer 18

medical therapy doesn’t exist

only treatment is surgery

Question 19

aim of cataract surgery?

Answer 19

to prevent severe secondary changes and to improve the vision
cataract will lead to degeneration and secondary changes
- severe and painful uveitis
- secondary glaucoma
- dislocation of the lens

Question 20

list the methods of cataract surgery?

Answer 20

1. intracapsular lens extraction (ICE)
2. Extracapsular lens extraction (ECE)
3. Phacoemulsification (PHACO)
4. Phacoemulsification + intraocular lens implantation

Question 21

describe intracapsular lens extraction?

Answer 21

removal of the entire lens without opening to tearing the lens capsule
does not work well on animals due to connections with the lens capsule and vitreous body –> collapse of vitreous body into anterior chamber

Question 22

describe extra capsular lens extraction (ECE)?

Answer 22

a wide (180˚) incision is made in the limbus and the anterior lens capsule, nucleus and cortex are extracted manually followed by rigorous flushing to remove any remaining lens particles

small portion of posterior capsule left in position –> prevents vitreous body collapse

Question 22

describe extra capsular lens extraction (ECE)?

Answer 22

a wide (180˚) incision is made in the limbus and the anterior lens capsule, nucleus and cortex are extracted manually followed by rigorous flushing to remove any remaining lens particles

small portion of posterior capsule left in position –> prevents vitreous body collapse

Question 23

describe phacoemulsification (PHACO)?

Answer 23

ultrasound chopping/ fragmentation of the lens material and sucking of these fragments

Question 24

define subluxation/ luxation?

Answer 24

partial or complete displacement of the lens from the fossa hyaloidea due to rupture of the zonules

Question 25

what is the primary cause of subluxation/ lunation?

Answer 25

hereditary cause

Question 26

what are the secondary causes of subluxation/ lunation?

Answer 26

glaucoma
cataract
intraocular tumour
traumatic injuries

Question 27

describe subluxation?

Answer 27

all zonules must be ruptured

movement of the eye during subluxation will determine if result will be anterior or posterior

Question 28

what is anterior lens lunation-subluxation?

Answer 28

lens luxation with anterior displacement of the iris

endothelial damage causes corneal oedema where the lens capsule touches it

Question 29

what is posterior lens lunation - subluxation?

Answer 29

increased lens movement causes the vitreous touching the posterior lens to separate from deeper vitreous, allowing more movement of the lens - eventually the damages vitreous liquefies and is replaced by aqueous
subluxation -> luxation under the effect of gravity -> lens sinks ventrally

Question 30

what happens with complete liquefaction of vitreous body?

Answer 30

lens sediments at bottom of liquified vitreous body

Question 31

treatment of anterior lens lunation-subluxation?

Answer 31

if high IOP:

• ICE intracapsular lens extraction
• PHACO + sulcus implanted IOL

Question 32

treatment of posterior lens luxation-subluxation?

Answer 32

medication (miotics, anti-inflammatory drugs)

surgery is contraindicated (do not remove lens from deep portion of the eye)