WEEK 6: Crystalline Lens

Question 1

Describe the location of the lens

Answer 1

Located in the posterior chamber of the eye, behind the Iris and in front of the vitreous chamber

Question 2

What is the function of the crystalline lens?

Answer 2

• Provide 1/4 of the refractive power of the eye - accommodation (change the refractive power of the eye to see up close) 15 - 20D. Helps focus light onto the retina - filter of ultravioilet light and light with a wavelength of between 300 - 400 nm -wall between the anterior and posterior chamber, and make a seperated anterior and posterior structures of the eye. -

Question 3

Implications of lens dysfunctions

Answer 3

• struggling with accommodation - Presbyopia -

Question 4

Describe the structure and different layers of the lens

Answer 4

• Lens Capsule - Anterior epithelium - Lens Fibres Cortex, Adult nucleus, Foetal nucleus and embryonic nucleus

Question 5

Explain epithelial cell differentiation and the process of lens fibre formation

Answer 5

Epithelial cell proliferation occurs in the germinative zone. Cells are cubiodal. Then they move to the transitional zone were they are on their way to becoming lens fibres, then they move pass the equator to elongate and become secondary lens fibre cells. Below the equator cells become columnar in shape and elongate anteriorly and posteriorly. Cells become arranged in meridional rows.

Question 6

Where are primary cell fibres formed?

Answer 6

Embryogenesis

Question 7

Understand the structures involved in accommodation

Answer 7

Ciliary muscles Radial fibres Zonules Crystalline lens Circular fibres

Question 8

Understand and describe the process of accommodation

Answer 8

The ciliary muscles contract Circular fibres contract - moving the ciliary body forward and inward Releases tension on zonules lens become more spherical - increase in dioptric power which allows for clear near vision

Question 9

What type of cataract is this?

Answer 9

Sclerosis Cataract - hardening and yellowing/browning (brunescene)

Question 10

What type of cataract is this?

Answer 10

Cortical: usually wedge shaped opacities. Can also have visible striations (loss of structure) in cortex

Question 11

What type of cataract is this?

Answer 11

Nuclear Sclerosis: hardening, clouding and yellowing (brunescene)

Question 12

What type of cataract is this?

Answer 12

Sub-capsular: usually posterior

Question 13

The crystalline lens provides:

about 1/2 the refractive power of the eye

about 3/4 of the refractive power of the eye

all the refractive power of the eye

about 1/4 the refractive power of the eye

Answer 13

about 1/4 the refractive power of the eye

Question 14

Which of the following terms does NOT describe the human crystalline lens?

anterior surface follows an elliptical curve

biconvex

vascularised

transparent

Answer 14

vascularised

Question 15

The youngest fibres in the human crystalline lens are located at:

the equator

the anterior pole

the embryonic nucelus

the fetal nucleus

Answer 15

the embryonic nucelus

Question 16

The diameter of the crystalline lens does not change from birth to adulthood. true or false

Answer 16

false

Question 17

A lens bow is located in the [A] of the human crystalline lens

Answer 17

crystalline lens cortex

cortex

lens cortex

Question 18

The anterior Y suture is an erect Y.

True

False

Answer 18

False

Question 19

The fibres in the crystalline lens behave as a:

gland

neuron

muscle

syncytium

Answer 19

syncytium

Question 20

The refractive index of the crystalline lens ranges from:

1. 21-1.40
2. 41-1.60
3. 38-1.41
4. 8-1.0

Answer 20

1.38-1.41

Question 21

What is the main purpose of catalase and glutathione peroxidase in the crystalline lens?

to counteract oxidative damage to the crystalline lens from circulating hydrogen peroxide in the aqueous humor

to provide rigidity to the crystalline lens fibre cell membranes

to facilitate relaxation of accommodation

to promote uptake of glucose by the crystalline lens for lens metabolism

Answer 21

to counteract oxidative damage to the crystalline lens from circulating hydrogen peroxide in the aqueous humor

Question 22

Crystalline lens zonule are also known as:

suspensory ligaments

circular fibres

outer lens capsule

bundles

Answer 22

suspensory ligaments

Question 23

When the lens is accommodating, the ____ of the ciliary muscle contract. When the lens is not accommodating, the ______ of the ciliary muscle contract.

Answer 23

circular fibres

radial fibres

Question 24

Which type of cataract is normally associated with yellowing of the oldest fibres in the lens?

Answer 24

nuclear sclerosis