LENS

Question 1

LENS

Answer 1

• transparent biconvex structure

- attached to ciliary body by zonular fibres (suspensory ligament)

Question 2

LENS LOCATION

Answer 2

• behind iris + pupil

- in front of vitreous body

Question 3

TOTAL EYE DIOPTRIC POWER

Answer 3

58D

Question 4

LENS DIOPTRIC POWER

Answer 4

15D (can change)

Question 5

ACCOMMODATION

Answer 5

15-16D at birth
8D at 40
1-2D at 60

Question 6

ANTERIOR + POSTERIOR POLES

Answer 6

CENTRE POINTS ON ANT. + POST. SURFACES

Question 7

AXIS OF LENS

Answer 7

LINE JOINING POLES

Question 8

EQUATOR

Answer 8

MARGINAL CIRCUMFERENCE

Question 9

STRUCTURE OF LENS

Answer 9

• capsule
• epithelial layer
• stroma

Question 10

LENS CAPSULE

Answer 10

• elastic basal membrane
• envelopes the lens
• elastic nature allows accommodation

Question 11

LENS EPITHELIAL LAYER

Answer 11

• cuboidal cells below capsule on ant. surface

- at equator cells elongate + form columnar cells - transform into lens fibres

Question 12

WHERE IS MITOTIC ACTIVITY GREATEST IN LENS?

Answer 12

AT EQUATOR

Question 13

STROMA LENS

Answer 13

• made up of lens fibres
• makes up bulk of lens
• fibres form from epithelial cells in germinal zone (at equator)

Question 14

WHAT KEEPS LENS FIBRES IN PLACE?

Answer 14

BALL + SOCKET JOINTS

Question 15

LENS FIBRES FROM SAME LAYER JOIN AT?

Answer 15

SUTURES

Question 16

LENS ENERGY

Answer 16

70% - glucose metabolised by anaerobic pathways

30% - aerobic metabolism of lens epithelium

Question 17

ADVANTAGE OF LENS USING MOSTLY ANAEROBIC METABOLISM

Answer 17

not susceptible to oxygen starvation - must have glucose

Question 18

OSMOTIC CONTROL OF WATER LEVELS IN LENS ACHIEVED BY WHAT?

Answer 18

SODIUM PUMP

only at anterior surface of lens

Question 19

WHAT HAPPENS TO CENTRAL NUCLEUS AS LENS AGES?

Answer 19

• becomes sclerosed (stiff) + yellow
• refractive index goes up
• results in reduced visual acuity
• increased absorption of blue (short wavelength) light

Question 20

LENS CAPSULE THICKEST AT WHAT POINT

Answer 20

ANTERIOR + POSTERIOR SURFACES CLOSE TO THE EQUATOR

thinnest at posterior pole