Crystalline Lens

Question 1

what is the crystalline lens

Answer 1

all cells, transparent, biconvex structure

Question 2

what is the posterior curvature

Answer 2

5-8mm radius of curvature

Question 3

what is the anterior curvature

Answer 3

8-14mm

Question 4

which side, anterior or posterior of the lens is steeper

Answer 4

the posterior side

Question 5

how far away from the pars plicata is the lens equator

Answer 5

about 0.5mm away from the ciliary processes

Question 6

what are the dimensions of an adult lens (unaccommodated)

Answer 6

10mm in diameter and 4mm thick

Question 7

what changes as we age, the diameter or thickness of the lens

Answer 7

the thickness, increases about 0.02mm per year

Question 8

what keeps the lens in place on the posterior surface to the anterior surface of the vitreous

Answer 8

the hyaloid capsular ligament

Question 9

how much of the total power of the eye is the lens power

Answer 9

about 15 to 20 D (the cornea accounts for the rest)

Question 10

what are the 3 parts to the lens

Answer 10

an elastic capsule, lens epithelium, and lens fibers

Question 11

what is the thickest basement in the body

Answer 11

the elastic capsule of the lens

Question 12

where is the thickest part of the lens

Answer 12

just anterior and posterior to the equator

Question 13

where is the lens the thinest

Answer 13

at the posterior pole

Question 14

does the posterior side have an epithelium

Answer 14

no

Question 15

how is the lens capsule secreted anteriorly

Answer 15

by the anterior lens epithelium

Question 16

how is the lens capsule secreted posteriorly

Answer 16

by the superficial lens fibers

Question 17

which side of the lens capsule thickens with age, posterior or anterior

Answer 17

the anterior side does

Question 18

what are the two functions of the lens capsule

Answer 18

act as a diffusion barrier that is freely permeable to low-molecular weight compounds and to make the lens more pliable in response to the pull of the zonular fibers during accommodation

Question 19

where do the zonules attach to the lens capsule

Answer 19

between the equator and the poles

Question 20

why is there no posterior epihelium

Answer 20

it was used to form the primary lens fibers during embryonic development

Question 21

where do cells proliferate

Answer 21

the pre-equatorial (germanative zone) near the equator

Question 22

what happens to the cell after it is created

Answer 22

it transitions into an elongated columnar shape and arranged in meridional rows and will become secondary lens fibers

Question 23

do any of the fibers die off as we age

Answer 23

no, they become compacted and make the lens less pliable

Question 24

how does the lens receive nutrients

Answer 24

the central anterior epithelium is involved in the transport of substances from the aqueous humor (the lens is avascular)

Question 25

what is the bulk of the lens

Answer 25

the secondary fibers

Question 26

where is the nucleus located in the secondary lens fibers

Answer 26

it is anterior, it gradually disintergrates and the fiber will lose contact with the basement membrane

Question 27

what are lens Y sutrures

Answer 27

the place where anterior and posterior end of fibers meet

Question 28

how long and what shape are the lens fibers

Answer 28

they are 10mm long and U-shaped to fit in the lens (4-5mm thick)

Question 29

which side, anterior or posterior is the Y suture upright

Answer 29

the anterior side

Question 30

how are the lens fibers held together

Answer 30

by interlocking adjacent plasma membranes (ball and socket)

Question 31

what type of junction is present in the fibers

Answer 31

gap junctions to permit the deeper fibers with nutrients from the aqueous humor

Question 32

besides suppling nutrition what else to the gap junctions aid with

Answer 32

helping the lens to act like a single cell

Question 33

what is the epithelium-fiber interface

Answer 33

the border of the apical portion of the anterior epithelium and the apical portion of the secondary lens fiber

Question 34

after the nuecli are lost in the fibers, what happens to them

Answer 34

they become specialized to form crystallins (alpha and beta): the bulk of the lens fiber 40%

Question 35

why is the lens so refractive

Answer 35

due to the specialization of the fibers forming crystallins

Question 36

what is the earliest fiber mass called

Answer 36

the embryonic nucleus (center of lens)

Question 37

when is the embryonic nucleus formed

Answer 37

first 2 months of embryonic development (doesn't increase in size)

Question 38

what fibers are formed before birth that have the Y sutures

Answer 38

the fetal nucleus

Question 39

what nucleus has the fibers formed between birth and sexual maturation, that increases throughout life

Answer 39

the adult nucleus

Question 40

is there blood supply to the crystalline lens

Answer 40

not after embryologic development