ANATOMY - Lens

Question 1

Where is the lens located?

Answer 1

In a saucer shaped space in the patellar fossa

Question 2

What is the hyalodo-capsular ligament (Weiger’s ligament)

Answer 2

Connects the posterior pole of the lens to the patellar fossa

Question 3

What is retrolental space? (Berger’s space)

Answer 3

Space which exists between hyaloid face and lens within circular ligament

Question 4

What is the function of the lens? (3)

Answer 4

1) Transmits and refracts light - 35% refractive power

2) Lens absorbs UVA light < 350nm wavelength

3) It helps in accomodation

Question 5

What is the radius of curvature of the anterior surface of the lens vs posterior surface of lens

Answer 5

Posterior surface is more curved and thinner , so it is 6mm vs 10mm anterior surface (thicker)

Question 6

What is the equatorial diameter of the lens at birth vs adulthood

Answer 6

6.5mm at birth, 9-10mm in adulthood

Question 8

What is the lens thickness at birth and at extreme adulthood (what is average rate of growth)

Answer 8

3.5mm at birth, 5.5mm extreme adult life (0.2mm each year)

Question 8

How far is the anterior pole of the lens from the centre of the cornea?

Answer 8

3mm from the cornea

Question 8

What is the refractive index of the lens? What is the refractive power of the lens?

Answer 8

index - 1.39
power - 16-17D

Question 9

What material is contained within the lens capsule?

Answer 9

hyaline collagenous membrane that surrounds lens, elastic but contains no elastic fibres

Question 10

What is the structure of the anterior lens epithelium?

Answer 10

Cubiodal nucleated epithelium

Question 11

What is the epithelium in the equatorial region of the lens?

Answer 11

columnar cells –> they actively divide

Question 12

What is the difference in shape between the central, peripheral and equatorial epithelial cells

Answer 12

central: cuboidal
peripheral: smaller and cynlindrical
equatorial: columnar

Question 13

Which lens epithelial cells undergo mitosis? central? peripheral? equatorial?

Answer 13

central epithelial cells: undergo metaplasia in shield cataract –> glaucomfleken

peripheral zone epithelial cells: rarely undero mitosis

equatorial zone: actively mitose, and migrate posteriorly to form new lens fibres –> dysplasia of these cells called posterior subcapsular cataract (myotonic dystrophy, radiation, neurofibromatosis

Question 14

What are the causes of posterior subcapsular cataract?

Answer 14

myotonic dystrophy, radiation, neurofibromatosis

Question 15

What is the bow region of the lens?

Answer 15

The newly laid lens fibres from migratory cells of equatorial zone ELONGATE so that their nuclei are more anterior to the nuclei of the older, more superficial cells

Question 16

What is the difference between Elschnig’s pearls and Soemmering’s rings?

Answer 16

POSTERIOR CAPSULAR OPACIFICATION: Residual epithelial cells migrate posteriorly and differentiate into a balloon like wedl cell –> Elschnig pearl

If become a doughnut shape configuration - Soemmering’s rings.

Question 17

What is the structure of the nuclear zone lens fibres? Where do they develop from?

Answer 17

Primary lens fibres : develop from posterior epithelium before 3 months of age (oldest cells are in the centre)

Secondary lens fibres: develop from the equatorial zone (youngest cells are in the periphery)

Question 18

Whats the difference between anterior and posterior Y sutures in the lens?

Answer 18

Anterior: upright erect Y
Posterior: offset inverted Y

Question 19

What are the different zones in the lens? What ages are they?

Answer 19

see picture

Question 20

What is the lens capsule produced by?

Answer 20

Basal portion of lens epithelium anteriorly, basal portion of posterior lens fibres posteriorly

Question 21

Where do the zonules of zinn arise from and where do they insert?

Answer 21

Arise from the posterior end pars plana of ciliary body (up to 1.5mm from ora serrata) and insert into the equator of the lens

Question 22

Whats the difference between phacolytic glaucoma and phacoanalytic glaucoma and phacomorphic and lens particle glaucoma?

Answer 22

Phacolytic: lens proteins leaking through intact capsule to anterior chamber in hypermature cataract and with engorged macrophages which block trabecular meshwork

Phacoanaphylactic: autoimmune granulomatous reaction to exposed lens proteins in eye following trauma or surgery (after fracture of capsule) due to trabeculitis or blockage of TM by inflammatory cells

Phacomorphic: secondary angle closure due to enlargment of cataract lens causing pupillary block

Lens particle: Acute obstruction of TM by fragments of lens material

Question 23

What is the pathophysiology process behind cataract?

Answer 23

Break down of lens crystallins to albuminoids.

RF: Hypocalcaemia, diabetes, ionizing radiation and mechanical trauma

Question 24

What is the basement membrane of the lens capsule composed of?

Answer 24

Elastic basement membrane rich in type IV collagen and sulphated GAGs

Question 25

Which is the most important antioxidant molecule of the lens?

Answer 25

Reduced glutathione

Ascorbic acid metabolites can induce a cataract.

Question 26

Where does snowflake cataract occur and which patient cohort does it happen in?

Answer 26

Appears in lens cortex - occurs in type 1 diabetes

Question 27

What metabolic disturbances can cause cataract? (3)

Answer 27

1. Defects in galactose metabolism
2. Deficiency in galactose kinase
3. In diabetes mellitus

Question 28

What is the major component of the lens capsule and zonules to help with elastic properties?

Answer 28

Fibrillin