352 Week 7-12

Question 1

Name the condition where there is no lens present.

Answer 1

Aphakia

Question 2

List the functional roles of the lens.

Answer 2

Accommodation, UV absorption, transmit visible light, and barrier between anterior and vitreous chambers

Question 3

describe the nature of the lens relative to the refractive index. (include values)

Answer 3

relative index of lens highest (1.406) within the nucleus (denser) and decreases outwards at cortex (1.386)

Question 4

describe which week in does the lens start and finish forming.

Answer 4

starts forming: wk5. does not finish forming. continues to form throughout life.

Question 5

describe which week in does the lens start and finish forming.

Answer 5

starts forming: wk5. does not finish forming. continues to form throughout life.

Question 6

which layer does the lens originate from?

Answer 6

surface ectoderm (lens placode)

Question 7

what happens at the lens equator?

Answer 7

attachment of zonules - important for accommodation and hold the lens in place

Question 8

what difference in the lens structure occurs between positive and negative accommodation?

Answer 8

(+)ve = far to near, ciliary muscle contracts, ciliary ring narrows, zonules relax, lens steepens, parasympathetic.

(-)ve = opposite to positive.

Question 9

what is the role of the lens capsule

Answer 9

transparent elastic membrane that envelopes the entire lens. keeps structure

Question 10

what is the role of the lens capsule?

Answer 10

transparent elastic membrane that envelopes the entire lens.

Question 11

what is the shape of lens epithelium in central zone, germinal zone and transitional zone?

Answer 11

central zone: squamous in shape, elliptical nuclei in mount view.
germinal zone: more peripheral cells, smaller and more cuboidal. compact nuclei.
transitional zone: more columnar, assume pyramidal shape.

Question 12

what is the difference between soluble and insoluble lens proteins. include prevalence (% of overall)

Answer 12

soluble: found in cortex (80-90% of proteins).
insoluble: found in nucleus, <15% proteins.

Question 13

describe anisocoria

Answer 13

varying pupil size of more than 0.3mm.

Question 14

describe the characteristic of pupil response.

Answer 14

latency of 250-350ms with irregular oscillations. pupillary thresholds are similar to visual thresholds. Pupillary reactions suppressed by light adaptation, return with dark adaptation.

Question 15

describe the two characteristics of the blood vessels in the iris.

Answer 15

fenestrated, overlapping endothelial cells (zonular occludens).

sheath.