Lente/Refractive

Question 1

Capsule anatomy

Answer 1

Basement membrane made of type IV collagen

Thickest anteriorly and at posterior prequatorial zones

Question 2

Zonules!

Answer 2

Insert 1.5 mm anterior to equator and 1.25 mm posterior to equator

Eosinophilic

PAS positive

Question 3

Lens proteins

Answer 3

Water soluable

1. Alpha , largest , heat shock
2. Beta
3. Gamma , don’t associate

Water insoluble :
Urea soulable - vimentin and phakinin and filensen
Urea insoluble - major intrinsic protein is an aquaporin

Aging causes increase in water insoluble fraction

66% water/ 33% protein

Question 4

Lens Energy

Answer 4

Anaerobic glycolysis limited by phosphofructokinase

HMP Shunt - less than 5% of metabolism

Sorbitol pathway - Aldose reductase ; only if too much sugar around , driven by high NAPDH/ NADH ratio

Glutathione is the free radicals scavenger

Question 5

Embryology

Answer 5

25 days of gestation: 2 lateral evaginations, optic vesicles from forebrain

27 days: ectoderm cells over vesicles become columnar needs BMP

29 days: infolding of lens placode

8 weeks: y sutures

3 months: zonules

Question 6

Gene for age related cortical cataracts

Answer 6

EPHA2

Question 7

Amiodarone

Answer 7

Stellar pigment deposition in anterior cortical axis

Also verticillata and rare optic neuropathy

Question 8

Statin

Answer 8

+ erythromycin can increase risk of cataract

Question 9

Prolate

Answer 9

Steeper centrally and progressively flattens to periphery

Flatter nasally than temporally

Question 10

How to measure wavefront aberration

Answer 10

Hartmann shack: shapes
Zernike: mathematical formulas represented by root mean square (higher = more abberation)
Fourier analysis: sine wave derived transformation of a complex shape

Question 11

Lower order aberrations

Answer 11

Zero: piston
First: vertical and horizontal prism
Second: myopia, hyperopia and regular astigmatism

Question 12

Higher Order Aberrations

Answer 12

Spherical: peripheral light rays focus in front of central rays = halos

Coma (third order): rays at one edge of pupil focus before rays at the other edge do - commonly caused by decentered things

Trefoil (third order)

Question 13

Asphericity

Answer 13

Q value
Zero for spherical corneas
Negative if prolate
Positive if oblate

Normally: - 0.26

(Myopic lasik makes the cornea more oblate)

Question 14

Piggyback IOLs

Answer 14

Combined power needs to increased by +1.50 or +2.00

Use two different materials

Question 15

Hemholtz hypothesis

Answer 15

Distance - ciliary muscle is relaxed and zonular fibers on tension

Accommodation : tension on zonules released, decreased equatorial lens diameter and increased curvature of anterior and posterior lens surfaces