Optics

Question 1

Prentice’s Rule

Answer 1

Prismatic power of lens is:

Delta = hD, where h is distance from optical axis in cm (not mm) and D is power of lens

Question 2

Prismatic effect of glasses on deviations

Answer 2

2.5 x D = % difference

Minus measures more
Plus measures less

Question 3

Basic lens formula

Answer 3

U + D = V

U = vergence entering lens
D = power of lens
V = vergence exiting lens

Question 4

Power of a spherical surface in a fluid

Answer 4

Ds = (n-n’)/r

n-n' = diff in refractive indices
R = radius of curvature

Question 5

Power of a thin lens immersed in fluid

Answer 5

Dair/Dfluid = [n(lens) - n(air)]/[n(lens) - n(fluid)]

Question 6

Transverse/linear magnification

Answer 6

M(L) = I/O

Image height over object height

Question 7

Axial magnification

Answer 7

Mag of depth

Max = [M(L)]^2

ie square of linear mag

Question 8

Angular magnification

Answer 8

Ma = D/4

Question 9

Vertex distance and magnification

Answer 9

1 mm increase of vertex distance

• increases mag by 0.1% x D for plus lens
• decreases mag by 0.1% x D for minus lens

Question 10

Aniseikonia

Answer 10

Every 1 D anisometropia between the two eyes produces 2% aniseikonia

Unilateral aphakes have 25% with spectacles, 7% c CTL, 2.5% c IOL.

Can usually tolerate ~6-7% (3 D).

Question 11

Astronomical telescope

Answer 11

Aka keplerian

2 plus lenses; distance apart is sum of FL
Higher power is eyepiece; inverted image

Question 12

Galilean telescope

Answer 12

Strong minus lens (eyepiece) and weak plus lens (obj). Distance btwn is sum of focal lengths

Erect image (ie loupes)

Question 13

Telescope formulas

Answer 13

Angular Mag: Ma = -De/Do

Accommodation thru telescope: At = An (Ma)^2, where An = normal accommodation

Question 14

SRK formula

Answer 14

P = A - 2.5AL - 0.9K (emmetropia)

For other target RE: Diol = P - (R/1.5), where R is desired RE

Question 15

Define:
Apical alignment
Apical bearing
Apical clearance

Answer 15

Apical alignment: RGP has same BC as K
Apical bearing: RGP has rests on K BC too flat
Apical clearance: RGP is steeper (smaller BC) than K

Question 16

Calculate the size projected onto the retina for an object of given size & given distance from the eye.

Answer 16

object height / retinal image height = distance from the eye / 17 mm

Question 17

RGP conversion: -2.50 + 0.75 x 90; k=7.65 (44.12 d) and 7.85 (43.25); base curve 7.65

Answer 17

RGP is -2.50 sph; convert to minus and drop cyl (-1.75), then add -0.75 because lens is 0.75 D steeper than FLAT K