Equations

Question 1

Index of refraction:
Air
water
Aqueous
Vitreous
Cornea

Answer 1

1

1. 33
2. 34
3. 34
4. 37

Question 2

Index of refraction: 
Crystalline lens
PMMA
Crown Glass
high index lenses

Answer 2

1. 42
2. 49
3. 52
4. 6-1.8

Question 3

Refracting power of a spherical surface

Answer 3

D = (n1-n)/r

Question 4

Refractive power in two different media

Answer 4

D(media1)/D(media2) = (Nobject-Nmedia1)/(Nobject-Nmedia2)

Solve for missing variable

Question 5

focal length

Answer 5

1/D (lens power in diopters

Question 6

Vergence

Answer 6

U+D=V
U= vergence of rays entering the lens
D = vergence of the lens
V= vergence of rays leaving the lens

Question 7

Prentice’s Rupe

Answer 7

PD = h (cm) x D (lens power)

Question 8

retinal image size (based on model eye)

Answer 8

object ht/retinal image ht = distance from nodal pt/ 17 mm

Question 9

spectacle lens magnification

Answer 9

M (mag of spectacles) = 2%xD (lens power)
Plus lens magnify
Minus lens minify

Question 10

Transverse Magnification

Answer 10

M (trans) = Image distance/Object distance

Question 11

Axial magnification

Answer 11

M axial = (M transverse)squared

Question 12

Simple magnifier (angular mag)

Answer 12

M = D (lens power) / 4

standard reference distance of (0.25 cm) If different distance replace 1/4 with new distance)

Question 13

Telescope

Answer 13

M = D eyepiece/ D objective

Question 14

Reflecting power of a mirror

Answer 14

D (power) = 1/f = 2/r

Question 15

SRK formula

Answer 15

D = A constant - 2.5 AL - 0.9 K(avg)

Question 16

changing VD for plus lens vs minus lens

IOL power vs spectacle power

Answer 16

Plus lenses become more powerful as VD increases and less powerful as VD decreases
1.5 D IOL power for every 1 D spectacle lens power
MInus lens become less powerful with incr VD and more powerful with decreased VD.

Question 17

Tilting plus and minus lens

Answer 17

tilting a plus lens = induces plus cylinder in axis of tilt

Tilting a minus lens induces minus cylinder in the axis of tilt

Question 18

contact lens fitting

Answer 18

Convert to minus cylinder spherical equivalent to 0 vertex distance
Choose base curve +0.5 D (or 1/3 total astig) steeper than FLATTER K
Subtract the +.50 D from the sphere value of the refraction to obtain final value

Question 19

Astronomical telescope vs Galilean telescope

Answer 19

focal points coincide for 2 plus lenses.
Forms inverted image

vs

plus lens objective, minus lens eyepiece
upright image

Question 20

Accomodation with glasses vs CL

Answer 20

hyperopes must accomodate more through glasses than CL

Myopes accomodate less through glasses than CL

Question 21

Mirrors

Answer 21

Convex - like minus lenses
Concave - like plus lenses
(flip the direction of light - think opposite signs of transparent lens)