Equations

Question 1

Snellen Fraction, V

Answer 1

V= d/D

d= testing distance - 6m is standard

D= distance at which limbs of the last line of the letters correctly identified subtend 1’ arc

Question 2

Decimal V

Answer 2

1/MAR

MAR in ‘ of arc

Question 3

Power of thin lens

Answer 3

F = -n/f

= n’/f’

Question 4

Paradise Surface Power

Answer 4

F= (n’-n)/r

Question 5

Retraction equation

Answer 5

L’=L+F

Question 6

Change in Ocular Refraction

Answer 6

-2.7(change in k’)

Question 7

Ocular Refraction for fully corrected eye

Answer 7

Fsp/ (1-dFsp)

Question 8

Traverse Magnification

Answer 8

L/L’ = h’/h

Question 9

Mtotal

Answer 9

L1/L1’ = L2/L2’

Question 10

L2

Answer 10

=L1/(1-dL1’)

Question 11

Image height for distant objects

Answer 11

h’= -ntanx/Fe

Question 12

Blur circle for Distance Vision

Answer 12

b=p(K/K’)

Question 13

Basic Blurred Image Height

Answer 13

h’b= h’(Fe/K+Fe)

Question 14

Blur Ratio

Answer 14

BR= -pK/tanw

Can change w to work out Br for diff letters eg for 6m letter use 5’arc

Question 15

Projected blur

Answer 15

D x p x K

Question 16

Spectacle Magnification

Answer 16

1+dK

Or

K/Fsp

Question 17

Length of Line Foci (Astigmatism)

Answer 17

AST= Fex+90 - Fex

In the x+90 a= p(Ast/ Fex+90)

In the x meridian b=p(-Ast/Fex)

Question 18

Dioptric location of the DLC

Answer 18

L2’ = (Fex+90 + Fex)/2

Question 19

Size of the DLC, z

Answer 19

Z=(p x Ast)/ 2K’

Question 20

Amplitude of Accommodation

Answer 20

Amp=K-B

Question 21

Range of Accommodation

Answer 21

b-k

Question 22

Ao for emmetropes

Answer 22

-L

Or If object distance is measured from spectacle plane

-Ls/(1-dLs)

Question 23

As for emmetropes

Answer 23

-Ls

Question 24

Ao for Ametropes

Answer 24

K - L2

L2= Ls + Fsp/ 1-d(Ls+Fsp)

Question 25

As for ametropes

Answer 25

Ls’ - Fsp - Ls

Question 26

Add

Answer 26

-Ls - 0.5Amps