Equations to memorise

Question 1

Equations for step along

Answer 1

SO l2= l1’- t/n’

Question 2

BVP and FV’

Answer 2

FV’= F1/1- (t/n’)F1+ F2
Fv= F2/ 1-(t/n’) F2 + F1

OR FOR Fv’ do steps along with L1=0 and L2’= back vertex power

1/power= focal length

Question 3

Ocular vergence and refraction

Answer 3

So l2’=1/L2’
So l3= l2’-BVD
L3= 1/l3

L3= ocular vergence
Ocular refraction is vergence at corneal apex when initial vergence is 0 so redo step along with L1=0. Ocular vergence you cam just use the value for l2’ you got previously

Question 4

Bifocal centration p=CF

Answer 4

X= YA/ (F+A)

Y= separation between OD and OS. In cm
X = separation between OD and ON
A= add

Question 5

Jump

Answer 5

P= c times add (D)

C is distance from segment top to segment centre. Baso radius for round segs or down curves
For the segment

Question 6

TCA and add

Answer 6

TCA= p/v (D) prisms over abbé number. Tolerated up to 0.1 dioptres
ADD= FNear- Fdistance. Keep cyl same unless needs to be transposed

Question 7

Prism induced convergence and differential prisms with segment sizes

Answer 7

Prism induced= (inset- convergence (cm) times add)
Convergence= distance pd- near pd/2 (then divide total prism by 2 for each eye and you add your values together and then do p=cf to work out c or the amount you need to change the inset by, last q for Multifocals 2 check this again)

Diff prisms= (r2-r1) times add

Distance= OD-> NVP and near= NVP-> OS