The document discusses the concept and methods of transposition in optics, specifically how to convert lens prescriptions from one notation to another. It details simple transposition and toric transposition with steps and examples for clarity. The document also covers the calculation of spherical equivalents and provides practical applications for correcting astigmatism and myopia or hyperopia.

1. Transposition
 Presentation by
 Saroj sah
 Rama university
 Kanpur, UP

2. Transposition
 Transposition is the process of changing a lens from
one form to another Equivalent form.
 I,e prescription from plus cylinder notation to minus
cylinder notation.
 Types of Transposition :-
 1) simple transposition
 2) Toric transposition
 Let discuss one by one

3. Simple transposition
 Three simple step:-
 A) SUM :-Algebric sum of sphere and cylinder to get a
new shpere
 Example :- +1.0Dsph/-3.0Dcyl×90
 -2.0 Dsph
 B) SIGNS :-Retain the power of the cylinder but change the sign.
 +3DC
 C) AXIS :- Rotate the axis of the cylinder through 90 degree.
 ( add 90 if ≤90 )
 ( subtract 90 if ≥90 )
 -2.0 Dsph/+3.0 Dcyl ×180

4.  Different method of simple transposition:-
 1) –ve sphero cylinder
 +3.00/-2.00x90
 2) +ve sphero cylinder :-
 +2.00/+1.50x90
 3) Crossed cylinder forms :-
 +1.00x90/+1.00x180
 Example :-
 +1.00/-0.50x180
 Step-1 +0.50/
 Step-2 +0.50/+0.50
 Step-3 +0.50/+0.50x90
 Final power +0.50/+0.50x90

5. Example of simple transposition
 1) +2.00DS/+1.00DC×180
 Ans +3.0 DS/-1.0 DC X90
 2) -3.0 DS/ -2.0 DC X 50
 Ans -5.0 DS / +2.0 DC x 140
 3) +3.50 DS / -4.0 DC x 60
 Ans -0.50 DS / +4.0 DC x 150

6. Cross cylinderical form
 Example :- +3.00/+2.00x90
 +3.00
 +3.00
 +2.00 = +5.00
 +3.00x90/ +5.00x180

7. Toric transposition
 Toric lens is one in which one surface is spherical and other is
cylindrical.and surface in which both meridians having
different power is called ‘toric surface”
 The principal meridian of weaker power of the toric surface is
known as Base curve of the lens.
 Toric forms = Sphere curve
 Base curve / Cylinder curve
 RULES:-
 1) Choose the base curve first for proper curvature.
 2) Do simple transposition if sign of base curve and cylinder is
not same.
 3) To find spherical surface power
 - subtract base curve from sphere

8.  4) To find out the cylinder surface power
 - fix the base curve at the right angle to the
axis of cylinder.
 - Add the base curve with cylinder
 5) Then both the spherical and cylinder surface
determines the lens power.
 Example of toric transposition :-
 1) +2.0 DS / +3.0 DC x 90 ( Base curve -6.0)
 Step -1 Simple transposition because Base curve and
cylinder value is not same.
 +5.0 DS / -3.0 DC X 180

9.  Step-2 Subtracting Base curve from sphere to get
spherical surface power.
 +5.0-(-6.0)= +11.0 Ds
 Step-3 Finding Cylinder surface power
 - Fixing Base curve at right angle to the axis of
cylinder i,e -6.0 DC X 90
 Step-4 Adding Base curve to the Cylinder.
 -3.0 + ( -6.0 ) = - 9.0 DC X 180
 Toric form = +11.0 DS
 - 6.0 DC X90 / -9.0 DC X 180

10. SPHERICAL EQUIVALENT
 A Spherocylinder lens wil correct for Astigmatism and
myopia or Hyperopia.
 It was necessary to correcrt a near or far- sighted who
has no astigmatism.
 If there is no cylinder lens avaliable.
 Uses of spherical equivalent :-
 It is use for the spherical lens which would convert a case
of simple.coumpound,or unequally mixwd astigmatism
into case of eually mixed astigmastism.

11. How to find the spherical equivalent
 Step-1 Take half of the value of the cylinder
 Step-2 Add it to the sphere power.
 Formula :-
 Spherical equivalent :- Sphere + Cylinder
 2
 Example :- +2.0 / 3.0 X180
 Spherical equivalent :- +2.0 + 3.0 =3.5 D
 2

12.  Hy friends if you are not understand my slideshare, then
go my Youtube channel “Optometrist Nepal” I have
present same slide on my channel.And also please like
and subscribe my youtube channel.
Thank you all of you