Transposition an application of changing the lens power from one to another. Usually it is changed from ‘+’ form to ‘–‘ form.

1. Simple & Toric Transposition
Md: Azizul Islam, Junior Optometrist
Oculoplasty Department
Ispahani Islamia Eye Institute & Hospital
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2.  Transposition an application of changing the lens power
from one to another.
 Usually it is changed from ‘+’ form to ‘–‘ form.
Definition
Transposition two types :
1.Simple &
2.Toric Transposition
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3.  Algebric sum of sphere and cylinder ,To gate a new sphere.
 Cylindrical power will be same, but
 Sign and axis of cylinder will be in opposite ( 90 Degree apart angle).
 Examples:
 +2.5 D Sph / +3.0 D cyl x 150*
 a) + 5.5 D Sph
 b) 3.0 D cyl
 c) – cyl & 60*
 Final Rx : + 5.5D Sph / -3.0D Cyl x 60*
Rules –Simple transposition
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4. 1) -1.5 D Sph / -4.0 D Cyl x 105*
Answer : -5.5 D Sph / + 4.0D Cyl x 15*.
2) + 2.0 D Cyl x 90*
Answer : + 2.0 D Sph / -2.0D cyl x 180*
3) -1.5 D Sph / + 4.0 D Cyl x 105*
Answer : + 2.5 D Sph / -4.0 D Cyl x 15*
Few Examples
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5. Sphere into two cylinders.
+3.0D Sph = +3.0D cyl 90* / +3.0D cyl 180*
Cylinder into sphero-cylinder.
+3.0D cyl 90* = +3.0D Sph / -3.0D cyl 180*
Sphere-cylinder into
 Alternate Sphero-cylinder.
 Two cylinders.
Different Methods Of
Simple Transposition
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6.  Objective: To select the proper tools in cylinder lens surfacing.
 Rules:
 1.Choose the Base curve first for proper curvature.
 2.Do simple transposition if sign of base curve &cylinder not same.
 3.To find out the spherical surface power,
 Subtract the base curve from sphere.
 4.To find out the cylindrical surface power,
 Fix the Base curve at the right angle to the axis of cylinder.
 Add the base curve with cylinder
 5.Both spherical & cylindrical surface determines the lens power.
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7.  Example:
 + 1.0 D Sph / + 2.0 D Cyl x 165* (-6.0 Base curve)
 + 3.0 D Sph / -2.0D Cyl x 75*
 + 3.0 – ( -6.0) = + 9.0 D Sph.
 -6.0D Cyl x 165*
 -2.0 + ( -6.0) = -8.0D Cyl x 75*
+ 9.0D Sph
 :
-6.0D Cyl x 165*/ -8.0D Cyl x 75*
Toric Transposition
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8. 1) +1.0D Sph / +2.0D Cyl x 180* ( +6 Base)
-5.0D Sph
 :
+ 6.0D Cyl x 90* / + 8.0D Cyl x 180*
2) –3.0D Sph / -1.5D Cyl x 90* ( -6 Base)
+ 3.0D Sph
 :
-6.0D Cyl x 180 / -7.5 D Cyl x 90*
Examples...
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9.  Prescription -3.00/+5.00*90
Base curve -6.00
 First Step:
Transpose the prescription so that base
curve sign will be
similar to the base curve sign
 +2.00/-5.00*180
Example Review:
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10. Second Step:
Minus should be done between spherical and base curve power.
 -6.00 – (+2.00)
 -6.00 - 2.00
 -8.00
It will be used in a tool
Third Step:
Base curve axis will be completely perpendicular with the
prescription (which is transposed) So, axis will be
 -6.00*90
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11. Fourth Step:
Add Base curve and cylinder power
 -6.00 + (-5.00)*180
 -11.00*180
So, Final :
-8.00 Sph

-6.00 Cyl*90 / -11.00 Cyl*180
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12. A sphero-cylinder lens will correct for astigmatism and myopia or hyperopia. If it was
necessary to correct a nearsighted or farsighted person who also has astigmatism, but
there were no cylinder lenses available, what would be the best correction using only a
sphere lens.
How to Find the Spherical equivalent :
1. Take half the value of the cylinder and
2. Add it to the sphere power.
In other words, as a formula the spherical equivalent
Spherical Equivalent = Sphere + (Cylinder)/2
Example: +3.00 − 1.00 × 180º
spherical equivalent = +3.00 + (-1.00) /2 = +2.50D
Spherical Equivalent
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13. IIEI&H
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