Transposition and Toric Transposition
Rules for Transposition Axis will be changed from the 90 degree apart Cylinder sign will be changed Cylinder value will remain same Spherical power will be adjusted to cylinder value
Partha Haradhan Chowdhury1*, Brinda Haren Shah2 and Nripesh Tiwari3
1.M.Optom, Associate Professor, Principal, Department of Optometry, Shree Satchandi Jankalyan Samiti Netra Prasikshan Sansthan, Pauri, Affiliated to Uttarakhand State Medical Faculty, Dehradun, India
2.M.Optom, Guest Lecturer, Department of Optometry, Shree Satchandi Jankalyan Samiti Netra Prasikshan Sansthan, Pauri, Affiliated to Uttarakhand State Medical Faculty, Dehradun, India
3.D.Optom, General Secretary and Chief Optometrist, Department of Optometry, Shree Satchandi Jankalyan Samiti Netra Prasikshan Sansthan, Pauri, Affiliated to Uttarakhand State Medical Faculty, Dehradun, India
*Corresponding author: Partha Haradhan Chowdhury, M. Optom, Department of Optometry, Shree Satchandi Jankalyan Samiti Netra Prasikshan Sansthan, Pauri, Affiliated to Uttarakhand State Medical Faculty, Dehradun, India, Email: optometrypublish@gmail.com
Introduction
Rules for Transposition
- Axis will be changed from the 90 degree apart
- Cylinder sign will be changed
- Cylinder value will remain same
- Spherical power will be adjusted to cylinder value
Examples
- A. +4.00 Ds / +4.00 Dcyl*90
- Rule about Axis – Here, axis will be 180
- Cylinder sign – Here, cylinder value will be in minus form
- Cylinder value will be same
- Spherical power will be adjusted to spherical value Here, [+4.00 + (+4.00)] = [+8.00]
- So, final answer will be +8.00 Dsph / -4.00 Dcyl*180
- B. +8.00 Dsh/-4.00 Dcyl*90
- +8.00 + (-4.00)/+4.00*180
- +(8.00) – (4.00)/+4.00*180
- +4.00/+4.00*180
Toric Transposition
Example 1
First Step
Prescription cylinder sign will be matched with the base curve sign.
Eg:
Suppose: [Base curve = -6.00]
Prescription: -2.00/+5.00*180
Here, Base curve is in minus form and prescription cylinder is in plus form, so transposition is needed [1].
- -2.00 + (+5.00)/-5.00*90
- +3.00/-5.00*90
Second Step
Always minus will be done between Base curve and spherical power.
- Here, spherical power is +3.00D and Base curve is -6.00D So, +3.00-(-6.00)
- +3.00 + 6.00
- +9.00
It will be used on the tool.
Third Step
Base curve axis will be completely perpendicular to the final prescription axis (after transposed) [2].
So, -6.00*180
Fourth Step
Always addition will be done between Base Curve and cylinder [3].
So,
$$\text{BC} = -6.00$$
$$\text{Cylinder} = -5.00$$
$$-6.00 + (-5.00)*90$$
$$-6.00 - 5.00 * 90$$
$$-11.00*90$$
Final,
+9.00
-6.00*180 / -11.00*90
Example 2
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
$$+2.00 / -5.00*180$$
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
$$-6.00*90$$
Fourth Step
Add Base curve and cylinder power
$$-6.00 + (-5.00)*180$$
$$-11.00*180$$
So, final
-8.00
-6.00*90 / -11.00*180
References
-
1 William J Benjamin (2006) Borish's Clinical Refraction 2nd (Edn.). 2 Theodore Grosvenor, Theodore P Grosvenor (2007) Primary Care Optometry. 5th (Edn.). 3 Sir Stewart Duke-Elder, David Abrams (1978) Duke-Elder's Practice of refraction.
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