Spectacle power transpose one form to another?

Hello friends welcome to our ophthal Mcq blog site. Our site is mainly focusing on Optometry and Ophthalmology related study material, term, multiple choice questions (mcq), we also serve free ebook pdf, some questions regarding the Optometrist and Ophthalmology.

In today's blog website are going to discuss step by step about how to transpose spectacle power one form to another. This is very important topic and information for who is think go in dispensing Optometry. In dispensing Optometry is very deep about spectacle glasses and contact lenses. Each person who already in or who thinking to dive into dispensing Optometry kindly read this blog carefully.

So friends, spectacle power consists Spherical, cylinder and its axis. transposition is nothing but it's only mathmatical interchange of these three components, let's see its rule. It has some Basic and simple rule. 

Rule of spectacle transposition.

  1. Rule: Addition of Spherical and cylindrical power.
  2. Rule: Keep the Cylindrical power same only change it's sign.
  3. Rule: Rotate the axis of Cylindrical. if axis is equal to 90° or less than 90° rotate it by adding 90° and you'll get the axis. OR If the axis is more than 90° rotate it by subtracting 90° from that axis and you'll get the Axis.

I hope this rule you found helpful and easy to understand. If not don't worry we have solved example how to transpose spectacle power using these three simple rule.

Example 1: spectacle power is (SPH+1.50, CYL+1.00, AX 20)

Step 1. According to our first rule Addition SPH and CYL, after addition we get (+1.50+ 1.00)= SPH+2.50.

Step 2. According to our second Rule keep the Cylindrical power as it is, only change it's sign (previously plus became minus & previously have minus became plus). Now we previously have (CYL+1.00) it's become CYL-1.00.

Step 3. According to our third rule, we previously have axis 20 means it's less than 90°. Our third Rule say's if Axis is equal 90° to or less than 90° you have to add 90° into it ok. Now let's see what axis we get, (20°+90°)=110°Axis.

Now we done, we find transpose spectacle power which is: SPH+2.50, CYL-1.00, AX110°.

We have mentioned both power:
Original power  : +1.50+1.00*20
After transpose: +2.50-1.00*110, Visual acuity of patient with this two different power is same. only it's form get change. I hope you'll get it, please do practice on it. you still don't understand please let us know in comments box. (For calculation you must know Rule of addition and how minus & plus sign play role in addition).

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