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Prescription change
I went to the eye doctor today and was so surprised to learn that my prescription has changed quite a bit in a short amount of time. I had an exam in Sept. 06 and my Right eye was : Sphere +4.50 Cylinder + 4.00 and Axis 86. Left eye: Sphere +4.50 Cylinder + 2.25 and Axis 96. My current prescription is Right eye: Sphere +8.25 Cylinder -3.25 Axis 175 and Left eye Sphere +6.50 Cylinder -2.50 and Axis 012. I am 37 and have always worn glasses. I go to the Dr. regularly to ensure that my eyes are healthy. Is it possible that the Dr. made an error or is it possible for my farsightedness to have increased so dramatically? Thanks for your response.
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Hello ediegirl,    There is really very little difference in those two prescriptions. One is written in PLUS CYLINDER notation and the other is MINUS CYLINDER notation.

I borrowed this from a website if you interested in how the two are interchanged.

Not to worry. You are howeve very farsighted and this can sometimes cause crossed eyes or strabismus in infants and children and angle closre glaucoma in older adults. See an ophthalmologist year.

JCH III MD

Transposition

Transposing a glasses prescription is simply converting the prescription from minus cylinder notation to plus cylinder notation. The optical properties of the prescription remain the same.

Procedure:

1) Algebraically add the cylinder power to the sphere power to arrive at the new sphere power.

2) Change the sign of the cylinder power.

3) Add or subtract 90 from the axis.

Example 1— Transpose the following prescription:

+2.00 – 2.50 x 105

1)  +2.00 – 2.50 = - .50 (new sphere)

2)  -2.50 changes to +2.50 (new cyl.)

3)  105 – 90 = 15 (new axis)

-.50 +2.50 x 15

Example 2 —

+1.00 + 3.00 x 35

1)  +1.00 + 3.00 = +4.00

2)  +3.00 changes to – 3.00

3)  35 + 90 = 125

+4.00 – 3.00 x 125

Why are there plus and minus cylinders? Plus cylinder lenses exist only in phoropters and trial lenses. Glasses lenses are made in minus cylinder. Plus cylinder phoropters are popular because it is easier to teach retinoscopy in plus cylinder. Ophthalmologists typically learn retinoscopy and refraction in plus cylinder. Optometrists typically use minus cylinder.

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