Vision Prescription Converter Calculator
Plus/Minus Cylinder Transpose
Convert between plus and minus cylinder notation
D
D
degrees
Understand Your Prescription
Enter your prescription to understand what each value means
D
D
D
Formula
Cylinder Transpose: New SPH = SPH + CYL | New CYL = -CYL | New AXIS = AXIS +/- 90 | Spherical Equivalent = SPH + (CYL / 2)
Frequently Asked Questions
What do SPH, CYL, and AXIS mean?
SPH (sphere) corrects myopia (minus) or hyperopia (plus). CYL (cylinder) corrects astigmatism. AXIS (1-180 degrees) indicates the orientation of astigmatism. Together they define the lens power needed.
What is the difference between plus and minus cylinder?
They are two ways to write the same prescription. Ophthalmologists typically use plus cylinder; optometrists use minus cylinder. Transposing converts between them: add CYL to SPH, negate CYL, rotate AXIS by 90 degrees.
What is spherical equivalent?
Spherical equivalent (SE) = SPH + (CYL / 2). It represents the overall refractive error as a single number and is commonly used for contact lens fitting and refractive surgery planning.
Can I use my glasses prescription for contacts?
No. Contact lens prescriptions differ from glasses prescriptions because contacts sit directly on the eye. For prescriptions stronger than about +/-4.00 D, a vertex distance adjustment is needed. Contact lenses also require base curve and diameter measurements.
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