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1. Plus / Minus Cylinder Transposition
Converts optical prescriptions between Plus-Cylinder and Minus-Cylinder formats.
Transposed Prescription Result:
SPH: -3.25CYL: +0.75AXIS: 90°Formula: New SPH = SPH + CYL | New CYL = −(CYL) | New AXIS = AXIS ± 90°
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2. Vertex Distance Compensation (Glasses ➔ Contacts)
Calculates power shift when moving lenses from 12mm spectacle distance to contact lens 0mm BVD.
Equivalent Contact Lens Power:
Contact Lens SPH: -4.72 DPower Adjustment: +0.28 DFormula: Fc = Fg / (1 − d × Fg) where d = 12mm spectacle distance.
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3. Reading & Near Vision Focal Distance Calculator
Determines precise working distance for reading glasses based on ADD power.
Ideal Working Focal Distance:
50.0 cm19.7 inchesFormula: Focal Distance = 100 / ADD Power (in cm)