Optometry Toolkit — Complete User Guide

Spherical Equivalent Calculation

Formula: SE = Sph + 0.5 × Cyl

Spherical equivalent combines sphere and cylinder into a single equivalent diopter value, used for IOL calculation, myopia progression assessment, and anisometropia evaluation.

Examples

• -3.00 DS / -1.00 DC × 180 → SE = -3.00 + 0.5×(-1.00) = -3.50D
• +2.00 DS / +1.50 DC × 90 → SE = +2.00 + 0.5×(+1.50) = +2.75D

Prescription Conversion

Optical equivalence principle: sphere difference = difference of two cylinders, new axis = old axis ± 90°

Example: -2.00 DS / -1.00 DC × 180 → Converted to: -3.00 DS / +1.00 DC × 90

Jackson Cross-Cylinder (JCC)

Uses

• Fine-tuning precise astigmatism axis and power
• Measuring fusional crossed cylinder (FCC) in presbyopia refraction

JCC Reading Method

Place red/white dots on each side of expected axis; compare clarity with flip method:

• When both directions are equally clear, current axis is the precise axis
• When one direction is clearer, adjust axis toward that direction

References

• Benjamin WJ. Borish's Clinical Refraction. 2nd ed. Butterworth-Heinemann, 2006.