1. What is Spherical Equivalent?

The Spherical Equivalent (SE) is a calculation used in optics to convert a sphero-cylindrical lens prescription into a single spherical power. It represents the average power of the lens meridian.

2. How Does the Calculator Work?

The calculator uses the Spherical Equivalent formula:

Where:

• \( SE \) — Spherical Equivalent (diopters)
• \( Sphere \) — Spherical power (diopters)
• \( Cylinder \) — Cylindrical power (diopters)

Explanation: The formula averages the power of the two principal meridians of the lens.

3. Importance of Spherical Equivalent

Details: SE is used in contact lens fitting, refractive surgery planning, and when simplifying prescriptions for patients who can't tolerate astigmatic correction.

4. Using the Calculator

Tips: Enter both sphere and cylinder values in diopters. The cylinder value can be positive or negative depending on the prescription notation.

5. Frequently Asked Questions (FAQ)

Q1: When is spherical equivalent used clinically?
A: Commonly used for contact lens fitting (especially spherical lenses), IOL power calculations, and some refractive surgery procedures.

Q2: Does spherical equivalent affect visual acuity?
A: It may reduce visual acuity in patients with significant astigmatism, as it doesn't fully correct the cylindrical component.

Q3: How accurate is spherical equivalent?
A: It provides a good approximation but isn't a perfect substitute for full sphero-cylindrical correction in patients with significant astigmatism.

Q4: Can I use this for toric contact lenses?
A: No, toric lenses require the full sphero-cylindrical prescription, not just the spherical equivalent.

Q5: What's the difference between SE and manifest refraction?
A: Manifest refraction includes both sphere and cylinder components, while SE combines them into a single spherical value.