1. What is Spherical Equivalent (SE)?

The Spherical Equivalent (SE) is a calculation used in ophthalmology to convert a sphero-cylindrical prescription into a single spherical power. It's particularly useful for contact lens fitting and simplifying prescriptions.

2. How Does the Calculator Work?

The calculator uses the Spherical Equivalent formula:

Where:

• \( Sphere \) — Spherical power in diopters (D)
• \( Cylinder \) — Cylindrical power in diopters (D)

Explanation: The formula accounts for the combined refractive power by adding half of the cylindrical power to the spherical power.

3. Importance of SE Calculation

Details: Spherical equivalent is crucial for contact lens fitting, especially when toric lenses aren't available or needed. It provides an approximate single power that can correct vision reasonably well.

4. Using the Calculator

Tips: Enter both sphere and cylinder values in diopters (D). Values can be positive or negative and typically range from -20.00 to +20.00 in 0.25 D increments.

5. Frequently Asked Questions (FAQ)

Q1: When is spherical equivalent used in practice?
A: Commonly used for contact lens fitting, especially spherical soft lenses, and for estimating refractive error in research studies.

Q2: Does SE work for all patients?
A: No, patients with high astigmatism (>1.50 D) may not tolerate SE correction well and may need toric lenses.

Q3: How accurate is SE for vision correction?
A: SE provides functional vision but not optimal correction for astigmatism. Visual acuity may be slightly reduced compared to full sphero-cylindrical correction.

Q4: Should axis be considered in SE calculation?
A: No, axis isn't used in SE calculation as it's only concerned with power, not orientation of the astigmatism.

Q5: Can SE be used for spectacle prescriptions?
A: Rarely, as spectacles typically provide full sphero-cylindrical correction. SE is mainly used when simplification is needed (contact lenses, research).