1. What is Spherical Equivalent?

The Spherical Equivalent (SE) is a calculation used in ophthalmology to convert a sphero-cylindrical prescription into a single spherical value. It represents the average power of the lens meridian and is useful for contact lens fitting, refractive surgery planning, and simplifying prescriptions.

2. How Does the Calculator Work?

The calculator uses the Spherical Equivalent formula:

Where:

• \( SE \) — Spherical Equivalent (diopters)
• \( S \) — Sphere component of the prescription (diopters)
• \( C \) — Cylinder component of the prescription (diopters)

Explanation: The formula averages the power of the prescription by adding half of the cylinder power to the sphere power.

3. Importance of Spherical Equivalent

Details: Spherical Equivalent is crucial for contact lens fitting (especially spherical lenses), planning refractive surgery, and simplifying prescriptions for patients who cannot tolerate astigmatic correction.

4. Using the Calculator

Tips: Enter both sphere and cylinder values in diopters (can be positive or negative). The calculator will automatically compute the spherical equivalent.

5. Frequently Asked Questions (FAQ)

Q1: When is spherical equivalent used clinically?
A: Commonly used for contact lens fitting, refractive surgery planning, and when simplifying prescriptions for patients with low astigmatism.

Q2: How accurate is spherical equivalent?
A: It provides a good approximation but doesn't fully account for astigmatic correction. Some patients may still need full sphero-cylindrical correction.

Q3: Can spherical equivalent be negative?
A: Yes, if the sphere is negative and larger than half the cylinder value, the SE will be negative.

Q4: Does axis affect spherical equivalent?
A: No, the axis is not used in the SE calculation as it only considers the power components.

Q5: What's the difference between SE and manifest refraction?
A: Manifest refraction includes full sphero-cylindrical correction, while SE simplifies it to a single spherical value.