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Spherical Equivalent Formula:
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The Spherical Equivalent (SE) is a way to simplify a sphero-cylindrical prescription into a single value by combining the sphere and half of the cylinder power. It's particularly useful for contact lens fitting and certain refractive procedures.
The calculator uses the Spherical Equivalent formula:
Where:
For contact lenses: The calculator also applies a vertex distance adjustment to account for the difference between glasses and contact lens positioning.
Details: Spherical equivalent is crucial for contact lens fitting, determining the dominant eye in monovision, and planning certain refractive surgeries. It provides a simplified representation of the refractive error.
Tips: Enter your sphere and cylinder values in diopters, select whether you're calculating for glasses or contact lenses. The calculator will provide the spherical equivalent with appropriate adjustments.
Q1: Why is spherical equivalent important for contact lenses?
A: Many contact lenses come in spherical powers only, so the spherical equivalent helps approximate the needed power when converting from glasses prescriptions.
Q2: What's the difference between glasses and contact lens SE?
A: Contact lenses sit closer to the eye than glasses, requiring a vertex distance adjustment, especially for higher powers.
Q3: When is spherical equivalent not appropriate?
A: For patients with significant astigmatism (>1.50D) or when precise vision correction is critical, the full sphero-cylindrical prescription should be used.
Q4: How accurate is the vertex distance adjustment?
A: The adjustment is an approximation. Actual fitting should be done by an eye care professional.
Q5: Can I use this for toric contact lenses?
A: Toric lenses correct astigmatism directly, so spherical equivalent is less relevant. This calculator is primarily for spherical contact lenses.