Convert Eye Prescription To 20/20 Scale Calculator
Estimate Snellen visual acuity (20/20 scale) from your eyeglass prescription using sphere, cylinder, axis, and age.
Published by:
isCalculator Editorial Team
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How to use this tool?
How to Use the Eye Prescription to 20/20 Scale Calculator
- Enter Sphere (D): Input your sphere value in diopters (e.g., -2.00 for myopia or +1.50 for hyperopia). Negative values indicate nearsightedness; positive values indicate farsightedness.
- Enter Cylinder (D) (optional): Input your cylinder value for astigmatism (usually negative, e.g., -0.75). Leave as 0 if you have no astigmatism.
- Enter Axis (°) (if cylinder is non-zero): Provide the axis angle between 0 and 180 degrees (e.g., 180). This is required only if cylinder is not zero.
- Enter Age: Input your age (minimum 1). The calculator adjusts for age-related vision changes after 40.
- Click "Calculate 20/20 Equivalent": The tool computes your estimated Snellen visual acuity (e.g., 20/40) using a spherical equivalent formula and age adjustment.
Output: You’ll see your Snellen fraction (e.g., 20/25) and a breakdown of the calculation steps, including spherical equivalent and logMAR values.
Note: This is an estimate only. Always consult an eye care professional for accurate prescriptions.
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Frequently Asked Questions
This calculator provides a rough estimate based on a simplified model. Actual visual acuity depends on many factors including corneal health, lens clarity, and neural processing. Consult an eye care professional for accurate assessment.
Spherical equivalent (SE) is calculated as Sphere + (Cylinder / 2). It represents the single spherical power that would provide the same overall focus as the combination of sphere and cylinder.
The model includes a slight age adjustment because visual acuity tends to decline gradually with age, especially after 40, due to factors like presbyopia and increased light scatter.
