Having an updated eyeglasses prescription is essential to maintain clarity in vision and avoid unnecessary eye strain. If you’ve recently had an eye examination, you may be curious about how to calculate your eye power from your prescription. In this article, we’ll walk you through the process of understanding and calculating eye power from your prescription.

1. Understand the terminology:

To calculate your eye power, it’s important to familiarize yourself with the terms listed on your prescription. Here are some common terms you might encounter:

– OD (Oculus Dexter) – Refers to the right eye

– OS (Oculus Sinister) – Refers to the left eye

– Sphere (SPH) – Indicates the lens power required for vision correction

– Cylinder (CYL) – Indicates the amount of astigmatism that needs correction

– Axis – Represents the angle (measured in degrees) at which the cylinder is placed

2. Identify the numbers:

Your prescription will have a series of numbers that represent different aspects of your vision correction. For instance:

– Sphere – This number gives you an idea of your nearsightedness or farsightedness. A minus sign (-) before the number represents nearsightedness, while a plus sign (+) denotes farsightedness.

– Cylinder – If you have astigmatism, this number indicates how severe it is. Like sphere values, minus signs indicate nearsighted astigmatism, while plus signs represent farsighted astigmatism.

– Axis – This number falls between 1 and 180 and specifies the angle required to correct astigmatism.

3. Calculate the eye power:

Start by identifying the values for Sphere, Cylinder, and Axis for each eye (OD and OS). Then follow these steps:

Step 1: Add Sphere value (SPH) and Cylinder value (CYL) to find the total refractive power needed for your lens. This calculation is the same for both nearsightedness and farsightedness.

Step 2: Write down the Axis value, as it represents the position of the Cylinder correction on your lens.

Step 3: Repeat these calculations for both OD and OS values.

Example:

A sample prescription might look like this:

OD (Right Eye): Sphere -2.00, Cylinder -1.50, Axis 90

OS (Left Eye): Sphere -3.00, Cylinder +1.00, Axis 180

Calculate eye power as follows:

Right Eye:

– Total refractive power: (-2.00) + (-1.50) = -3.50

– Axis: 90

Left Eye:

– Total refractive power: (-3.00) + (+1.00) = -2.00

– Axis: 180

4. Be mindful of additional corrections:

In some cases, there may be additional elements to your prescription, such as Prism and Base values (used to correct eye alignment issues) or Add value (for multifocal/bifocal lenses). Make sure to take these corrections into account when discussing lens options with your optician.

Conclusion:

Understanding how to calculate eye power from your prescription is a useful skill that can help you stay informed about your vision needs. Keep in mind that while it’s helpful to understand these calculations, it’s essential to visit an optometrist regularly for accurate prescriptions and sound advice on choosing the right eyewear for your specific needs.