How To Read An Eyeglass Prescription

Understanding your eyeglass prescription is crucial for selecting the right glasses to correct your vision. Although eyeglass prescriptions might appear complicated at first glance, they contain specific information that is easy to understand once you break down the terms and numbers. This guide will help you decode your prescription, explain the common terms used, and provide insights into how these details influence your choice of eyeglasses.

The Basic Structure of an Eyeglass Prescription

An eyeglass prescription typically includes several key elements:

• OD and OS: These abbreviations stand for “oculus dexter” and “oculus sinister,” which are Latin for “right eye” and “left eye,” respectively. Sometimes, you might also see OU, which stands for “oculus uterque” or “both eyes.”
• SPH (Sphere): This number indicates the lens power needed to correct nearsightedness or farsightedness. A negative number (e.g., -2.00) signifies myopia (nearsightedness), while a positive number (e.g., +2.00) indicates hyperopia (farsightedness).
• CYL (Cylinder): This number represents the degree of astigmatism, a condition where the cornea is irregularly shaped, causing blurred vision. If there is no astigmatism, this section may be blank or not included.
• AXIS: This number (ranging from 1 to 180 degrees) indicates the orientation of the astigmatism correction. It is only present if there is a CYL value.
• ADD: This is the additional magnifying power added to the bottom part of multifocal lenses for presbyopia, a condition that affects near vision as people age. It is commonly found in prescriptions for bifocals or progressive lenses.
• PD (Pupillary Distance): This measurement, often in millimeters, is the distance between the centers of your pupils. It guarantees that the lenses are placed in front of your eyes in the ideal position for clear vision.

Detailed Breakdown of Prescription Components

1. Sphere (SPH)

• The sphere value corrects for nearsightedness or farsightedness.
• A negative SPH number (e.g., -2.50) means you are nearsighted and require concave lenses to correct your vision.
• A positive SPH number (e.g., +1.75) indicates you are farsighted and need convex lenses.

2. Cylinder (CYL)

• The cylinder value corrects astigmatism, which is caused by an irregularly shaped cornea or lens.
• This value can be positive or negative, and if there is no astigmatism, this section is often left blank.

3. Axis

• The axis value provides the orientation of the astigmatism correction.
• It is a number between 1 and 180 and is only present if there is a CYL value.
• This number tells the eyeglass maker the angle at which to place the cylinder correction on the lens.

4. Add

• The added value is used for bifocals or progressive lenses.
• It represents the additional magnifying power needed for reading or close-up work.
• Typically, this number ranges from +0.75 to +3.00.

5. Pupillary Distance (PD)

• PD is crucial for proper lens placement in the frames.
• It guarantees that the lenses are placed in front of your eyes in the ideal position for clear vision.
• PD can be a single number (e.g., 63 mm) or a split number (e.g., 31/32 mm) for each eye.

Example of an Eyeglass Prescription

To illustrate, let’s examine a sample prescription:

• OD: -2.50 SPH -1.00 CYL 180 AXIS
• OS: -1.75 SPH -0.50 CYL 170 AXIS
• ADD: +2.00 (both eyes)
• PD: 62 mm

In this example:

• The right eye (OD) has a nearsighted correction of -2.50 diopters, an astigmatism correction of -1.00 diopters, and the cylinder axis is positioned at 180 degrees.
• The left eye (OS) has a nearsighted correction of -1.75 diopters, an astigmatism correction of -0.50 diopters, and the cylinder axis is at 170 degrees.
• The ADD value of +2.00 indicates additional magnifying power for reading or close-up work.
• The PD of 62 mm ensures the lenses are centered correctly in front of the eyes.

Interpreting Your Prescription for Lens Selection

Once you understand your prescription, you can make informed decisions about your eyeglasses. Here are some considerations:

1. Single Vision Lenses:

• These lenses have the same corrective power across the entire lens.
• Ideal for people who need correction for either nearsightedness or farsightedness without astigmatism.

2. Bifocal and Trifocal Lenses:

• These lenses have two or three distinct areas with different corrective powers.
• Bifocals are typically for distance and near vision, while trifocals include an intermediate section.

3. Progressive Lenses:

• These lenses provide a smooth transition between multiple corrective powers, from distance to near vision.
• They offer a more natural visual experience compared to bifocals or trifocals.

4. Lenses for Astigmatism:

• Toric lenses are designed to correct astigmatism and are available in both single-vision and multifocal options.

5. High-Index Lenses:

• For strong prescriptions, high-index lenses are thinner and lighter, providing better aesthetics and comfort.

Conclusion

Reading and understanding your eyeglass prescription is essential for selecting the right glasses and ensuring optimal vision correction. By familiarizing yourself with the terms and numbers used in your prescription, you can make informed choices about your eyewear. Whether you need single-vision lenses for nearsightedness, bifocals for presbyopia, or toric lenses for astigmatism, your prescription holds all the information necessary to address your specific vision needs. If you have any doubts or need further clarification, consulting with your eye care professional is always a good idea to ensure you get the best possible vision correction.

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