What is CYL in an eye prescription?

CYL or cylinder in your eyes shows irregularity in the shape of your eyes which is also known as astigmatism.

What is SPH in an eye prescription?

SPH in your eye prescription refers to the power that is required to correct your vision. If it is a negative number it means you are short-sighted and if it’s a positive number, it means you are long-sighted.

How do you read a prescription OD and OS?

OD is an abbreviation for oculus dexter in Latin which means your right eye. While OS stands for Oculus Sinister in Latin which means your left eye. The number beside these sections represents the correction required for the vision of that particular eye.

Astigmatism is a common eye condition where the cornea (the outer layer of the eye) or the lens has an irregular shape, causing blurry or distorted vision. It's like having a rugby ball-shaped (oval) eye instead of a spherical one, which can make objects appear blurry at any distance. Eyeglasses, contact lenses, or surgery can often correct astigmatism and improve vision.

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How To Read an Eyeglasses Prescription

How to Read an Eyeglasses Prescription

Q: What is the legal blindness prescription?

If you have a prescription of -2.5 or lower, you will be considered legally blind in the UK. A prescription of -2.5 is equal to 20/200 vision. But in case the vision can be improved with glasses or contact lenses, it won’t be considered as a blind prescription.

Q: What does BVD mean in eye prescription?

"BVD" in an eye prescription stands for "Back Vertex Distance," indicating the space between the back of corrective lenses and the eye's cornea or spectacle plane. It’s usually mentioned in high-strength prescriptions.

Your go-to glossary to decode the jargon

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Glasses Prescription, Simplified

Knowing how to read an eye prescription is crucial because it empowers you to take control of your vision, ensuring that your glasses or sunglasses are tailored to your unique needs. This is why we're here to help.

But first, get your eyes tested comprehensively by our expert optometrists.

Book a free eye test

However, reading an eye prescription can be puzzling for many people. Let’s simplify the puzzle:
“How to read a prescription?”

How to Read a Glasses Prescription:

Sphere (SPH):

The SPH denotes the power of your glasses. It can tell you if you're short-sighted (“-” negative sign before the power, difficulty seeing distant objects) or long-sighted (“+” positive sign before the power, difficulty seeing closer objects).

Cylinder (CYL):

The cylinder in your prescription refers to astigmatism, a common irregularity in the shape of the eye. It measures the degree of this irregularity. Think of your eyes as ideally spherical, like a basketball. However, many eyes are more like a rugby ball, slightly oval shaped. The cylinder value indicates how much this shape deviates from being perfectly round.

A higher cylinder value suggests your eyes are more oval shaped, affecting your vision. If there s a 0 or nothing mentioned in this section, your eyes have a near perfect spherical shape.

Axis:

The axis complements the cylinder and denotes the orientation or angle of the irregularity caused by astigmatism.

It s measured in degrees from 0 to 180 and specifies the exact location of this imperfection in your eyes. This helps the optician precisely correct your vision.

Prism:

The prism in your prescription corrects eye alignment issues, such as double vision due to eye misalignment.

The prism power, direction (BU = base up; BD = base down; BI = base in; BO = base out), and strength help in aligning your eyes to eliminate visual disturbances.

Add:

The Add refers to additional power, mainly for reading, often associated with age related long sightedness (presbyopia).

As we age, it becomes harder to focus on close up objects. This positive number represents the strength of additional power required for clear near vision.

Pupillary Distance:

Your pupillary distance (PD) is the measurement between the centres of your pupils. This measurement is crucial for placing the optical centres of your lenses correctly.

While often measured by an optician, in some cases, you might need to measure it yourself to ensure the best vision experience with your glasses.

FAQs

What is the legal blindness prescription?

If you have a prescription of 2.5 or lower, you will be considered legally blind in the UK. A prescription of 2.5 is equal to 20/200 vision. But in case the vision can be improved with glasses or contact lenses, it won’t be considered as a blind prescription.

What is a normal axis for the eyes?

The eye axis refers to the location of astigmatism on the cornea, measured between 0 and 180 degrees. A normal eye axis typically indicates no significant astigmatism or a minimal level below 0.50 diopters. Astigmatism above 1.5 diopters usually requires corrective eyewear, while a measurement of zero diopters suggests the absence of this refractive error.

What does BVD mean in eye prescription?

“BVD” in an eye prescription stands for Black Vertex Distance, indicating the space between the back of corrective lenses and the eyes cornea or spectacle plane. It’s usually mentioned in high strength prescriptions.