understanding your optical prescription – Catwalk Eyewear




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Understanding Your Prescription

understanding your optical prescription

If you've ever been prescribed medication, it can be confusing to understand what you're taking and why. This blog post will explore the basics of prescription medications and dispel some common myths about them. 

We'll also provide some tips on how to manage your prescriptions best. By the end of this post, you should have a better understanding of your medications and how they can help you.

What Is An Optical Prescription?

An optical prescription is a document provided by an eye care professional that contains all the necessary information to fill a person’s eyeglass or contact lens prescription. The written prescription includes important details such as the type and strength of lenses needed and any special instructions for fitting or using the lenses.

Most prescriptions will also include a line for the patient’s name, date of birth, and the doctor’s signature. Sometimes, the prescription may include additional notes about the patient’s vision or health history.

How Is it Measured?

An optical prescription is a set of numbers representing the strength of the lenses your eyes need to see clearly. These numbers are measured in diopters, indicating the amount of correction your lenses need to provide to improve your vision.

Three main components are measured in an optical prescription:

  1. The sphere power indicates the amount of correction needed for nearsightedness or farsightedness. A plus (+) sign indicates a need for correction for nearsightedness, while a minus (-) sign indicates a need for correction for farsightedness.
  2. The cylinder power indicates the amount of correction needed for astigmatism. This value is always a number without a plus or minus sign.
  3. The axis indicates the orientation of the astigmatism correction. This value is given as a number between 0 and 180 degrees, with 90 degrees considered straight up and down.

What Do The Numbers On An Optical Prescription Mean?

There are a few different types of numbers that you may see on your optical prescription, and each number corresponds to a different measurement. Here is a breakdown of the most common numbers that you may see:

-Sphere (SPH): This number indicates how much correction is needed for nearsightedness or farsightedness. A positive number means you are nearsighted, and a negative number means you are farsighted.

-Cylinder (CYL): This number indicates the astigmatism present. A higher number means more correction is needed.

-Axis: This number corresponds to the angle of astigmatism. It is usually between 1 and 180, with 90 being the most common axis.

How To Read An Optical Prescription

If you've never had an eye exam or it's been a while since your last one, the optometrist or ophthalmologist who prescribes your glasses or contact lenses will likely review your prescription with you. They'll explain what the numbers and symbols on your prescription mean. But, in case you don't have time for that during your appointment or if you want to know more about reading an optical prescription before your appointment, here's a brief guide:

The first thing you'll see on most prescriptions is the patient's name, date of birth, and exam date. The following section will list the type of refractive error that was diagnosed. Myopia (nearsightedness), hyperopia (farsightedness), presbyopia (age-related farsightedness), and astigmatism are the most common types of refractive error.

The following section lists the power of each lens to correct vision in each eye. The right eye is usually listed first, followed by the left eye. This is given in diopters (D). If there is no number listed next to an eye, it means no correction is needed for that eye. For example, +3.50-2.75 X 180 means that a myopic person would need a 3.50 diopter lens in their right eye and a 2.75 diopter lens in their left eye; someone with astigmatism.

What Are The Different Types Of Lenses?

There are four main types of lenses: single vision, bifocals, trifocals, and progressive lenses.

Single-vision lenses correct one field of vision, either distant or near. Bifocals have two distinct areas: the top part of the lens is for distance, and the bottom is for close. Trifocals have three distinct areas: the top part of the lens is for distance, the middle part is for intermediate range, and the bottom is for near. Progressive lenses gradually change power from top to bottom so you can see at all distances.

Understanding Your Prescription For Eyeglasses

Understanding your prescription can feel like a daunting task if you've never had to wear glasses before. But don't worry - we're here to help! This section will walk you through everything you need to know about reading and understanding your eyeglasses prescription.

First, let's start with the basics. Your eyeglasses prescription will include four pieces of information: your sphere (Sph), cylinder (Cyl), axis, and pupillary distance (PD).

Sphere (Sph): This measures the correction you need for nearsightedness or farsightedness. A plus sign (+) in front of the number means you are farsighted, while a minus sign (-) indicates nearsightedness.

Cylinder (Cyl): This measures the amount of correction you need for astigmatism. A positive number indicates that your cornea is more curved than average, while a negative number indicates that it's flatter.

Axis: This tells us where the cylindrical power is focused on your cornea. It's expressed as a number between 0° and 180°.

Pupillary Distance (PD): This is the distance between your pupils, and it's used to ensure that the centre of your lenses is aligned with your pupils. Your PD will be measured in millimetres (mm).

Add: If you need reading glasses, two other numbers in your prescription will correspond to the amount of correction needed for close-up work. One other number is for distance vision in one eye, while the other is for distance vision in the other.

Understanding Your Child's Glasses Prescription

Assuming you've read and understood the previous section on eye prescriptions, let's move on to understanding your child's glasses prescription. Like adult glasses, three main values make up a child's prescription: Sphere (SPH), Cylinder (CYL), and Axis.

The Sphere value is used to correct either nearsightedness or farsightedness and is represented by a minus (-) sign for nearsightedness or a plus (+) sign for farsightedness. The Cylinder value is used to correct astigmatism and is also represented by a minus (-) or plus (+) sign, depending on the type of correction needed. Finally, the Axis value is used to identify the location of the cylindrical power on the lens and is always given in numbers from 1-180.

Here is an example of what a child's prescription might look like:

OD: -1.00 -0.50 x 90

OS: -0.75 -0.25 x 10

This prescription indicates that the child has mild nearsightedness in both eyes that need to be corrected with negative spherical lenses. They also have a small amount of astigmatism in both eyes, which needs to be corrected with cylindrical lenses. The axis values tell us that astigmatism in the right eye (OD) is located at 90 degrees, while astigmatism in the left eye (OS) is located.


We hope this article has helped you understand your prescription medication better. If you have any questions, ask your doctor or pharmacist. And always read the label carefully before taking any medication.


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