How to Read your Contact Lenses prescription?

Reading contact lenses prescription-min

Having a clear vision is tied to a proper understanding of your contact lens prescription.  However, understanding your prescription is quite difficult especially when you have no inkling of the language of eye care professionals. 

The burning question now becomes, how do you read and understand your contact lens prescription? In this article, we will guide you through the process and ensure you understand it even if you’re not in the medical field. 

Understanding the Basics of a Contact Lens Prescription

There is no way you can talk about prescription or eye care and forget the abbreviations – OD and OS. 

OD stands for ‘Oculus Dexter which refers to the right eye while ‘OS’ stands for Oculus Sinister which refers to the left eye. There is also OU which stands for ‘Oculus Uterque’ and meaning ‘Both Eyes’. 

These terms are likely to be found in your contact lens prescription. Some doctors have switched things up a little by using LE against OS for the left eye and RE against OD for the right eye.

While there are other concepts, we will look at them shortly. 

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The Role of an Optometrist in Prescribing Contact Lenses

Optometrists are trained professionals in the assessment and adequate care of the eyes. This set of professionals detects vision defects, abnormalities, and other eye diseases. Their roles involve: 

  • Eye Examination
  • Eye Diagnosis and 
  • Eye Treatment

The first thing your optometrist will do is to start with a comprehensive eye exam on your visit. The examinations help feed him or her with information concerning your general health. During the exam, the optometrist evaluates your visual acuity and your overall eye health. 

Certain tools exist and help in making the examination efficient and effective. You will always find the eye chart that helps in determining how well you can see objects at various distances. While the physical examination takes place, your optometrist still needs to evaluate your eye’s internal structure. This internal examination helps check for eye defects like glaucoma, cataracts, and many others. 

It is not unusual for your optometrist to engage you in a conversation after conducting your eye examination. The conversation provides the optometrist with information on the challenges and stress that your eyes go through daily. For those who work from home, there is always the issue of eye strain coming from staring for long hours at the computer screen. 

Once your optometrist is done assessing your eyes and asking the right questions. Next up is the prescription which contains information on the type and kind of glasses or lenses to use. Don’t forget the examinations conducted earlier. The examination provides details and numbers to ensure you get the right fitting for your prescription. 

Most duties of the optometrist don’t end at examination. It also stretches into guidance and selection of a frame. The reason for this assistance is to help you select the right type, and material and even advise you on the wearing schedules. 

Deciphering the Terminology on Your Prescription

Just like every industry has its languages which seem like jargon to others, eye health is not left out. The key to having a clear understanding of your contact lens prescription is understanding those terminologies. They may sound and look foreign, but they are the key to making informed decisions about your eye health. Let’s look at some of them

  1. Sphere (Sph)

Sphere is the lens power to help correct your vision. You will always find this number accompanied by either a positive or negative sign. The positive sign is for farsightedness and the negative is for nearsightedness. In some prescriptions, you will find both positive and negative signs meaning the far and near vision needs correction. 

  1. Cylinder (Cyl) and Axis

You will find the cylinder and axis when talks about astigmatism are in place. Astigmatism is a condition where your cornea or lens has an irregular shape. 

The cylinder shows the degree of astigmatism; in essence how much additional power is required for clear vision. The larger the number, the greater the astigmatism. If you don’t find a number attached to Cyl, then you don’t have astigmatism. 

Axis is also measured in degrees, and points to the location of astigmatism in the eye. If you have astigmatism, there will be numbers on both Cyl and Axis. The axis helps with correct alignment. 

  1. Addition (Add)

You will commonly find this term with people who have presbyopia. Presbyopia is an age-related eye condition. Add simply tells you that extra power (magnification) is added to the bottom of a progressive lens. It will help in reading or doing any close-up task. 

  1. Base Curve 

You will always find this Base Curve written as BC. It shows the curvature of your contact lens; and how well the lens fits your cornea. The entire duty of the BC is to ensure your comfort and help you maintain a visual performance. It is usually a number between 8 and 10. 

  1. Diameter (DIA)

Just like during mathematics lessons where diameter has to do with size, it is the same here. Diameter refers to the size of your contact lens. It is the measurement across the lens from one edge to another. A suitable and proper diameter covers your cornea without compromising your vision or causing any irritation. It is usually a number between 13 and 15.

  1. Refractive Power

You can also call it Power. It shows the overall strength of the lens you need for vision correction. Your power considers your eye defects – nearsightedness, farsightedness, and astigmatism; and then proceeds to provide you with a comprehensive prescription to address your needs. 

  1. Optical Center

Your optical center is what many refer to as the sweet spot of your lens where your vision is most accurate. Know that your optical center must align with your pupil for clear vision. 

  1. Prism and Base

Your prism correction comes to light when there is a need to address eye alignment issues like strabismus. While your prism values show the amount of deviation, your base shows the direction of the deviation. 

  1. Expiration Date

Who would believe that contact lenses have an expiration date? But they actually do. There is a period when they should no longer be used to maintain your eye health and ensure the lenses’ effectiveness. The expiration date is usually one or two years after fitting. 

  1. SV

SV stands for Single Vision and simply means that your lens only has one prescription. 

  1. PD

PD  stands for Pupillary distance and is measures the distance between your eye’s pupils.

  1. BF

BF stands for Bifocal lenses and has two areas of vision. The first which is located at the top of the lens is for seeing objects at a distance while the other located at the bottom is for seeing near objects. 

  1. TF

You guessed right, Trifocal lenses. Just like BF, it has three areas of vision. The top of the lens is for seeing things at a distance, the middle of the lens is for the intermediary, and the bottom of the lens is for seeing near objects. 

  1. PL

Some also refer to PL as PAL which stands for Progressive Lens. It works similarly to the lenses described above just that it helps with seeing things at multiple distances. It also has no separating lines for the different vision areas as BF and TF do. 

The Different Components of a Contact Lens Prescription

While we have discussed the different terminologies associated with contact lens prescription, let’s throw our focus now on the basic components of your contact lens prescription. 

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Power and Sphere in Contact Lens Prescription

While the power shows the strength of the contact lens needed to correct vision, the sphere which is a component of power shows the overall refractive power of the lens. Positive power and sphere correct farsightedness while negative ones correct nearsightedness where distant objects become blurry.  

Base Curve and Diameter Explained

Your base curve is measured in millimeters and it shows the curvature of your contact lens while the diameter also measured in millimeters shows the size of your contact lens (width). Your base curve and diameter speak to the comfort and compatibility of your contact lens. 

Understanding Cylinder and Axis for Astigmatism

The Cyl in your prescription shows the additional power needed to correct astigmatism. The axis is measured in degrees from 0 to 180 and it shows the direction where the astigmatism is to be corrected. Cylinder and Axis both speak to astigmatism and ensure the correction of distorted vision. 

How to Ensure the Correct Fit of Your Contact Lenses

To ensure you get the perfect fit for your contact lens, some factors need consideration such as: 

  1. Accurate measurements

Imagine what it would look like wearing lenses with the wrong measurements. Discomfort will be at the top of your complaint. To avoid such complaints, your optometrist must assess and take measurements of several parameters, for example, base curve and diameter. 

  1. Lens Material and Type

There are different types and materials of contact lenses. For the right choice, your optometrist needs to understand your lifestyle, sensitivity, and any underlying health conditions. 

While we discuss ‌ensuring your contact lenses fit, be aware it takes time for your eyes to adjust to your contact lens. 

Adjustments and Changes in Prescription Over Time

Know that it can take you about 10 to 12 days to fully adjust to your contact lenses. Your optometrist will definitely give you some instructions on how to care for and use your new contacts.

During your adjustment phase, you are bound to experience some side effects such as blurry vision. This blurriness results from dryness. Your optometrist will always give you eye drops to help with the dryness.

You may experience discomfort. You will find yourself blinking more than usual and in some cases even tearing up. What you can do is to remove them and then re-wet them before wearing them. 

You may also feel tired and this usually occurs when you have worn them for a very long time. 

There are also symptoms you experience and it is a signal that it’s time to change your prescription. During your checkups, your doctor will always run examinations to ensure that your prescription matches the changes your eyes have been through.

Factors that can lead to changes in your contact lens prescription include

  1. Aging

As you get older, your vision reduces. You may need additional reading or multifocal lenses to cope.

  1. Lifestyle

Some living and working conditions can bring changes to your vision. Imagine spending over 10 hours every day on screen. 

  1. Eye Health

Along the way, conditions like cataracts may occur. These eye health issues require changes to your contact lens prescription.

Common Misconceptions about Contact Lens Prescription

There is news and information out there about contact lenses. If not careful, the wrong ones can drown out the right ones, leaving you confused. 

A typical example of such information is that contact lenses are harmful to the eyes. You can call this unbalanced information because contact lenses become harmful only when you have no proper hygiene towards them.  

There’s another notion that you can use your eyeglass prescription for your contact lenses prescription. Like how, who brings these notions? Well, let’s discuss this closely.

Differences between Eyeglasses and Contact Lens Prescriptions

While your contact lens and eyeglass prescription serve the same purpose, they are not the same. Let’s talk about the differences

  1. Lens Power

Both prescriptions have Sph values but that of contact lens always comes with an adjustment. The lens goes into the eye requiring a measurement of the distance between your lens and eyes.

  1. Additional Measurements

In your contact lens prescription, you will find the base curve, diameter, etc which is great for the eye but you don’t see such measurements in your eyeglass prescription.

Bear in mind that you cannot convert your eyeglass prescription to a contact lens. The optometrist will need to consider factors like lens type, materials, and placement and they are not needed for eyeglasses.

Why You Can’t Buy Contact Lenses Without a Prescription

You can’t just walk into a store and purchase contact lenses for your eye condition without a prescription. You need a proper eye examination before anything. In the examination, the doctor will take measurements of a lot like curvature, size, and power. 

When you decide to purchase yourself, you may end up with the wrong one for you. This wrong one may cause discomfort, blurred vision, and in the worst cases – an eye infection. 

Therefore, you must go through an eye care professional before purchasing contact lenses. 

Tips for Managing and Maintaining Your Contact Lens Prescription

One way to have good eye health while using your contact lenses is proper management and maintenance. Here is how you can do so: 

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Keeping Track of Your Prescription Details

To avoid misplacement, you can save your prescription details on your Google Drive. The prescription details can come in handy, especially during emergencies.  

Don’t play with your check-ups. These check-ups play a huge role in your eye health. To help your memory, set reminders for your eye check-ups. 

In keeping a record of your prescription details, know the expiry date and ensure you change it early enough. While using and you notice changes, speak with an eye care professional immediately.

When to Seek Professional Help for Contact Lens Issues

Your new lenses are bound to cause you discomfort and even some teary eyes, especially in your first week. However, you need to know when to seek professional help and when the symptoms you experience are no longer normal. 

If you experience any of the following, reach out to an eye care professional immediately:

  1. Sudden vision changes
  2. Eye infection
  3. Torn lenses
  4. Continuous irritation and discomfort 
  5. Eye discharge


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