Thinking about contacts but unsure how your prescription changes? It’s a common question! Many people wonder if their glasses prescription directly translates to contact lenses, and it can feel a bit confusing at first.
Don’t worry, it’s simpler than you might think to figure out the differences. We’ll break down everything you need to know about contact lens prescription vs glasses in a way that’s easy to follow, so you can make the best choice for your vision. Let’s get started so you can see clearly, no matter which you choose.
Contact Lens Prescription Vs Glasses Prescription What’s The Difference
When you get your eyes checked, you receive a prescription. This prescription tells your eye doctor what power is needed to correct your vision. You might be used to seeing this for glasses, but if you’re considering contact lenses, you might notice that the prescription looks a little different.
This is because glasses sit on your face, a specific distance away from your eyes, while contact lenses sit directly on the surface of your eye. This fundamental difference means the way your vision is corrected needs to be adjusted. Understanding these adjustments is key to getting the right fit and the clearest vision with contacts.
Why Your Prescriptions Aren’t Always The Same
The main reason a contact lens prescription differs from a glasses prescription is the position of the lens relative to your eye. Glasses are worn a short distance from your eyes, on the bridge of your nose. This distance is factored into the calculations for your glasses prescription.
Contact lenses, on the other hand, sit directly on your cornea. This proximity means that the way light enters your eye is slightly different, and therefore, the power needed to achieve clear vision can also be different.
Spherical Power The Basics
The spherical power, often written as ‘Sphere’ or ‘SPH’ on your prescription, is the most common part of your vision correction. It corrects nearsightedness (myopia) and farsightedness (hyperopia). For someone with simple myopia or hyperopia, the spherical power might be very similar between their glasses and contact lens prescription.
If you are very nearsighted, you’ll have a minus (-) number. If you are farsighted, you’ll have a plus (+) number. A higher number means a stronger lens.
For example, if your glasses prescription says SPH -3.00, it means you need three diopters of correction for nearsightedness. Your contact lens prescription might also be -3.00 for the spherical component. However, as we’ll see, other factors can come into play.
Cylindrical Power Astigmatism Correction
If you have astigmatism, your eye’s shape isn’t perfectly round, but more like a football. This causes blurry or distorted vision at all distances. Your prescription will include a ‘Cylinder’ or ‘CYL’ value and an ‘Axis’ value.
- Cylinder (CYL): This indicates the amount of astigmatism you have. It will always have a minus (-) sign.
- Axis: This indicates the direction or orientation of your astigmatism. It’s measured in degrees from 0 to 180.
When you switch from glasses to contacts, the cylinder and axis values for astigmatism correction often change. This is because glasses sit away from the eye, and the lenses are designed to account for this. Contact lenses, sitting directly on the eye, need a different type of correction for astigmatism, especially for moderate to high amounts.
Toric contact lenses are specifically designed to correct astigmatism and have different parameters than standard spherical lenses.
Base Curve And Diameter Key Contact Lens Measurements
While your glasses prescription focuses on the optical power needed, your contact lens prescription includes additional measurements essential for fit and comfort. These are not typically found on a glasses prescription.
- Base Curve (BC): This measurement describes the curvature of the back surface of the contact lens. It needs to match the curvature of your cornea for the lens to sit comfortably and correctly on your eye. A flatter cornea needs a flatter base curve (higher number), while a steeper cornea needs a steeper base curve (lower number).
- Diameter (DIA): This is the overall width of the contact lens, measured from edge to edge. The diameter is important for ensuring the lens covers the correct portion of your cornea and moves appropriately with your eye.
These measurements are determined by your eye doctor during a contact lens fitting. They are critical for ensuring the lenses stay in place, provide good vision, and are comfortable to wear throughout the day.
When Your Rx Might Be The Same
For some people with very mild vision correction needs, especially those with only slight nearsightedness or farsightedness and no astigmatism, their glasses prescription and contact lens prescription might be very similar, or even identical, in terms of the spherical power. If you have a simple prescription like SPH -1.00 and no astigmatism or other complexities, you might find that a -1.00 contact lens works perfectly. However, even in these cases, the base curve and diameter will still be specific contact lens measurements.
When Your Rx Will Likely Differ
Your prescriptions are most likely to differ significantly if you have:
- Astigmatism: As discussed, the cylinder and axis values require specialized toric contact lenses, and their specifications will differ from your glasses.
- High Prescriptions: For very strong nearsightedness or farsightedness, the power adjustments needed for contact lenses can be more pronounced.
- Specific Eye Conditions: Certain eye conditions might require special types of contact lenses where the prescription parameters are unique.
Your eye doctor will perform specific tests during a contact lens fitting to determine the exact parameters needed for your contact lenses. This ensures optimal vision and comfort.
The Importance Of A Contact Lens Fitting
This is where the real difference in getting a contact lens prescription comes in. Simply taking your glasses prescription to the store and buying contacts will not work and can be harmful to your eyes. A contact lens fitting is a crucial step.
Your eye doctor will:
- Measure the curvature of your eyes (base curve).
- Measure the size of your pupils and corneas (diameter).
- Assess how your eyes move and blink.
- Trial fit different types and brands of contact lenses to find the best match for comfort, vision, and eye health.
- Check how the lenses fit and move on your eyes.
This fitting process ensures that the contact lenses you wear are safe, comfortable, and provide the best possible vision. It’s not just about the numbers; it’s about how the lens interacts with your unique eye.
Can I Use My Glasses Prescription For Contacts
No, you cannot directly use your glasses prescription to buy contact lenses. While the spherical power might be the same in some cases, the essential measurements for base curve and diameter, and often the cylinder and axis for astigmatism, are unique to contact lenses. Attempting to use a glasses prescription for contacts can lead to ill-fitting lenses, discomfort, blurry vision, and potentially serious eye health issues like infections or corneal damage.
Always get a professional contact lens fitting.
How To Get A Contact Lens Prescription
Getting a contact lens prescription involves a standard eye exam followed by a specialized contact lens fitting. Here’s the general process:
- Schedule an Eye Exam: Book an appointment with an optometrist or ophthalmologist. Inform them that you are interested in contact lenses.
- Comprehensive Eye Exam: The doctor will check your vision, eye health, and discuss your visual needs and lifestyle.
- Contact Lens Fitting: This is an additional part of the exam. The doctor will use specialized equipment to measure your eyes precisely for contact lenses. They will then have you try on diagnostic lenses.
- Lens Evaluation: The doctor will assess the fit, comfort, and vision with the trial lenses. Adjustments may be made.
- Prescription Issuance: Once the doctor determines the correct lens parameters for you, they will write you a contact lens prescription. This prescription will include the base curve, diameter, power, and any necessary cylinder and axis information.
- Purchase Contacts: With your valid contact lens prescription, you can then purchase your lenses from an eye care provider or an approved online retailer.
Comparing Specs With A Table
To make the differences clear, let’s look at a typical glasses prescription versus what you might see on a contact lens prescription.
| Measurement | Glasses Prescription | Contact Lens Prescription |
|---|---|---|
| OD (Right Eye) Sphere | -2.50 | -2.50 |
| OS (Left Eye) Sphere | -2.75 | -2.75 |
| OD (Right Eye) Cylinder | -1.00 | -0.75 |
| OS (Left Eye) Cylinder | -1.25 | -1.00 |
| OD (Right Eye) Axis | 180 | 175 |
| OS (Left Eye) Axis | 5 | 10 |
| Base Curve (BC) | Not applicable | 8.6 |
| Diameter (DIA) | Not applicable | 14.2 |
In this example, the spherical power is the same for both eyes. However, the cylinder and axis values are slightly different for the contact lenses, reflecting the need for precise astigmatism correction with a lens that sits directly on the eye. The base curve and diameter are measurements that are exclusively for the contact lenses.
Different Types Of Contact Lenses
The type of contact lens you choose will also influence your prescription and the fitting process.
- Soft Contact Lenses: These are the most common type, made from flexible plastic and water. They are comfortable and easy to wear. They come in daily disposable, two-week, and monthly options.
- Rigid Gas Permeable (RGP) Lenses: These lenses are firmer and offer very crisp vision, especially for those with significant astigmatism or certain eye conditions. They require a longer adaptation period but can provide excellent clarity.
- Toric Contact Lenses: Specifically designed for people with astigmatism. They have different powers in different meridians to correct the distorted vision.
- Multifocal/Bifocal Contact Lenses: For people who need correction for both near and far vision (presbyopia), these lenses have different zones for different distances.
- Specialty Contact Lenses: This includes lenses for conditions like keratoconus, or cosmetic lenses for changing eye color.
Your eye doctor will recommend the best type of lens for your vision needs, eye health, and lifestyle during the fitting.
Common Pitfalls To Avoid
There are a few common mistakes people make when thinking about contact lens prescription vs glasses. Being aware of these can save you trouble.
- Assuming they are the same: The most significant pitfall is thinking your glasses prescription is all you need for contacts.
- Buying from unverified sources: Always ensure you are purchasing contacts with a valid prescription from a reputable seller.
- Not attending a fitting: Skipping the fitting appointment is risky and can lead to eye damage.
- Sharing lenses: Contact lenses are medical devices prescribed for an individual and should never be shared.
- Wearing damaged lenses: If your lenses tear or become damaged, discard them immediately and use a fresh pair.
Frequently Asked Questions
Question: Can I order contact lenses online with my glasses prescription
Answer: No, you cannot order contact lenses online using only your glasses prescription. You need a specific contact lens prescription, which is issued after a professional contact lens fitting by an eye doctor.
Question: How much does a contact lens fitting cost
Answer: The cost of a contact lens fitting varies by location and the eye doctor’s practice. It is typically an additional fee on top of a standard eye exam. Many insurance plans offer some coverage for contact lens fittings and supplies.
Question: How long is a contact lens prescription valid
Answer: Contact lens prescriptions are typically valid for one year, similar to glasses prescriptions. However, your eye doctor will determine the validity period based on your eye health and vision stability.
Question: What if my eyes are very sensitive
Answer: If your eyes are very sensitive, it is even more important to have a thorough contact lens fitting. Your eye doctor can help you find specialized lenses made from materials that are more breathable and comfortable for sensitive eyes.
Question: Can I wear my contact lenses if they feel uncomfortable
Answer: If your contact lenses feel uncomfortable, you should remove them immediately and consult your eye doctor. Discomfort can be a sign of an ill-fitting lens, a problem with the lens material, or an underlying eye issue.
Final Thoughts
Transitioning from glasses to contact lenses involves more than just a simple number swap. The way glasses and contacts interact with your eyes is fundamentally different, leading to distinct prescription requirements. While the core power for nearsightedness or farsightedness might appear similar, the crucial measurements for base curve, diameter, and precise astigmatism correction are unique to contact lenses.
These specific parameters, determined during a professional fitting, ensure not only clear vision but also the comfort and safety of your eyes. Never attempt to use your glasses prescription for purchasing contact lenses, as this can lead to discomfort, poor vision, and potential harm to your eyes. Always seek out a qualified eye care professional for a contact lens fitting to get the right prescription and the best possible visual experience.
Your eye health is paramount, and a proper fitting is the cornerstone of safe and effective contact lens wear.
