Contact Lens Prescription Vs Glasses Prescription: What’s The Difference?
If you have refractive errors like farsightedness and nearsightedness, your eye doctor can prescribe eyeglasses or contacts. The decision is largely based on personal preferences as both will correct your vision. Other factors can also come into play like your lifestyle, hobbies and activities. Contacts may be better for people who do physical activities like sports.
Did you know you can’t use the same prescription for eyeglasses and contact lenses. Why? Well, eyeglasses “sit” approximately 12mm from the eyes while contacts “sit” directly on the eyes, this means that contacts require different refraction testing based on the proximity. This disparity in distance makes a big difference for some prescriptions, hence the need for two different prescriptions and customization when fitting eyeglasses or contact lenses. Another factor is that contact lenses for astigmatic correction can rotate on your eyes depending on how it sits on your cornea. Any movement or rotation as you wear contact lenses will require a custom prescription in order your eyes maintain good vision while contact lenses are worn.
If you have glasses and want contacts, a contact lens fitting is needed to determine if you’re a good candidate, educate you about all the different contact lens types, determine your contact lens prescription and much more. Usually a comprehensive eye health exam and contact lens fitting is recommended to be done together if it has been awhile since your last check up. Those who are just interested in an eye health check up and an updated eyeglass prescription then a comprehensive eye health exam is only needed.
Below we’ll compare contact lens prescriptions and glasses prescriptions in regard to many factors from type to validity, prescription conversion, and more. Let’s get started.
Eye Prescriptions: Explained
What’s in a Glasses Prescription?
Your eyeglass prescription usually has three numbers abbreviated as S, C and Axis. Here’s an example of an astigmatism glasses prescription and what the numbers mean:
- S (Spherical) is a measurement of the degree of a refractive error i.e., nearsightedness or farsightedness
- C (Cylinder) is a measurement of your refractive error to correct astigmatism
- Axis is a measurement of the orientation of your refractive error to correct astigmatism
- ADD and Prism can be also included in the prescription if applicable. Add is a measurement for progressive/bi-focal/reading prescriptions. Prism is prescribed to help people with certain eye conditions such as diplopia or double vision.
| RX | SPHERE | CYLINDER | AXIS | PRISM | ADD |
|---|---|---|---|---|---|
| O.D | -3.00 | -1.00 | 100 | ||
| O.S | -3.75 | -0.75 | 90 |
It’s worth noting that the prescription has three numbers for each eye i.e., the left eye (OS or Oculus sinister) and the right eye (OD or Oculus dexter). Each abbreviation has a number (diopters) underneath representing the degree of vision correction required.
Diopters represent the focusing power of the lens. The number can have a plus sign or a minus sign. The plus sign means you are farsighted while the minus sign means you are nearsighted.
What’s in a Contact Lens Prescription?
Your contact lens prescription will also include spherical, cylinder, axis and have additional information. The most notable include:
- BC (Base Curve): This is a measure of the curvature of the surface of your contacts that best align with the shape of your cornea to help with comfort and fitting.
- DIA (Diameter): DIA represents the diameter size of the lens you need. This measurement works alongside BC to help with comfort and fitting.
- Lens brand: Contact lens prescriptions also state the brand since different lenses are made with different materials, oxygen permeability and modalities.
Types of Eyeglass Prescriptions
Eyeglass prescriptions are generally categorized based on the different types of refractive errors as this affects how light is focused on the eye (retina). Here are the main types of lenses and how their prescriptions differ:
1. Single Vision Lenses without Astigmatism
These types of eyeglass lenses are most common as they correct farsightedness and nearsightedness. A prescription for eyeglasses with single-vision lenses will specify the spherical power needed to fix these underlying refractive errors at a given distance.
2. Single Vision Lenses for Astigmatism
If you have astigmatism (your cornea isn’t perfectly spherical), you require toric lenses that can correct cylindrical and spherical power.
3. Multifocal Lenses (Bifocal & Trifocal)
Bifocal lenses are used by individuals who can’t see both near and far objects clearly, such as people with age-related farsightedness or presbyopia. The prescription for bifocal lenses will therefore specify the spherical, cylindrical and ADD power for the near and far sections.
Trifocal lenses are meant for people who need to see clearly at multiple distances, perfect for those who work on computers and read a lot. The prescription for trifocal lenses will include the power for all three distances: near, immediate, and far vision.
4. Progressive Lenses
Since progressive lenses offer a gradual transition from near vision to far vision and don’t have visible lines between different powers like bifocals, they require spherical, cylindrical and ADD powers. Progressive lenses are surfaced and computer generated to create a very custom prescription for all visual distances.
5. Photochromic or Sun Lenses
These types of lenses can be made for all prescription types; single vision, multifocal and progressives. Instead of a clear prescription lens, these lenses are tinted, polarized or photochromic to help protect you from UV exposure and shade your eyes from brightness and glare for optimal clarity.
It is important to visit an eye doctor to get the right prescription and shouldn’t be overlooked. Remember, the wrong prescription can mark the onset of other eye conditions such as eyestrain, poor vision and visual discomfort.
How to Get a Glasses Prescription
Getting a prescription is as easy as going for an eye exam which includes a simple discussion of your overall lifestyle and an eye assessment that checks for everything and uncovers the most effective and optical prescription for your unique eyes.
You can get a comprehensive eye exam and eyeglasses prescription with ease from renowned Optometrists at Kodak Lens Vision Centers in Toronto and the Greater Toronto Area. Book an appointment.
How Long Are Glasses Prescriptions Valid?
The validity of eyeglasses prescriptions will vary depending on factors like overall eye health and age. Generally, you should have a new prescription after every one or two years¹.
However, since there’s no fixed timeline, follow your Optometrist’s recommendation as they will have observed your eye health and understand your visual needs.
Contact Lens Prescriptions: Explained
Just as with eyeglasses, there are also various types of contact lenses and prescriptions, all addressing different visual needs as well as conditions. Let’s take a closer look.
Types of Contact Lens Prescriptions
Like glasses, there are different types of contact lenses designed to function/interact differently with your eyes. The difference is usually in the material, design, and lens parameters: edge design, thickness, and base curve. As a result, different types of contact lenses will require different prescriptions. Here are the main types and their respective prescription differences.
1. Soft Contact Lenses
These types include daily disposable lenses which tend to have more water content. Bi-weekly and monthly disposable contact lenses also fall under the soft contact lenses category and tend to have a slightly different material to withstand longer wear. Monthly disposable lenses are made using the most durable material of all soft contact lenses. Most soft contact lenses correct for spherical prescriptions, but some brands also have astigmatism correction.
2. Gas Permeable (GP) Lenses
Different types of GP lenses will contain different prescription information. RGP lenses, which are made from firmer materials (to allow oxygen to freely pass through and offer sharper/more stable vision), will have the lens brand information in the prescription. The same applies to hybrid lenses designed with a softer outer shell material to offer balanced comfort and clarity. These are custom made lenses and can accommodate all prescription types.
3. Specialty Contact Lenses
Since specialty contact lenses are meant to tackle specific eye conditions, they tend to require a detailed prescription, complex lens design, and custom parameters to ensure a perfect fit and the desired results. Ask your optometrist to learn more.
How to Get a Contact Lens Prescription
To ensure you get the right contact lens prescription for your vision, new wearers must do a comprehensive eye exam and contact lens fitting. Your Optometrist will perform an eye assessment and discuss your overall lifestyle and daily activities to help decide which contact lenses are best recommended for you.
Kodak Lens Vision Centres are renowned for their comprehensive eye exams and wide selection of contact lenses from different brands. Schedule a contact lens eye exam and get the best contact lens prices and excellent fitting services.
How Long Are Contact Lens Prescriptions Valid?
As per the AAO (American Academy of Ophthalmology), contact lens wearers need to have their eyes checked and prescription updated yearly². Since contact lenses are worn directly on your eye and limit oxygen, contacts can impact your eye health compared to eyeglasses. Prescriptions may change yearly depending on your visual development so it is recommended to get an eye check up every year to ensure your contact lens prescription is up to date and your eyes are healthy. A contact lens prescription is valid for 1 year.
Contact Lenses Pros and Cons
If you are wondering why you should choose contact lenses, here are the top pros and cons for your consideration:
Main Pros
- Contacts improve/correct vision without altering appearance
- They are perfect for persons who lead an active life, such as those who play sports or engage in other outdoor activities
- Wearers can adapt quickly to contacts. Easy to insert and remove.
- There are daily disposable, bi-weekly and monthly contacts (FDA-approved)³
- Contacts don’t fog up or easily get dirty compared to eyeglasses
Main Cons
- There is a risk of eye infections if they aren’t used properly and cleaned as directed because contact lens materials are susceptible to buildup⁴
- They can cause irritation among persons with sensitive or dry eyes
- Possibility of requiring more frequent eye exams or follow ups
- Contact lenses have a limited wearing time
Glasses Pros and Cons
If you are wondering why you should choose glasses, here are the top pros and cons for your consideration:
Main Pros
- Glasses are a quick and simple way to correct refractive errors
- There is less risk of infection since glasses don’t touch the eyes
- There are a wide variety of frame styles and lens options to choose from
- They can be made into sunglasses
Main Cons
- They aren’t ideal for those who play sports or engage in outdoor activities
- Lenses must be cleaned every so often as they can fog up and get dirty
- The best and stylish frames can be costly
- Glasses can affect/block peripheral vision due to the frame size
Can You Use Your Glasses Prescription for Contact Lenses?
Sorry, but we don’t recommend it! You should not use your eyeglass prescription to get contact lenses due to the difference in vertex distance when being tested by an optometrist. While both contacts and glasses will treat the same refractive error, different measurements and testing are conducted by the optometrist to help determine a custom eyeglasses or contact lens prescription. Overall, your vision may be impacted as a glasses prescription will not have the same powers for vision correction required to get the correct contacts and vice versa. An eyeglass prescription must be compensated and tested by the optometrist to finalize the most optical contact lens prescription you’re most comfortable with.
Final thoughts
Understanding the differences between contact lens and glasses prescriptions is key to maintaining optimal eye health. Both serve the same purpose of correcting vision, but they require different measurements due to the positioning of each visual solution. While glasses are convenient and low-maintenance, contact lenses offer freedom for those with active lifestyles. For either option, it’s important to get regular and comprehensive eye exams to ensure the prescriptions meet your vision needs. Whether you need contacts, glasses, or both, visiting a trusted provider like Kodak Lens Vision Centres ensures you get expert and personalized vision care.
Click here to book your eyeglasses or contact lens exam now. We offer excellence in visioncare, a wide variety of specialty contact lenses, and top eyeglass brands for you, your family and friends.