Contact lenses and glasses are the two most popular forms of vision correction for most people. They both provide clear vision by correcting refractive errors. However, the technology behind these lenses differs, and so will their prescriptions.
Contacts and glasses have unique vision prescriptions that aren’t interchangeable. Because of how they sit on the eye, there’s a slight discrepancy between the values.
Contacts sit directly on the eye’s surface, while glasses sit a few millimeters away from the eyes. This difference in placement means that the strength of the lenses has to be adjusted accordingly, hence the slight difference in prescription.
Understanding the Vision Prescription
The vision prescription lays out the roadmap to clear vision, but it can seem confusing at first glance. Let’s start by breaking down what these numbers illustrate.
A typical vision prescription includes several components.
From left to right, the first value is the Sphere (SPH). This indicates the lens power prescribed to correct myopia or hyperopia. The following number represents diopters (D), which increase by 0.25. A negative sign (-) refers to myopia, allowing you to see distant objects more clearly, while a positive sign (+) indicates hyperopia, improving your focus on nearby objects.
The next column is the Cylinder (CYL), which measures astigmatism resulting from an irregular cornea or lens curvature. The CYL value is usually negative, increases by 0.25 D, and is always paired with an axis value. A CYL value indicates the lens power necessary to balance the eye’s irregular curvature.
Not everyone has astigmatism. No CYL value indicates that no astigmatism correction is needed. Subsequently, this means there’s also no axis to your prescription.
The final number on a basic vision prescription is the axis. This is a number between 0 and 180 degrees that specifies the orientation of the astigmatism correction on the lens.
For those who require correction for presbyopia, there will be a final ADD value at the end of the prescription. This reflects the additional magnification for reading or other close-up work and is usually a positive value.
Occasionally, a vision prescription may include prism correction to help with binocular vision concerns like double vision. This value indicates the amount of prism correction needed, with a base direction (up, down, or outwards) outlining the prism’s orientation.
Interestingly, while the same base parameters (sphere, cylinder, axis, and add) are used in both glasses and contact lens prescriptions, their measurements often differ slightly. This is because of the distinct way each corrective method interacts with your eyes.
Why Contacts & Glasses Have Different Prescriptions
While the same basic parameters of a vision prescription are used in both contacts and glasses, their individual prescriptions aren’t interchangeable.
This is mainly because of the difference in how contacts and glasses correct vision and rest on the eyes.
Contact lenses sit directly on the cornea, requiring additional measurements such as a base curve and diameter to confirm that they fit properly and comfortably. In contrast, glasses sit a few millimeters away from the eyes.
The difference in placement means that the lenses’ strength must be adjusted accordingly.
For instance, consider someone with a glasses prescription of -3.25, -1.25 x 150. From left to right, this includes the sphere, cylinder, and axis. When we translate this to contact lenses, the prescription may adjust slightly due to their difference in proximity to the eye.
In our example, this may translate to a contact lens prescription of -3.00, -1.00 x 150. The prescription is slightly weaker to account for the lack of distance between the lens and the eye.
Therefore, your glasses prescription doesn’t necessarily translate to your contact lens prescription. Visiting your optometrist for your contact lens fitting helps determine the correct parameters of your contact lens and your contact lens prescription.
Using the parameters of your glasses prescription as your contact lens prescription isn’t ideal for your vision and ocular health. While the discrepancy may be small, it may lead to eye strain, headaches, and discomfort.
Contacts or Glasses: Which Is Better?
While the discrepancy between these prescriptions is very slight, it encourages a conversation (or longstanding debate) about which is better: glasses or contacts.
The answer isn’t cut and dry. Ultimately, this decision boils down to personal preference, comfort, and visual clarity each individual seeks.
Glasses
Some individuals prefer the convenience and fashion statement of glasses. You can select a sleek, minimal frame or choose something bold and unique. Others relish the freedom and unobstructed vision that contacts provide.
Glasses can offer a quick fix, shielding eyes from wind and debris. They provide a stable option with no direct eye contact, reducing the risk of irritation.
Contact Lenses
On the other hand, contacts offer a more natural field of vision as they move with the eye, eliminating distortions and reflections caused by glasses. However, they do require more daily care and maintenance to prevent the risk of irritation and infection.
Comfort is subjective.
Some find glasses heavy, while others can’t bear the thought of placing contacts on their eyes. Modern advances in both technologies have significantly enhanced comfort levels, making both options viable for a broad range of users.
When choosing your primary vision correction method, consider your lifestyle. Do you partake in sports or outdoor activities that might make glasses impractical? Or do you enjoy the fashion flexibility glasses offer? Understanding these personal factors can guide you to the right choice. Plus, you always have the freedom to choose both!
Say Hello to Clear, Comfortable Vision
Whether you prefer wearing glasses, contacts, or a combination of both, understanding the difference between these forms of vision correction is helpful.
Regardless of your preference, if you’d like to browse our selection of frames or schedule a contact lens fitting, visit our team at Orillia Optometry!
