Your eye doctor carries a variety of glasses, and when you’re running low on your contact lens supply, they are the ones you turn to. Although you need a vision prescription for both, the details of their respective prescriptions vary slightly.
Glasses and contact lenses interact differently with your eyes, which is why they have different prescriptions. A contact lens exam and fitting can help determine which type of contact lens is perfect for you.
The Basics of Your Vision Prescription
A finalized vision prescription marks the end of most people’s routine eye exams. This slip of paper includes the necessary parameters for correcting your vision with glasses, contacts, or both! Once you understand what these numbers mean, it becomes easier to follow changes in your vision.
Glasses and contact lens prescriptions include key measurements, but each serves a slightly different purpose based on how they interact with your eye.
From left to right, a prescription has the same basic parameters:
- The sphere (SPH) indicates the strength of the lens needed to correct your vision. A negative sign (–) signifies myopia (nearsightedness), while a positive (+) sign means hyperopia (farsightedness).
- The cylinder (CYL) and axis measure astigmatism, a condition where the curvature of your cornea causes blurry or distorted vision. If you don’t have an astigmatism, these columns remain blank.
- ADD may appear if you need multifocal lenses, which is common with presbyopia, offering an additional prescription for up-close tasks.
A Closer Look at Contact Lens Prescriptions
What separates a contact lens prescription is that, along with basic vision parameters that outline the strength of your prescription, contacts include specific measurements about the lens itself:
- Base curve (BC): This refers to the curve of the contact lens’ back surface to match the natural curve of your eye for a comfortable fit.
- Diameter (DIA): This refers to the width of the contact and helps verify that the lens properly covers your cornea for a snug fit.
- Material and brand: We specify this detail because not all contact lenses are created equally. Your eye’s shape, size, and health dictate which lenses suit you perfectly.
An annual contact lens fitting allows us to measure your eye’s shape and size to find the lens option that aligns perfectly with your visual needs and lifestyle.
Why Glasses & Contact Lens Prescriptions Differ
Beyond what’s included in each vision prescription, it’s normal for the final numbers to vary slightly between glasses and contacts. This is because the physical placement of each lens dramatically influences how it corrects your vision.
Distance Matters
The key difference in these numbers lies in where the corrective lens rests relative to your eye:
- Glasses rest comfortably on the bridge of your nose, about 12–14 mm away from your eyes. This distance affects how light refracts and focuses on the retina. Because of this, the lens power needed in glasses can be slightly different than in contact lenses — sometimes stronger, sometimes weaker — depending on whether you’re nearsighted or farsighted.
- Contact lenses rest directly on the eye’s surface, on your cornea, eliminating this distance. As a result, the optical power required in contact lenses is slightly weaker (though not always), particularly for higher prescriptions.
Wearing lenses with a prescription that’s too weak or too strong can lead to eye strain, headaches, and blurry vision. Therefore, it’s necessary to have separate prescriptions for each form of vision correction.
We don’t recommend substituting your contact lens prescription for eyeglasses, or vice versa.
Curve & Comfort
Contact lenses must fit snugly onto your eye. What makes them unique are the base curve and diameter measurements that confirm proper alignment with your eye’s surface.
When contacts fit properly, they align with your cornea and stay secure when you move or blink, reducing the risk of irritation or even falling out of your eye.
Glasses, by contrast, don’t require these specifics because they don’t come into direct contact with your eyes, however, they still benefit from proper alignment. Glasses that truly fit your face make a huge difference in the quality of your vision and overall comfort.
Different Functions & Features
There are several types of contact lenses, each accommodating varying visual needs, comfort, and lifestyles. Contact lens prescriptions may include product-specific recommendations for the material or brand.
The type of lenses you need can depend on whether you’re correcting for dry eye, astigmatism, or multifocal needs. Although there are different lenses and coating options for glasses, their prescriptions don’t require these details.
How Long Do Prescriptions Remain Valid?
While eyeglass prescriptions are valid for 1 year at our clinic, contact lens prescriptions also require an annual contact lens exam, which may include a fitting if needed. Regular exams help ensure your prescriptions remain accurate and your eyes stay healthy.
Annual visits verify if your eye health can continue supporting the lenses you’re wearing, or whether it’s time to switch to something different. Contact lenses can affect your corneas over time, so regular checkups help detect potential complications such as irritation, inflammation, or infections.
Even in a year, your eyes and vision can change more than you think. Using an expired contact lens prescription could lead to discomfort, improper correction, or even harm to your eyes.
Staying up to date on your routine eye exams is a simple and effective way to maintain good eye health and vision.
Proper Contact Lens Wear & Care
Given their comfort, hand-free wear, and natural vision correction, it’s no wonder contact lenses are as popular as they are. But they also require greater maintenance and care to keep your eyes healthy and your vision sharp.
The Importance of Proper Hygiene
Poor care routines can lead to issues like irritation, discomfort, or keratitis, a painful corneal infection. To avoid this, follow these essential practices diligently:
- Wash your hands: Before handling lenses, thoroughly wash and dry your hands to prevent transferring bacteria or dirt.
- Use lens-specific solutions: Do not use tap water or saliva to clean lenses. This can introduce harmful bacteria to your eyes. Always use the solution recommended by your optometrist.
- Discard as directed: Follow the replacement schedule for your lenses. Using monthly lenses beyond their intended lifespan, for instance, increases the risk of infection.
While glasses don’t require as much maintenance, they offer unparalleled convenience. You can slip them on or off with no worry about hygiene, and they’re a great backup if you’re giving your eyes a rest from contact lenses.
See Clearly with Comfort
Whether you prefer the look of bold glasses, hands-free vision correction with contact lenses, or a combination of both, each solution has its own advantages. With several contact lens types and a variety of lens options for glasses, the choice is up to you!
What does matter is the quality of your vision and the validity of your prescription. Your eyes work tirelessly; nurture them with the care they deserve. There’s no better way to do that than staying on top of your routine eye exams. Schedule an appointment with Dr. Bishop & Associates. Our team is here to recommend solutions tailored to your visual needs, preferences, and lifestyle.
