Contact Lens Prescription: How to Calculate It and Choose the Right Lenses for Comfortable Vision

Have you ever experienced dry eyes, irritation, or blurry vision while wearing contact lenses, even though the prescription matches your glasses? If so, you may be using the wrong type of prescription. This is because a contact lens prescription is not always the same as an eyeglass prescription.


In this article, Monde Eyewear explains the differences between contact lens prescriptions and eyeglass prescriptions in a simple and easy-to-understand way. We’ll also show you how contact lens powers are calculated so you can choose lenses that best suit your vision needs and lifestyle.


Key Takeaways

  • Contact lens prescriptions and eyeglass prescriptions are often different because contact lenses sit directly on the cornea, while eyeglass lenses are positioned several millimeters away from the eyes.
  • If you have a prescription of ±4.00 D or higher, your contact lens power will usually need to be adjusted from your eyeglass prescription.
  • In addition to lens power, selecting the right Base Curve (BC) and lens material can help reduce dryness, irritation, and discomfort during wear.


Table of Contents


Are Contact Lens Prescriptions the Same as Eyeglass Prescriptions?

Not always. Contact lens prescriptions and eyeglass prescriptions can differ, especially for people with moderate to high levels of nearsightedness or farsightedness, typically from ±4.00 diopters and above.


The reason lies in what eye care professionals call the vertex distance—the space between the corrective lens and the eye. Eyeglass lenses generally sit about 12 millimeters away from the cornea, while contact lenses rest directly on the eye’s surface.


Because contact lenses eliminate this distance, the effective optical power changes. As a result, the prescription often needs to be adjusted to ensure that light focuses accurately on the retina and provides the clearest, most comfortable vision possible.


What Contact Lens Powers Are Available?

Today, contact lens powers are measured in diopters (D) and are generally available in the following increments:

  • For myopia (nearsightedness) or hyperopia (farsightedness) up to ±6.00 D, lens powers typically increase or decrease in steps of 0.25 D, such as -1.75, -2.00, or -2.25.
  • For prescriptions above ±6.00 D, powers are commonly available in 0.50 D increments, such as -6.50, -7.00, or -7.50.
  • Astigmatism correction (Cylinder power) usually starts at -0.75 D and increases in 0.50 D increments, such as -0.75, -1.25, or -1.75. Toric lenses also include an Axis value ranging from 10° to 180°.


What Happens If You Choose the Wrong Contact Lens Prescription?

ค่าสายตาคอนแทคเลนส์ผิด

Wearing contact lenses with the wrong prescription or incorrect fitting parameters can negatively affect both your vision and eye health.

Common symptoms include:

  • Eye Strain: Your eyes must work harder to maintain focus, leading to visual fatigue and discomfort throughout the day.
  • Headaches: Over-corrected lenses may force the visual system to work harder than necessary, resulting in headaches and eye fatigue.
  • Blurry or Unstable Vision: You may experience blurred vision, double vision, or difficulty focusing, especially if you have uncorrected astigmatism and are wearing standard spherical lenses.
  • Irritation and Dry Eyes: Poorly fitted lenses can contribute to dryness, irritation, and discomfort. In some cases, they may cause minor corneal abrasions that make blinking uncomfortable.


Looking for a Monde Eyewear store near you? Find your nearest branch and receive professional eye care services from our experienced team.


How to Convert an Eyeglass Prescription into a Contact Lens Prescription

Eye care professionals use a calculation known as the Effective Lens Power Formula to convert eyeglass prescriptions into contact lens prescriptions.


If your prescription falls between -0.25 D and -3.75 D, you can generally use the same power for both glasses and contact lenses. However, stronger prescriptions usually require adjustment.


For Myopia (Nearsightedness)

If your eyeglass prescription is -4.00 D or stronger, the contact lens power will typically need to be reduced slightly. For example: Eyeglasses: -4.25 D → Contact Lenses: approximately -4.00 D Eyeglasses: -5.00 D → Contact Lenses: approximately -4.75 D This adjustment helps ensure that images focus correctly on the retina and prevents unnecessary eye strain.


For Myopia with Astigmatism

For people with both nearsightedness and astigmatism, the calculation becomes slightly more complex. If astigmatism is less than -0.75 D, eye care professionals may use a spherical equivalent calculation, combining part of the cylinder power with the spherical power. If astigmatism is -0.75 D or greater, a toric contact lens is generally recommended. These lenses are specifically designed to correct astigmatism and require the sphere power, cylinder power, and axis to be prescribed accurately.


What Factors Should You Consider When Buying Contact Lenses?

When choosing contact lenses, consider the following factors:

  • Frequency of Use: Choose a lens type that matches your lifestyle. Daily disposable lenses offer maximum convenience, hygiene, and reduced risk of infection. Monthly lenses may provide better value for those who wear contact lenses every day.
  • Base Curve (BC): The base curve should closely match the curvature of your cornea. A lens that is too tight may cause redness and discomfort. A lens that is too loose may move excessively and cause irritation.
  • Water Content and Oxygen Permeability: Different lens materials, such as Hydrogel and Silicone Hydrogel, provide different levels of oxygen transmission and moisture retention.

These factors directly affect all-day comfort and help reduce symptoms of dry eyes.


Find the Right Contact Lens Prescription with Expert Advice at Monde Eyewear

Understanding your correct contact lens prescription and learning how to choose lenses that suit your eyes can help you enjoy clearer vision while reducing the risk of long-term eye health complications.


Before purchasing contact lenses, it is always best to consult with an eye care professional.


At Monde Eyewear, we are committed to helping you achieve clear and comfortable vision. Our eye examination services are performed by trained specialists under the supervision of optometrists. We also offer innovative video consultation services, allowing customers to receive professional advice from an optometrist as part of their eyewear journey.


In addition, we offer frame-and-clear-lens packages starting from just 990 THB. Enjoy peace of mind with our BVAX Warranty, which includes a free lens replacement within one year if you experience discomfort. We also provide complimentary cleaning, adjustments, frame fitting, and replacement of screws and nose pads throughout the lifetime of your eyewear.


Visit a Monde Eyewear store near you or enjoy free nationwide delivery across Thailand with no minimum purchase required.


Contact Monde Eyewear


FAQs


Q: Do I need special contact lenses if I have astigmatism?

A: If your astigmatism is less than -0.75 D, standard contact lenses may be suitable depending on the recommendation of an eye care professional. However, if your astigmatism is -0.75 D or greater, toric contact lenses are generally recommended because they are specifically designed to maintain proper lens orientation and provide clearer, more stable vision.


Q: Can people with presbyopia wear contact lenses?

A: Yes. People with presbyopia can wear contact lenses. Options include multifocal contact lenses, which provide clear vision at near, intermediate, and distance ranges within a single lens, or monovision correction, depending on the recommendation of an optometrist.


References 

Back to blog

Related Products

1 25

Related Blogs

1 4