Contact Lens Diameter: What is the Right Size?

Contact Lens Size: “Diameter” Meaning

Every valid contact lens prescription for contact lenses includes the following: 

Without the diameter measurement of a contact lens, your contact lens seller will have to deem your contact lens Rx as “invalid”. 

The diameter of a contact lens is the edge-to-edge measurement of a contact lens. 

Infographic drawing explaining the diameter of a contact lens.

Disposable soft contacts from the top brands (Acuvue, Alcon, Bausch & Lomb, and Coopervision) have the diameters of their contacts predefined and, therefore, are not adjustable. 

With other styles and brands of contact lenses, the diameter plays a critical role in the fit of a contact lens.

Diameter Explained (Video)

Lens Diameter Ranges

The cornea is that clear dome over the iris (the colored portion of your eye that gives a person their “eye color”). A soft contact lens sits on top of the cornea and covers it. 

The average cornea is about 12 millimeters from edge to edge, so a contact lens must at least be 12 millimeters. 

The goal of a soft contact lens is to cover the cornea completely and stretch an extra 1 millimeter around the entire circumference of the cornea. 

Therefore, if the cornea is 12mm and you must add 1mm on each side to account for the entire both sides, then a contact should be around 14mm (12mm + 1mm + 1mm). 

Diameter for lenses generally ranges from 14.0mm to 14.5mm. However, in the four top brands of disposable contacts, there is only one diameter size available, which your eye doctor will be able to work into your prescription.

How to Know the Right Contact Diameter Size

The average contact lens diameter size is around 14mm, given that the average cornea is about 12mm in diameter.

If you have smaller eyes, you may be closer to the 14mm diameter size, whereas big eyes may land more towards the 14.5mm end of the range. However, it’s important to note that the diameter must  work alongside the other contact measurements, such as the base curve.

If your eye doctor recognizes that a contact lens is not fitting properly, they may adjust the diameter and/or the base curve to create the correct fit.

What if My Lens Diameter is the Wrong Size?

Diameter is very important to the fit of a contact lens. If the diameter is incorrect in a contact lens prescription, the contacts may fit too loose or too tight. This can cause discomfort, irritation, or more serious eye health issues.

In recent years, the top brand companies that manufacture contact lenses have started predetermining their diameters based on calculations, testing, and lens design before their product even hits the market. The difficulty of choosing a diameter by your doctor has been negated. 

However, many doctors are still fitting rigid gas permeable contacts and other specialty type lenses where the determination of the diameter is critical to the fit. Therefore, since a contact lens diameter is not always predetermined, it is simpler to request that all prescriptions must include the lens diameter.

What does DeliverContacts.com do to ensure that I have the correct Diameter?

We make sure that every prescription we receive has all the necessary details included in the script, including the Diameter. 

Some products that we carry are limited in diameter selection, but we ensure that you have the ability to specify your diameter at the time of order. This way, you can ensure that your order with us aligns with your correct prescription.

Frequently Asked Questions (FAQs)

What does “lens diameter” on contact prescriptions mean?

The diameter of a contact lens is the edge-to-edge measurement of a contact lens.

What sizes do contact lenses come in?

Diameter for lenses generally ranges from 14.0mm to 14.5mm. However, in the four top brands of disposable contacts, there is only one diameter size available, which your eye doctor will be able to work into your prescription.

Is diameter size for contacts important?

Diameter is very important to the fit of a contact lens. If the diameter is incorrect in a contact lens prescription, the contacts may fit too loose or too tight. This can cause discomfort, irritation, or more serious eye health issues.

What if my lens diameter is too small?

If the diameter of a lens is too small, then the contact lens will tend to slide around too much. The contact lens will fit loose and be uncomfortable. 

If a doctor recognizes that the lens diameter is creating a loose fit, to compensate they may either enlarge the diameter to tighten the fit or reduce the base curve (which steepens the contact lens) to tighten the fit.

What if my lens diameter is too big?

A lens that is too big tends to irritate the eye by limiting the contact lens movement and tear flow on the cornea. The contact lens diameter will fit too tight and be uncomfortable. 

If a doctor recognizes that a diameter is creating a tight fit, they may compensate by shortening the diameter to loosen the fit or increase the base curve (which flattens the contact lens) to loosen the fit.

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