What Is Base Curve In Contact Lenses? 

If you’re new to wearing contact lenses, it can feel overwhelming getting to know the different aspects that make up your prescription. From learning the correct cleaning process to understanding the hygiene standards you’ll need to adhere to when inserting the contacts themselves – it can seem like a whirlwind of information to come to terms with. 

Though your optometrist will be able to determine which lenses are best suited to you, it’s important to know when a contact lens doesn’t fit well to your eye, as this could lead to damage of the eye and future health problems, too. The base curve is vital to the comfort of your contacts, so here’s some more information on its impact.

What Is The Base Curve? 

The base curve is an important aspect of a lens, being the curvature on the surface of the back of the contact. The base curve is what determines the kind of fit the lens needs to have in order to match your eye’s natural curve. A base curve will vary from person to person, with those possessing a higher base curve figure having a flatter cornea (the clear outer layer at the front of the eye) and those with a lower number indicating a steeper cornea. 

A base curve value is typically conveyed in millimetres; however, it can also be categorised as being steep, median or flat. The average base curve value will range between 8.0 and 10.0mm, although the number may be flatter as a result of having a rigid gas-permeable lens. 

base curve

Does The Base Curve Have An Impact On Comfort?

The reason it’s so important to have regular appointments with your optometrist is because the right kind of contact lens will differ from person to person. Having the correct lens that fits your eye is vital in not only ensuring your vision is clear, but also that you’re comfortable when wearing your contacts, too. The base curve, alongside the lens’s diameter, play a vital role in establishing which kind of fit you need to help correct your poor vision. The diameter of a contact lens refers to its width from edge to edge, defining where the lens will sit when in your eye. 

Also measured in millimetres, the diameter of a contact lens is generally between 13mm and 15mm, though for rigid gas-permeable lenses, this number can often be as small as 9mm. The diameter of a lens is important, as it determines whether or not you’re going to be comfortable when wearing your contacts (if it’s in the correct position) or uncomfortable (where it can cause discomfort and even fall out, due to being unable to hold its position on your eye).   

Both the base curve and the diameter of a contact lens, when correct, will ensure a comfortable fitting lens, providing full coverage of the cornea and optimum edge alignment. The base curve and diameter can even affect the movement of the lens for tear exchange, which refers to the flow of the tears at the edge of the lens, triggered each time we blink. This tear exchange helps to clear out any debris or fragments from our eyes. A lens that is well fitted to the eye will also prevent dryness from occurring, as the cornea will be appropriately covered – dryness can be a regular occurrence for those with badly fitted lenses, causing a lot of discomfort and irritation to the eyes. Another benefit of the correct base curve is that it reduces the chances of edge strain, where the lens tightens, which can result in further discomfort and even cause damage to the eye, in some cases. 

Should I Be Asking For Lenses With An Alternative Base Curve? 

You should never wear contact lenses that have a different base curve from the one in your prescription, as your prescription has been specifically designed for you based on the measurements and health of your eyes – which is different for everyone.

Wearing lenses that have an alternative base curve from your prescription can cause damage to both your eyes and your vision. This should be considered when buying cosmetic contact lenses, for example, coloured lenses for fancy dress, as these are often a standardised size, and not suitable for all wearers. 

Should I Be Asking For Lenses With An Alternative Diameter? 

Like the base curve, you should not be wearing contact lenses that have a different diameter from your prescription. This is because a diameter too small for your eye will cause a tight, uncomfortable fit, and a diameter too wide will result in the lens slipping out of the eye altogether. If you’re concerned about the diameter, or the base curve of your contact lenses, speak to an eye health professional for more advice on your prescription.