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What does the base curve number mean?

Hi. My question is regarding the contact lens base curve number. The lenses I usually wear have a base curve of 8.5. However, I wonder if it is possible to buy a contact lens with a base curve 8.7? And does that mean it would look smaller/bigger than my pupil?

Note: the lenses I want to buy are cosmetic (coloured) lenses and everything suits my prescription apart from the base curve number.

Thanks in advance.

Optician’s answer

A base curve measurement represents how curved your contact lens is. This measurement affects how a contact lens sits on the front surface of your eye, and is quite important. Changing this value, even by a small amount, can cause blurred vision and discomfort if it’s not suitable for you.

If you’re thinking of changing lens type (e.g. from a clear to coloured contact lens) you will need to have a contact lens fitting with your optician. They will make sure that it’s the right fit for you, even if all the other numbers on your prescription match those of the new lens.

There are a number of factors that your optician will take into consideration and discuss with you before deciding whether a contact lens is suitable for you. Your contact lens material, wearing schedules and contact lens care may all factor into this.

Coloured contact lenses normally have a fixed aperture that you see through. This measurement is not the same as the base curve. If it is larger or smaller than your pupil size, your vision will be disturbed. Your optician will carry out checks to make sure that the contact lens is suitable for you in terms of the base curve and aperture before prescribing the lens.