You are here:

Ophthalmology & Optometry/8.6 vs 8.7 BC Air Optic for Astigmatisim


I am requesting information on exactly what the base curve means, and how much of a difference is there between 8.6 and 8.7. My perscription for the air optic toric lens is 8.7 according to my contact box. I've been searching online for a better deal than I can get through my eye dr, as it is $150 for 6 months. I found contacts offered that would be $78 for six months, however their BC is noted as 8.6. I would like to be able to purchase lenses for less the $150, however, if I can't see through them I will have wasted $78.... What exactly does the BC affect regarding the lense fit?

Hi Montie,
The base curve is the radius of curvature, in millimeters, of the optical portion of the lens. It is often derived, and not used to compare across brands or models. It affects the fit of the lens, meaning the way it lays on the cornea and how it moves and rotates. You should discuss with your doctor the 'other' lens and see if she would fit you in it and check it in order to prescribe it as you can only purchase lenses legally with a prescription. You can purchase the prescribed lens anywhere.  Fitting toric lenses is sometimes a bit tricky and the 'numbers' don't always predict or guarantee an expected outcome. It isn't so much that the BC numbers are close or not as much as it is a different lens with other design differences that can change the way it 'fits' and therefore the way you see and feel with it.
Best to you,
Mitch Axelrod, OD

Ophthalmology & Optometry

All Answers

Answers by Expert:

Ask Experts


Mitchell Axelrod


I'm happy to answer questions about eye exam findings and procedures, glasses and contact lens types/prescriptions/problems. I can also answer questions about general eye conditions/diseases. I do not answer questions concerning surgical techniques/procedures. Please state your age or within a small range when asking questions, as it is often important.


Optometrist 19 yrs.

Doctor of Optometry, cum laude; Residency in Ocular Disease

©2017 All rights reserved.