How Do I Know That My Contacts Fit? Part 3: Fitting Contact Lens Diameter
Though it may seem like contact lenses are all the same, one size does not fit all when it comes to contacts.
Understanding Contact Lens Fit
In the previous two posts we discussed how your optometrist will find the right prescription and fit for toric lenses and multifocal lenses. Today we’ll talk about contact lens diameter and why it matters to your prescription.
Simply put, contact lens diameter correlates to the diameter of your cornea. In order for your prescription to work effectively, your contact lenses need to sit at the correct place on your eye. A contact lens that fits properly will fit over the cornea perfectly.
If your lens isn’t wide enough, a portion of the light that enters your eye would be refracted only by your eye’s lens (without the help of the contact lens), while the rest of the light entering your eye, with the help of the contact lens, would be in focus. This results in blurred vision.
If the lens is too big for your cornea, it may move too much and feel awkward in your eye.
How Contact Lens Material Affects Fit
Sometimes different materials of contact lenses can also make a difference in the way the lens fits. When selecting your proper size, your optometrist should consider this, as well as the base curve, in addition to the measurement of the diameter of your cornea. After you’ve started wearing your lenses, your doctor can then use a biomicroscope to make sure your they’re fitting just right.
Soft contact lenses should move around a little bit—one to two millimeters—every time you blink. Gas permeable contacts may move even a little more than that. But in general, if your lenses are moving around a lot, ask your optometrist to check your fit. Even a slight difference in the diameter measurement (even less than a centimeter) can affect how your contact lens feels in your eye.
Wearing a contact lens that doesn’t fit is not only uncomfortable; it can affect your vision. If your lenses feel scratchy, uncomfortable, or if your vision isn’t clear through your lenses regularly, talk to your America’s Best optometrist about checking your lens fit.
