Many people know they need a prescription from an optometrist to purchase eyeglasses. However, few understand why their eyeglasses prescription is different from their contact lens prescriptions. Many incorrectly assume there is one universal prescription that fits all. While different brands of eyeglasses lenses can use the same prescription, contact lens prescriptions are different as every lens fits differently on the eye. Each soft contact lens comes with two other parameters, the base curve and the lens diameter. The base curve dictates how flat or steep the lens sits on the eye. Our corneas are different. Some patients might have flat corneas, others might have steeper ones. Depending on your corneal curvature, the lens with the right base curve for you is chosen. Furthermore, to a smaller degree of variability lenses will have different diameters as dictated by the manufacture of each brand.
Can contact lenses correct for astigmatism?
Yes, contact lenses can correct for astigmatism. However that’s another reason why contact lens prescription and glasses prescription are often different. Pre-made soft contact lenses are usually available in half diopter intervals and only start at 0.75. With base eyeglasses prescriptions that don’t fit around those restrictions, your optometrist would have to determine what’s best to convert it to. Your eye doctor might often need to trial on your eyes lenses with different parameters to determine a final contact lens prescription.
Can I use one contact lens prescriptions for different brands?
Unlike eyeglasses, different contact lenses could potentially have different prescriptions for the same person at one point in time. Part of the reason is that different lenses will have different curvatures, sizes and material. The level of how steep or flat a lens is can affect the power of the lens and therefore different contact lenses could have different prescriptions if they are different.
Furthermore, often times soft lenses aren’t suitable for certain eyes and therefore your optometrist will need to fit you with custom rigid gas permeable lenses (RGP) or scleral lenses to correct vision. These are highly customizable lenses created for each individual patient according to their precise eye shape and parameters. For those custom contact lenses the prescription will be significantly different that your spectacle’s prescription.
Can contact lenses affect the health of my eyes?
When being fitted for contact lenses it’s imperative to assess the health of the eye to ensure that it is safe for the patient to wear contact lenses in general and if they are candidates for a specific lens. For example patients with mild dry eyes might be more suitable for certain contact lenses than others. Other conditions such as keratitis precludes patients from wearing any contact lenses altogether until the condition is managed and resolved. Contact lenses with reduced oxygen permeability and water content can also exacerbate certain conditions. For the safety of your eyes, it is important to speak to your optometrist for consultations on contact lenses for what’s best for your eyes before attempting to wear any lenses.