Contact lenses offer a popular and effective way to correct vision for many people. While the prescription strength is often top of mind, another measurement, the “base curve,” plays an equally important role in ensuring comfortable and healthy contact lens wear. Understanding this specific curvature and its significance is important for anyone considering or currently using contact lenses.
Understanding Base Curve
The base curve (BC) refers to the curvature of the back surface of a contact lens. This specific measurement is designed to align with the unique curvature of the wearer’s cornea, which is the clear, dome-shaped front part of the eye. Base curve values are typically measured in millimeters, with common ranges for soft contact lenses falling between 8.3mm and 9.0mm; an average base curve is around 8.6mm. A smaller base curve number indicates a steeper curvature, while a larger number signifies a flatter curve.
Why Base Curve is Crucial for Contact Lens Fit
The correct base curve ensures the contact lens sits properly on the eye. A well-fitting lens allows for appropriate movement with each blink, which is necessary for tear exchange beneath the lens. This tear exchange helps to flush away debris and supply oxygen to the cornea, which is vital for its health and transparency. A properly fitted base curve also contributes to overall comfort, making the lens feel almost imperceptible during wear. It supports clear vision by keeping the lens centered and stable on the eye, preventing blurry or fluctuating sight.
Consequences of an Incorrect Base Curve
Wearing contact lenses with an incorrect base curve can lead to problems. If a lens is too “flat,” it may move excessively, causing discomfort, a feeling of something in the eye, fluctuating vision, or increasing the risk of debris getting trapped under the lens, potentially leading to irritation or abrasions. Conversely, a lens that is too “steep” will fit too tightly. A tight fit can restrict tear movement, reducing oxygen supply to the cornea and potentially causing swelling, redness, and discomfort. Prolonged oxygen deprivation can lead to serious conditions like corneal edema or the growth of new blood vessels into the cornea, which can compromise vision.
How Your Base Curve is Determined
Determining the correct base curve requires a comprehensive eye examination by an eye care professional, as individuals cannot accurately measure their own. During the examination, specialized instruments like a keratometer or corneal topographer are used to precisely measure the curvature of your cornea. This measurement provides a starting point for selecting the appropriate base curve. Following this, the eye care professional will typically conduct a trial fitting, observing how the selected lens moves and sits on your eye to ensure optimal comfort, vision, and eye health. Different contact lens brands or types may have slightly different base curves, necessitating specific prescriptions for each type of lens.