An eye prescription is a document containing measurements and parameters for vision correction. It serves as a blueprint for creating corrective lenses, whether for glasses or contact lenses. When reviewing an eye prescription, some individuals may notice the abbreviation “BC,” which can prompt questions about its meaning and purpose. Understanding this term is important for vision correction, as it relates directly to eye comfort and health.
Understanding the Base Curve
The abbreviation “BC” on an eye prescription stands for Base Curve. This refers to the curvature on the back surface of a contact lens. This curvature aims to closely match the natural curve of the cornea, the eye’s outermost layer. Base Curve values are measured in millimeters (mm), indicating the lens’s degree of curvature.
The Base Curve is exclusive to contact lens prescriptions. This measurement is not found on prescriptions for eyeglasses because glasses sit some distance from the eye, whereas contact lenses rest directly on the corneal surface.
Why Base Curve Matters for Contact Lenses
A properly fitted Base Curve is important for ensuring comfort, maintaining clear vision, and safeguarding eye health when wearing contact lenses. The fit of the contact lens directly impacts how it interacts with the delicate surface of the eye. An incorrect Base Curve can lead to issues affecting immediate comfort and long-term eye health.
If the Base Curve of a contact lens is too flat, the lens will fit too loosely on the eye. This can cause the lens to move excessively with each blink, resulting in discomfort, blurry or fluctuating vision, and potential irritation. Excessive movement can also increase friction on the corneal surface, leading to abrasions or damage.
Conversely, if the Base Curve is too steep, the contact lens will adhere too tightly to the eye. A tight fit restricts the natural flow of tears and limits oxygen permeability to the cornea. This can cause discomfort, redness, irritation, and increase the risk of eye infections or corneal swelling. A correct fit ensures the lens sits appropriately on the eye, allowing for adequate tear exchange and sufficient oxygen to reach the cornea.
How Base Curve is Measured and Applied
Eye care professionals determine the appropriate Base Curve during a comprehensive eye examination. They use specialized instruments to precisely measure the curvature of the cornea. A common device for this is a keratometer, which assesses corneal shape and steepness.
Beyond instrumental measurements, the eye doctor also considers the overall shape of the eye and may utilize trial contact lenses. These trial lenses allow the professional to observe how different Base Curves interact with the individual’s eye, enabling fine-tuning of the fit for optimal comfort and vision. This process ensures the chosen lens provides the best possible physiological fit.
Once the appropriate Base Curve is determined, this specific value is included on the contact lens prescription. It appears alongside other parameters, such as the lens power (for vision correction) and diameter. It is important to only wear contact lenses prescribed by a professional, with the correct Base Curve, to ensure comfort and protect eye health.