Contact Lens Guide: What Do B.C., DIA, G.DIA, and More Mean?

Contact lens specifications can feel confusing, especially if you are new to contact lenses. This guide explains commonly used contact lens terms in a clear and easy-to-understand way, so you can choose lenses that feel comfortable and suit your vision needs.

• What Is B.C. (Base Curve) in Contact Lenses?

B.C. (Base Curve) refers to the curvature of a contact lens. It should closely match the natural curve of your eye to help ensure a comfortable fit.
If the base curve does not suit your eye, you may experience discomfort or excessive lens movement, often referred to as the hula phenomenon.

• A smaller B.C. may feel tight and cause pressure on the eye.
• A larger B.C. may move more than expected and feel less stable.

Knowing your base curve can be helpful when selecting contact lenses. In most cases, a difference of about 0.1 does not result in a noticeable difference in comfort.

• What Does DIA (Diameter) Mean?

DIA (Diameter) refers to the overall diameter of the contact lens, including the transparent outer area.
Most contact lenses have a diameter of around 14.0 mm. Generally, a smaller number means a smaller lens size, while a larger number indicates a larger fit.

• What Is G.DIA (Graphic Diameter)?

G.DIA (Graphic Diameter) refers to the diameter of the colored or patterned area of a contact lens, excluding the transparent outer portion.
A larger graphic diameter creates a more defined eye appearance, while a smaller graphic diameter offers a more natural look. Preferred graphic diameter may vary depending on eye shape and pupil size.

• What Is Water Content in Contact Lenses?

Water content indicates the percentage of moisture contained within the contact lens material.

• One-day lenses generally have higher water content than monthly lenses.
• HEMA lenses usually contain a higher level of moisture.
• Silicone hydrogel lenses typically have lower water content but allow more oxygen to reach the eyes.

• Understanding Contact Lens Power (PWR / SPH)

PWR (Power) or SPH (Sphere) refers to the prescription strength of the contact lens used to correct vision.

• Minus (–) values are used for nearsightedness (myopia).
• Plus (+) values are used for farsightedness (hyperopia).

• Contact Lens Material & Functional Types

Contact lenses are made from different materials and functional features to enhance comfort, eye health, and visual experience.

• HEMA (Hydroxyethyl Methacrylate)
  Provides high water content and a soft, flexible feel. Designed for comfortable wear, especially in short to medium durations.
• Silicone Hydrogel
  Offers high oxygen permeability, allowing more oxygen to reach the eyes. Suitable for longer wearing times and maintaining eye health.
• MPC (2-Methacryloyloxyethyl Phosphorylcholine)
  A hydrophilic polymer that enhances moisture retention and reduces protein deposits. Helps maintain lens comfort throughout the day.
• PC (Phosphorylcholine)
  Mimics the natural surface of the eye to improve wettability and reduce friction. Supports long-lasting comfort and healthy lens wear.
• Blue Light Blocking Contact Lenses
  Designed to help reduce exposure to blue light from digital screens. Ideal for users who spend long periods on computers, tablets, or smartphones.

• Replacement Schedule for Contact Lenses

The replacement schedule indicates how often contact lenses should be replaced.

• One-day (Daily)
  Designed for single-use wear and disposed of after each day. Offers excellent hygiene and convenience, with no cleaning or storage required.
• Monthly
  Designed for daily wear for up to one month with proper cleaning and storage. Balances comfort, practicality, and cost-effectiveness.
• Long-term Wear (6 Months – 1 Year)
  Designed for extended use over six months to one year, depending on the product. Requires consistent and thorough lens care to maintain comfort and eye health.

Following the recommended replacement schedule helps maintain comfort, hygiene, and overall eye health.