Contact Lens Base Curve (BC) Explained Simply

What Is Base Curve (BC)?

The base curve (BC) is the inner curvature of a contact lens, measured in millimeters (mm). It determines how well the lens fits your eye’s shape.

• Smaller BC (e.g., 8.4mm) = Steeper curve (fits tighter)

• Larger BC (e.g., 8.6mm) = Flatter curve (fits looser)

Why Does BC Matter?

A proper BC ensures:
✔ Comfort – No irritation or dryness
✔ Stability – Lens stays centered on your eye
✔ Clear Vision – Prevents blurriness from lens movement
✔ Oxygen Flow – Lets your cornea breathe

Why Is 8.6mm the Standard?

• Most people’s corneas match an 8.4mm–8.8mm curvature.

• 8.6mm is the middle ground, fitting ~90% of wearers comfortably.

• Brands like Unibling use 8.6mm BC for universal fit & safety.

Can I Wear a Different BC?

❌ No! A wrong BC causes:

• Too Tight (Small BC) → Redness, poor oxygen flow

• Too Loose (Large BC) → Lens slides, blurry vision
  👉 Always check your optometrist’s prescription!

Does a Larger BC = More Comfort?

Myth! Comfort depends on your eye’s natural shape, not just BC size.

• Flat corneas → Need larger BC (e.g., 8.8mm)

• Steep corneas → Need smaller BC (e.g., 8.4mm)

How to Find Your Perfect BC?

1. Get a professional eye exam (corneal topography helps).

2. Stick to your prescribed BC—don’t self-adjust!

3. Choose trusted brands (like Unibling) with tested 8.6mm BC lenses.