Base curve is one of the most critical parameters for contact lens comfort and safety. Understanding it helps you serve customers better and reduce returns.

What Is Base Curve?

Base curve (BC) is the curvature of the back surface of a contact lens. It determines how the lens fits on your cornea.

Measurement

• Unit: Millimeters (mm)
• Range: Typically 8.3mm to 9.0mm for soft lenses
• Principle: Smaller number = steeper curve, Larger number = flatter curve

Why Base Curve Matters

Too Steep (BC too small)

• Lens fits too tightly
• Reduced oxygen flow to cornea
• Lens does not move enough
• Discomfort, redness
• Potential corneal swelling

Too Flat (BC too large)

• Lens fits too loosely
• Excessive lens movement
• Lens may fall out
• Poor vision stability
• Edge awareness (feeling lens edge)

Standard Base Curves

Base Curve	Fit Type	Suitable For
8.3-8.4mm	Steep	Steeper corneas, Asian eyes
8.5-8.6mm	Medium-Steep	Most common, universal fit
8.7-8.8mm	Medium-Flat	Flatter corneas, larger eyes
8.9-9.0mm	Flat	Very flat corneas (less common)

How to Determine Customer Base Curve

Method 1: Professional Eye Exam (Recommended)

An optometrist uses a keratometer to measure corneal curvature precisely. This is the most accurate method.

Method 2: Trial and Error

If professional measurement is not available:

1. Start with 8.6mm (most universal)
2. Assess comfort after 4-8 hours of wear
3. If uncomfortable, try 8.5mm or 8.7mm
4. Document what works for future orders

Method 3: Previous Lens Parameters

If customer has worn contacts before, check their current lens packaging for BC value.

Regional Base Curve Preferences

Southeast Asia

Common: 8.5-8.6mm

Generally steeper corneas, smaller eye size.

East Asia (Korea, Japan, China)

Common: 8.5-8.7mm

Wide range, 8.6mm is most popular.

Middle East / GCC

Common: 8.6-8.7mm

Slightly flatter on average.

Europe

Common: 8.6-8.8mm

More variation, 8.7mm common.

North America

Common: 8.7-8.8mm

Generally flatter corneas.

Base Curve and Diameter Relationship

Base curve works together with diameter (DIA) to determine fit:

• Same BC, Larger DIA: Lens fits tighter
• Same BC, Smaller DIA: Lens fits looser

Example: A lens with 8.6mm BC and 14.5mm DIA will fit tighter than 8.6mm BC and 14.0mm DIA.

Common Base Curve Mistakes

❌ Ignoring Base Curve

BC is not optional. Wrong BC causes discomfort and potential eye health issues.

❌ Assuming One Size Fits All

While 8.6mm works for many, 20-30% of customers need different BC.

❌ Confusing BC with Diameter

BC = curvature, DIA = size. They are different parameters.

For Brand Owners: Inventory Planning

Starter Brand

• Offer 8.6mm only (covers ~70% of population)
• Note BC clearly on product pages
• Provide fit guidance

Growth Brand

• Offer 8.5mm and 8.7mm options
• Covers ~90% of population
• Reduces returns from fit issues

Premium Brand

• Offer 8.4mm, 8.6mm, 8.8mm
• Maximum fit coverage
• Professional positioning

Customer Education Tips

Help customers understand:

• BC is on their prescription or current lens box
• Wrong BC causes discomfort (not just color preference)
• If unsure, start with 8.6mm
• First-time wearers should consult an optometrist

At MIOMI Optical

We offer flexible base curve options:

• Standard: 8.6mm (most popular)
• Optional: 8.5mm, 8.7mm, 8.8mm
• Custom: 8.3-9.0mm range (MOQ applies)
• Documentation: BC clearly labeled on all packaging

Contact us: eye@miomi.cc | miomicon.com