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Radius & Diopter Converter
Convert between corneal radius of curvature (mm) and keratometry readings (diopters) using the standard keratometry index.
Keratometry Conversion Calculator
Radius of curvature ↔ Diopters conversion
About This Conversion
- Uses standard keratometry index of 1.3375 (337.5 constant)
- Average corneal radius: ~7.8 mm (≈43.25 D)
- Steeper cornea = smaller radius = higher diopters
- Flatter cornea = larger radius = lower diopters
Keratometry Reference
The Keratometry Index
The standard keratometry index of 1.3375 (constant 337.5) is used to convert between radius and diopters. This is a calibrated index, not the true corneal refractive index, designed to estimate total corneal power.
Normal Corneal Values
- • Average radius: 7.8 mm (range: 7.0-9.5 mm)
- • Average power: 43.25 D (range: 37.50-48.00 D)
- • Steeper cornea: smaller radius, higher diopters
- • Flatter cornea: larger radius, lower diopters
Clinical Applications
- • Contact lens base curve selection
- • IOL power calculations
- • Keratoconus monitoring
- • Orthokeratology fitting
- • Comparing different keratometer outputs
Quick Reference
| Radius (mm) | Power (D) | Description |
|---|---|---|
| 7.20 | 46.88 | Steep |
| 7.80 | 43.27 | Average |
| 8.40 | 40.18 | Flat |
| 9.00 | 37.50 | Very flat |