In keratoconus, the Amsler-Krumeich grading system classifies Grade IV keratoconus as:

• A Central K-readings 48-54 D, central corneal thickness 400-500 μm, no scarring
• B Eccentric steepening only, refraction > -8.00 D sphere or -4.00 D cylinder
• C Central K-readings > 55 D, central corneal thickness < 200 μm, or central corneal scarring ✓
• D K-readings > 48 D, pachymetry 300-400 μm, no Vogt's striae

Explanation

The Amsler-Krumeich keratoconus grading has four stages: Grade I (eccentric steepening, K < 48 D, no scarring, thickness > 500 μm); Grade II (K 48-53 D, no scarring, thickness 400-499 μm, refraction changes); Grade III (K 53-55 D, no central scarring, thickness 300-399 μm); Grade IV (K > 55 D, thickness < 200 μm, or any central corneal scarring). Grade IV represents end-stage keratoconus where corneal cross-linking (CXL) is contraindicated (pachymetry < 400 μm at the thinnest point is a relative contraindication due to risk of endothelial damage from UV-A exposure), and penetrating or deep anterior lamellar keratoplasty (DALK) becomes necessary.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.