Details about Value of Keratometry Readings

K-reading

All what u need to know about k readings

K1


  • Kf ( k flat )
  • Curvature power of the flat meridian of the anterior surface of the cornea
  • measured within the 3-mm central zone
  • expressed in diopters (D).
  • Normal K1 is > 34 D.

In myopic correction

  • each –1 D correction reduces flat K by 0.75 D to 0.8 D.
  • Final flat K should be > 34 D to avoid spherical aberrations with bad vision quality even with post-treatment zero refraction

K1 should be calculated using the axial curvature method rather than tangential one.

K2


  • Ks ( k steep)
  • Curvature power of the steep meridian of the anterior surface of the cornea
  • measured within the 3-mm central zone
  • expressed in diopters (D).
  • Normal K2 is < 49 D.

In hyperopic correction

  • Each +1 D correction will add 1.2 D to steep K.
  • Final steep K should be < 49 D to avoid spherical aberrations with bad vision quality even with post-treatment zero refraction

K2 should be calculated using the axial curvature method rather than tangential one.

KM


  • K-average
  • Mean curvature power of the anterior surface of the cornea
  • Measured within the 3-mm central zone
  • Expressed in diopters (D).
  • Considered to avoid flap complications.
  • Km is should be > 40 D to avoid free-flap
  • Km should be < 46 D to avoid button-hole complication.

Kmax


  • Maximum curvature power of the whole anterior surface of the cornea
  • Expressed in diopters (D)
  • Normal Kmax is < 49 D
  • The normal difference in Kmax between the two eyes is < 2 D
  • The normal (Kmax-K2) difference in the same eye is < 1 D.
  • Whenever the difference between kmax and K2 is ≥ 1D, K-max should be used instead of K2 for Hyperopic correction to avoid spherical aberrations with bad vision quality even with post-treatment zero refraction

 K-max should calculated using the axial curvature method rather than tangential one.

Topographic astigmatism (TA)


  • The difference between K2 – K1
  • Within the 3-mm central zone
  • TA should be compared with the manifest astigmatism (MA).
Articles by : Dr. Reda Gomah