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4.5 Corneal irregular astigmatism index
Corneal irregular astigmatism index
This is the index that simply quantitates the data of the corneal irregular astigmatism
which cannot be found by ordinary keratometer measurements (K1, K2, and AX)
according the keratometory image. There are 2 indexes (KAI and KRI) as shown below,
and each of them shows the level of irregular astigmatism.
KAI (Kerato-Asymmetry Index)
One of the corneal irregular astigmatism indexes which shows asymmetry of the cornea.
This index is calculated from the discrepancy between the center of the approximate
ellipse of the keratometer measurement point and the XY alignment measurement point
equivalent to the corneal vertex position. The value increases for asymmetrical corneal
shape such as when a part of cornea protrudes like keratoconus.
KRI (Kerato-Regularity Index)
One of the corneal irregular astigmatism that indicates the regularity (irregularity) of the
cornea. This index is calculated from the discrepancy between the keratometer
measurement point and its approximate ellipse. The value increases when the corneal shape
is irregular such as eyes with corneal transplantation or CL-induced problems.
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