Anatomical Considerations
Potentially Adverse Effects

Keratometer Mire Distortion
Irregular astigmatism or apecal displacement may be indicated by distorted keratometry mires. Contact lens wear has been associated with alterations in corneal topography. These changes can be intentional such as in the case of orthokeratology. Preocular tear film abnormalities can also result in distorted keratometer mires.

The distortion of keratometry mires may be graded as shown above. Grade +1 shows only a minimal loss of mire regularity, whereas in grade +4 mire regularity and clarity is severely altered. In these instances, keratometry readings are very inaccurate.