When to Validate Your Findings.

For Keratometry
The measurements should be verified before acceptance if:

• The corneal power is less than 41.0 diopters, or greater than 47.0 diopters.
• If there has been prior keratorefractive surgery. In this case the corneal power will need to be estimated by the corresponding methodology, appropriate for the type of keratorefractive surgery performed.
• The average corneal power difference between the two eyes is greater than 0.09 diopter. Average corneal power = (K₁ + K₂)/2.
• The patient cannot adequately fixate, as seen with a mature cataract, macular hole, etc.
• The amount of corneal astigmatism by is greater than 2.50 D.
• The corneal diameter is less than 10.75 mm or greater than 13.0 mm.
• There is any problem with patient cooperation, or understanding.
• For a more complete listing of IOLMaster validation criteria, please refer to the IOLMastersection of this web site.

For the measurement of axial length, the measurements should be verified before acceptance, if...

A second person should re-measure both eyes if:

• The axial length is less than 21.30 mm, or greater than 26.60 mm in either eye.
• The axial length is greater than 26.0 mm, and there is a poor retinal spike, or wide variability in the readings. In this case, a B-scan should be scheduled to look for a peripapillary posterior staphyloma. At the same time, the axial length should be measured to the center of the macula by vector A-scan.
• There is a difference in axial length between the two eyes of greater than 0.33 mm that cannot be correlated with the patient's oldest refraction.
• Axial length measurements do not correlate with the patient's refractive error. In general, myopes should have eyes longer than 24.0 mm and hyperopes should have eyes shorter than 24.0 mm. Exceptions to this rule involve steep, or flat corneas. Be sure to use the oldest refractive data.
• There is difficulty obtaining correctly positioned, high, steeply rising echoes, or wide variability in individual axial length readings for either eye.
• There is any kind of problem with patient cooperation, or understanding.

For Intraocular Lens Power
A second person should repeat the axial length measurements, keratometry readings and re-run the IOL power calculations for both eyes if:

• The IOL power for emmetropia is greater than 3.00 diopters different than anticipated.
• There is a difference in IOL power of greater than 1.00 diopter between the two eyes.
• If the patient has had prior exicmer laser based keratorefractive surgery and the calculated IOL power for standard phacoemulsification is less than +17.0 D or greater than +23.0 D.

Reference: Knox-Cartwright NE, Johnston RL, Jaycock PD, Tole DM and Sparrow JM. The Cataract National Dataset electronic multicentre audit of 55,567 operations: When should IOLMaster biometric measurements be rechecked? Eye (2009), 1-7.