Expert offers pearls on measuring corneal power
KOLOA, Hawaii — Cataract surgery outcomes can improve by a full diopter by correctly measuring corneal power, according to a speaker here.
At Hawaiian Eye 2017, Jack T. Holladay, MD, MSEE, FACS, discussed how to get the best results by practicing the correct keratometry procedure, beginning with avoiding any type of eye drops before taking a reading.
Jack T. Holladay
“That drop of saline or artificial tear will increase the power of the cornea because of epithelial edema, as much as 0.5 D,” he said. “Those K readings aren’t any good.”
Secondly, measuring IOP should be avoided because the cornea will be “flattened with applanation tonometry,” lasting between 30 minutes and an hour.
Patients should be instructed to blink repeatedly directly before the keratometry reading is taken, Holladay added.
While keratometry will be accurate most of the time, in the case of irregular astigmatism, topography or tomography should be used.
“If the standard deviation of the K reading [is] more than 0.2 D, then you should walk that patient over to the topographer and mark that thousands of points to determine what that power is,” Holladay said.
Keratometers measure four to 24 points on a ring, whereas topographers measure thousands of points in a zone, he said.
Any patient with an irregular astigmatism with 30 µm of deviation should also be flagged for topography,he said.
“Thousands of points will get you a much better measurement,” Holladay said. – by Rebecca L. Forand
Holladay J. Measuring corneal power: When should I use keratometry, topography or tomography. Presented at: Hawaiian Eye; Jan. 14-20, 2017; Koloa, Hawaii.
Disclosure: Holladay reports he has financial interests or relationships with Abbott Medical Optics, AcuFocus, Alcon Laboratories, ArcScan, Calhoun Vision, Carl Zeiss, Elenza, Oculus and Visiometrics.