Accurate corneal power measurements for IOL calculations

Outcomes following cataract surgery with greater than 90% of patients within 0.5 D of the target spheroequivalent refraction are achieved by less than 1% of surgeons. I give these surgeons an “A” for their results, just like in school. “B” surgeons are 80% to 89%, “C” surgeons from 70% to 79%, “D” surgeons from 60% to 69%, and if you are less than 60%, you are failing. An “A” surgeon uses optical biometry and re-measures axial lengths, usually with immersion, if the eyes differ by more than 0.3 mm or have a poor signal-to-noise ratio; uses a five-variable predictor IOL formula, such as Holladay 2, Olsen 2 or Barrett 2; continually personalizes his lens constant; and measures corneal power using the protocol described below.The first rule in good keratometry is no contact (IOP measurement) and no eye drops (even saline or artificial tears) before taking corneal measurements. Artificial tears or saline drops may generate a reading more easily in a dry eye, but the eye drops often cause steepening and punctate epithelial keratitis, which reduces the accuracy of the measurement. Blinking is much better than saline or artificial tears and is what the patient does normally. The patient should be asked to blink frequently while preparing for the measurement (alignment) and then stop blinking about 1 second before the measurement for the tear film to stabilize. If the patient is found to have dry eye, this must be treated before reliable keratometry is possible. Applanation pressure measurements flatten the cornea centrally and should not be performed before keratometry.