To the Editor.
—In the article published in the Archives by Hoffer, it is stated that "the use of another ultrasound unit (Sonometrics DBR) and Binkhorst's formula is the least clinically accurate method." This statement is false.First, the accuracy of the Sonometrics Digital Biometric Ruler has been duly established in a study of aphakic eyes in which the axial length was measured as well as calculated.1 In this study, the accuracy of the Sonometrics DBR was shown to be 0.12 mm. For no other ultrasound unit has the accuracy been established in this manner thus far.Hoffer claimed that the Binkhorst formula was incorrect because it calculated IOL powers consistently 0.50-D stronger than other theoretic formulas. This is not true. The Binkhorst formula uses 0.25 mm for the thickness of the retina. Rather, it calculates slightly lower IOL powers than, for example, the Colenbrander formula, without retinal thickness,
Binkhorst RD. A Review of the Sonometrics DBR Unit and the Binkhorst Formula. Arch Ophthalmol. 1982;100(10):1680. doi:10.1001/archopht.1982.01030040654024
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