Abstract
To Editor. —In article published in theArchivesby Hoffer, it is stated that the use of another ultrasound unit (Sonometrics DBR) and Binkhorst's formula is least clinically accurate method. This statement is false. First, accuracy of Sonometrics Digital Biometric Ruler has been duly established in a study of aphakic eyes in which axial length was measured as well as calculated. 1 In this study, accuracy of Sonometrics DBR was shown to be 0.12 mm. For no other ultrasound unit has accuracy been established in this manner thus far. Hoffer claimed that 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 thickness of retina. Rather, it calculates slightly lower IOL powers than, for example, Colenbrander formula, without retinal thickness,
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