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To the Editor.
—I found it difficult to determine from Dr Hoffer's article the objective criteria for instrument evaluation that he used. There are four major parts to the ultrasonic measurement that affect the result—the instrument, the transducer and its application, the formula for calculation, and the precision or accuracy of the measurement system. Hoffer presented his preferences for instruments, transducers, and formulas without demonstrating objective comparisons with all other factors controlled.The implication is that examination with a lower-frequency, nonfocused transducer and caliper measurement from photographs is more accurate than using a higher-frequency, focused beam transducer with electronic interval calculation averaging. This perception is contrary to physical principles.Certainly the choice of a transducer stand off or eye cup is an option available to the user of any instrument and hardly merits favoring one instrument over another.It is disappointing that the Archives would support Hoffer's unsubstantiated endorsement
Coleman DJ. A Review of the Sonometrics DBR Unit and the Binkhorst Formula. Arch Ophthalmol. 1982;100(10):1680. doi:10.1001/archopht.1982.01030040654023