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To the Editor:
—I fear I did not make my point sufficiently clear, as I did not wish to be too outspoken. I am not by any means "of the opinion that no instrument save the eikonometer is useful in measuring" aniseikonia, or "ocular imagery," as Captain Field prefers to call it (a better device has long been in use at the Dartmouth Eye Institute), but I was attempting to show that the data given were unscientific. Imagine trying to measure 1 per cent with an instrument on which the subject could not detect 5 or 10 or (in some cases) even 20 per cent; think of expecting a patient to detect a difference of 1/50 inch (0.5 mm.) at 15 feet (457 cm.) and try to conceive of an ophthalmologist's advocating an instrument for measurement of heterophoria which showed systematically a tendency to convergence on his looking into the machine, as the