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What is the appropriate gold standard test for refractive error?

The usefulness of clinical tests is often determined by assessments of their discriminative ability, repeatability and/or validity. The latter is often assessed by a comparison with a gold standard test: if the new test provides results similar to the gold standard, it will be regarded as providing valid results and vice-versa. Autorefractors are typically assessed by a comparison with results from subjective refraction, which is typically taken as the gold standard assessment of refractive error. In many respects, this seems an appropriate choice, but surprisingly the methodology of subjective refraction is rarely fully described in studies in the ophthalmic literature, even when it is being used as a gold standard. A common description is ‘monocular subjective refraction was performed based on subjective refinement of the autorefractor readings until bestcorrected visual acuity was achieved’. Indeed, the subjective refraction is often described in terms of producing Best Corrected Visual Acuity (BCVA; a misleading term and the focus of an earlier editorial).