Correction for empty-field myopia produces an appreciable improvement in contrast thresholds only for small (less han about 8 min arc) stimuli. The amount of improvement that can be expected varies with the magnitude of the observer’s myopia.
S. M. Luria, "Target size and correction for empty-field myopia," J. Opt. Soc. Am. 70, 1153-1154 (1980)