| Purpose. Although the foveal blur detection threshold has been well investigated, knowledge regarding the foveal blur discrimination threshold is limited. This study was conducted to determine the values of, as well as the relationship between, these two parameters.
Methods. A Badal optometer system was used to assess psychophysically both the blur discrimination and the blur detection thresholds at the fovea with accommodation paralyzed.
Results. The blur detection threshold was found to be 0.87±0.18D. The subsequent blur discrimination thresholds were relatively constant and significantly smaller than the blur detection threshold, with an average value of 0.48D±0.006D.
Conclusions. We speculate that the difference in magnitude between these two thresholds may be attributed to the defocus-related change in the ocular MTF, and its interaction with contrast discrimination ability, as well as the presence of a neuroperceptual blur buffering mechanism. The clinical implications will be discussed with regard to refractive and near-point testing.
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