Noticeable, troublesome and objectionable limits of blur.

We investigated limits at which induced blur becomes noticeable, troublesome and objectionable. We used 15 cyclopleged subjects, a Badal optometer with lines of three high contrast letters as targets, 3-6 mm artificial pupils, and 0.0-0.7 logMAR letter sizes. For 0.0 logMAR size, mean "noticeable" blur limits were +/-0.33D, +/-0.30D and +/-0.28D at 3 mm, 4 mm and 6 mm, respectively, but increased by about 70% for 0.7 logMAR letters. All limits reduced by about 17% as pupil size increased from 3 mm to 6 mm. Letter size had a significant influence on all blur limits (1.6-2.1 times), but blur direction had no significant effect. Magnitudes of "troublesome" and 'objectionable" limits were 1.6-1.8 times and 2.1-2.5 times relative to "noticeable" limits, respectively. Our results suggest criteria for troublesome and objectionable blur are relatively unaffected by letter size.