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K.J. Ciuffreda, A. Selenow, B. Wang, G. Zikos, S.R. Ali, B. Vasudevan; "Bothersome" Blur: A New Functional Unit of Blur Perception . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2930.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Conventional measures of blur perception (e.g., depth–of–focus) are pure neurosensory threshold phenomena. However, the amount of blur perceived subjectively as being "bothersome", namely undesirable with respect to presumed task performance such as resolving fine target details and reading, remains unknown. Methods: A Badal optical system was used to measure blur detection (from far point target clarity to first slight blur), bothersome blur (increased blur that might adversely affect some task), and non–resolvable blur (further increased blur that would make the target non–identifiable) dioptric thresholds monocularly either to an isolated 20/50 or 20/200 Snellen E, or to 20/50 lines of text (8 deg), tested in consecutive order. The ascending method of limits was used. Blur values were referenced to the far point. Subjects were comprised of 13 visually–normal young adults. Cycloplegia was used to paralyze accommodation. A subset of subjects was also assessed over the course of a month, day, and hour to determine short– and long–term repeatability. Results: Within each target type, the mean bothersome blur threshold was always significantly larger than for blur detection and significantly smaller than for non–resolvable blur. Across target types and blur criteria, the bothersome blur thresholds for the isolated 20/50 E (1.02D) and the 20/50 text (1.34D) were not significantly different (p<0.10), although in 12 of the 13 subjects the latter were larger. However, both were significantly smaller than for the isolated 20/200 E (1.80D). These findings were repeatable over the three time courses tested. Conclusions: We have developed a new unit of functional blur termed "bothersome blur". It is primarily influenced by target detail, and secondarily by target extent. The trend for most values of bothersome blur to be larger for the 20/50 text rather than the single 20/50 letter suggests partial cone pooling of the blur information. These findings have important clinical implications with respect to tolerances for optical lens design and refractive surgery outcomes, as well as provide insight into basic aspects of human blur perception.
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