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B. Wang, K. J. Ciuffreda, B. Vasudevan; A Conceptual Model of Human Blur Sensitivity. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1010.
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In previous laboratory studies, human blur detection (depth-of-focus; DOF) and blur discrimination (equiblur zone) thresholds were investigated in the foveal, near peripheral (≤8º), and far peripheral retina (up to 50º). Based on these findings, an empirically-derived, conceptual model of blur sensitivity to retinal defocus has been developed, with basic and clinical implications.
The relationship between blur perception and retinal defocus was quantified dioptrically in depth (0-5 D) at the fovea, as well as across the peripheral retina, in two- and three-dimensional visual space. Point-wise linear regression was performed to fit the observed data for both the blur detection thresholds and multiple blur discrimination thresholds across the near retinal periphery. Non-linear regression was used to characterize the DOF (zone of clarity) at the fovea, as well as across the retinal periphery up to 50º.
.The equiblur zones increased in proportion to the magnitude of the DOF in the near retinal periphery, with a ratio of approximately 0.6. Linear regression equations, y=0.61+0.09x and y=0.33+0.05x, were found to describe the blur detection thresholds and mean blur discrimination thresholds, respectively, at the fovea and across the near retinal periphery. An exponential curve described the DOF at the fovea, as well as the near and far retinal periphery: y=6.83-6.08e-x/12.2. The overall pattern of retinal defocus was analyzed for both far (0.16D) and near (2.5D) viewing conditions, and it was found to change from predominantly myopic-defocus to predominantly hyperopic-defocus as the target shifted from far to near. In addition, a two-dimensonal dioptric schematic representation of the blur-free region was depicted for a near viewing condition (2.5 D), under which the total DOF encompassed the dioptric region from 0 to 5 D once retinal eccentricity reached 15º and beyond. Lastly, the dynamic nature of blur perception was demonstrated following blur adaptation and for an extended target.
This conceptual model has implications with respect to accommodative control, depth perception, and refractive error development. (1) All earlier bioengineering models of accommodation incorporated a static DOF element limited to the fovea. The new model results showed the DOF and retinal defocus patterns to be dynamic and furthermore to be influenced by the fovea, as well as the near and far peripheral retina. (2) Retinal defocus blur thresholds may provide information related to the depth of objects across the visual field. (3) Differences in retinal defocus patterns under far and near viewing conditions may provide insight into myopia progression.
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