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K. H. Edwards, H. Proskin; Mathematical Analysis of Defocus Curves in the Assessment of Accommodation. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4552.
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The effect of positive and negative lens induced blur on visual acuity has been used to investigate the potential improvements in depth of field and/or genuine accommodation with multifocal and potentially accommodating intraocular lenses (IOLs).Accommodation is only demonstrated when there is asymmetry in the speed of visual reduction between positive and negative lens defocus, negative defocus causing less visual loss in the presence of accommodation.
The authors investigated a curve fitting algorithm that utilizes separate best-fit quadratic curves for positive and negative defocus values, subject only to the constraint that the curves intersect at the zero defocus point. Once the estimated curves have been established, the respective defocus powers necessary to maintain a given level of acuity can be extrapolated and the difference between them used to calculate the effective accommodation.
By using data from defocus assessments of a potentially accommodating IOL, this methodology provided good assessments of real "accommodation" and could differentiate this from cases where good near acuity was evident despite a lack of accommodation, suggesting an enhancement to depth of field.
The mathematical analysis provided objective and reliable assessments of genuine accommodative effect.
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