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M. Dubbelman, E. A. Hermans, G. L. van der Heijde, R. M. Heethaar; The Change of the Equivalent Refractive Index of the Crystalline Lens as a Function of Accommodation Response Measured With Scheimpflug Imaging and Aberrometry. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3775.
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© ARVO (1962-2015); The Authors (2016-present)
To experimentally verify the suggestion of Gullstrand (1911) hat the equivalent refractive index of the human lens increases with accommodation.
For five subjects, the left eye was used to focus at a different accommodation stimulus, while the right eye was imaged using corrected Scheimpflug photography in order to obtain the shape of the lens and cornea during accommodation. Thereafter, the procedure was repeated, but instead of the Scheimpflug imaging, the accommodative response of the right eye was measured objectively with an aberrometer. Finally, the axial length was measured using the Zeiss IOL-master. Combining the results of all these measurements allowed correction of the digital Scheimpflug images for corneal and lenticular refraction and simultaneously calculation of the equivalent refractive index of the lens for all different accommodative stimuli. This equivalent refractive index is based on the assumption that the lens consists of a homogeneous medium with a single refractive index.
Mean equivalent refractive index (±s.d) was 1.4345±0.008). For all five subjects, there was no significant change in the equivalent refractive index of the lens as a function of accommodation. Furthermore, the accommodative response appeared to be lower than the accommodative stimulus (i.e. accommodative lag).
Gullstrand suggested that the change of power of the lens needed for accommodation does not result of changes in lens thickness and surface curvature alone, but also from changes in the refractive index distribution within the lens. As a result, there would be an increase in the equivalent refractive index with accommodation. He called this process the intracapsular mechanism of accommodation. However, our results make it clear that the equivalent refractive index of the lens does not change with accommodation when the accommodative lag is taken into account.
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