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L. N. Davies, C. J. Evans, A. L. Sheppard, K. D. Singh; Development of an in vivo 3-D Magnetic Resonance Imaging Technique for the Human Crystalline Lens. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5788.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a Magnetic Resonance Imaging (MRI) protocol to enable 3-D imaging of the whole crystalline lens and surrounding architecture.
Three subjects took part in the study (aged 19 to 30 years). T2-weighted MRIs, optimised to show fluid-filled chambers of the eye, were acquired with a General Electric (GE) 3T HDx system, using an 8-channel head RF coil. Sagittal, axial and coronal localiser scans were acquired, during which the subjects were instructed to fixate on a distant (6m), high contrast (90%), Maltese cross target. Data were acquired using the vendor's Fast Spin Echo (FSE) sequence using the following parameters: TE/TR=500/8580ms; echo-train=24; bandwidth=±15.63kHz; acquisition matrix=256x256; field-of-view=205mm; 3 averages. Total acquisition time was 5:18min. Twenty-four oblique-axial slices of 0.8mm thickness were aligned parallel with the optic nerve. The inherent motion sensitivity of the acquisition can result in image artefacts due to subject eye blinks during the scan; thus, each subject was instructed to fixate and supplied with a button box connected to a PC, allowing the scan to be paused when the subject needed to blink. Three accommodative stimuli (0.17, 4 and 8D) were presented randomly to the subjects in the MRI to examine lenticular changes with accommodation. MRIs were analysed using a modified version of the freeware software package mri3dX. The software utilises automatic segmentation and meshing algorithms to generate a 3-D surface model, which can provide a variety of data including: surface curvature; lens thickness; equatorial diameter; surface area; and volume.
The spatial resolution of the 3-D MRIs enabled crystalline lens changes to be measured over the 8D stimulus range. An increase in lens thickness (0.046mm/D) was observed during accommodation, which accompanied a decrease in equatorial diameter (0.072mm/D). Moreover, the technique showed that the radius of both the anterior (0.762mm/D) and posterior (0.152mm/D) lens surface decreased with accommodation.
The MRI acquisition and analysis protocol provides a novel way of examining change in both lenticular and extra-lenticular structures during accommodation in the human eye. Further use of this technique in a larger cohort will enable quantification of lens changes in both the phakic and pseudophakic eye.
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