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Y. Chang, H. Wu; Lens Displacement on Accommodation Observed by MRI . Invest. Ophthalmol. Vis. Sci. 2003;44(13):233.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To verify whether ocular lens has any displacement or not on accommodation, MRI technique is employed to provide an objective observation in this study. Methods: Six young students in this Institute were served as subjects. A total of six eyes had been examined by using 1.5T (GE) MRI machine at VGH. Parameters for pulse sequence were given: 3' surface coil, 3D FSPGR, TR/TE/Flip angle = 18.6 ms/5.4 ms/25 deg, slab thickness 3.12 cm, individual slice thickness 0.6 cm, FOV 4.0 cm x 4.0 cm, matrix 128 x 128 zip to 512 x 512, number of average = 8, bandwidth = 9.62 KHz. The targets for fixation, one with a thin cross mark was set about 20 cm in front of the eye as near point and the other was 60 cm as far point, can be observed through a reflective mirror by the subject who is in supine position. A third target was put on the fixation line in between of the two targets for fixation at the distances of 60, 40 and 20 cm from the eye. The lens images in different slices were extracted by using threshold selection method to reconstruct a 3-D lens image. A total of three 3-D lens images were obtained with different accommodative amplitudes. Results: All subjects have shown that the anterior lens vertex moves toward the corneal site in an average of 0.27+/-0.16 mm, posterior lens vertex moves toward the retinal site with 0.10+/-0.03 mm in 4 subjects, one has no change and one moves to corneal site of 0.03 mm. Lens tilting and shifting are also observed on accommodation. Three Lenses tilt to the nasal-inferior site with 2.71+/-0.87 deg and 0.28+/-0.11 mm shift, two tilt to the temporal-inferior site with 3.43+/-1.22 deg and 0.32+/-0.01 mm shift, one tilts to nasal-superior site with 6.93 deg and shifts 0.19 mm. Conclusions: Lens displacement on accommodation can be observed by an objective method of MRI technique. The findings show that lens moves toward the corneal site on accommodation, which are consistent in all subjects. Phenomena of lens tilting and shifting are also observed in this study, however the tilted directions are not consistent.
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