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Y. Chang, H.-M. Wu, Y.-F. Lin; The Axial Misalignment Between Ocular Lens and Cornea Observed by MRI at Different Accommodative States. Invest. Ophthalmol. Vis. Sci. 2007;48(13):989.
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© ARVO (1962-2015); The Authors (2016-present)
To understand the behavior of lens tilt and decentration relative to the corneal axis during accommodation in 3D is helpful for correcting the human refractive error.
MR imaging system equiped with ocular coil was used to auquire ocular images in 6 healthy subjects with average age of 23.2 +/- 1.1 years. MRI sequence was SPGR TR/TE/Flip angle = 18.6 ms/ 5.4 ms/ 25 deg, slab thickness = 3.12 cm, individual slice thickness = 0.6 mm, field of view (FOV) = 4 cm x 4 cm, pixel matrix = 128 x 128 zip to 512 x 512, number of average (NEX) = 8, bandwidth = 9.62 KHz. The fixation target was set at 60 (Far), 40 (Mid) and 20 (Near) cm away from the eye to form different accomdative states for the subject. One month later, retest was carried out in 5 of the 6 subjects for longitudinal study. Lens tilts of anterior and posterior surfaces and decentration with respect to corneal axis were measured.
The tilting angles of lens anterior surface to corneal axis, posterior surface to corneal axis and decentration (in mm) for Far/Mid/Near of the test were 3.7±2.5 / 2.1±0.9 / 1.4±0.5 (deg), 3.3±1.4 / 2.3±1.2 / 2.0±0.9 (deg)and 0.14±0.05 / -0.11±0.23 / -0.11±0.11 (mm) (H), -0.10±0.34 /-0.14±0.48 / -0.11±0.11(mm) (V) respectively. For retest, they were 2.1±2.4 / 1.7±1.7 / 1.8±1.1 (deg), 1.9±1.8 / 2.3±1.6 / 2.2±2.6 (deg) and -0.02±0.28 / -0.10±0.20 / -0.09±0.07(mm) (H), -0.45±0.28 / -0.18±0.73 / -0.21±0.46 (mm) (V) accordingly. By statistical test, no significant difference was shown between test and retest in lens tilt and decentration.
It seems that there is no rule for the lens orientation with respective to the corneal axis when accommodation is aplied according to this study with a limited sample size. However, one may notice that the mean tilt value at Far could be larger than the other accommodative states, although it may not be true for the posterior lens in retest, it is close.
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