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Ji C He, Jianhua Wang, Mian Wei, Jing Mao; Forward movement of the crystalline lens plays an important role in accommodation. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3779.
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© ARVO (1962-2015); The Authors (2016-present)
Helmholtz’s theory predicts an equal or less shortening of the anterior chamber depth (ACD) than the thickening of the lens thickness (LT) during accommodation. But, the relationship between the ACD shortening and the LT thickening has not been well explored yet. The purpose of this study was to measure optical and structural changes in the accommodated eyes.
A custom developed Hartmann-Shack wavefront sensor, integrated with two custom developed spectral domain optical coherent tomography (SD-OCT) systems, was used to measure accommodative responses (AR) for 18 young adults (aged 22 to 27 yrs old, and spherical equivalent Rx ranged -1.50 to +1.00D). The wavefront sensor measured Zernike aberrations up to 7th order for the left eye when accommodative stimulation (AS) was presented for the same eye at 0.0, 2.0, 4.0 and 6.0D with a Badal system. One 840nm SD-OCT system, co-axially aligned with the wavefront sensor, was used to image the cornea and the lens, and the other 1310nm SD-OCT system to temporally image the ciliary muscle contraction.
For all subjects, mean AR increased with AS demand and reached to 5.45±0.27D at 6.0D AS level. Mean Zernike spherical aberration was decreased from +0.04±0.03 micron at 0.0D to -0.03±0.06 micron at 6.0D. The ciliary thickness close to the scleral spur was increased with accommodation. All subjects at 4D and fifteen out of the eighteen subjects at 6D showed a greater amount of ACD shortening than LT thickening. The mean changes in ACD and LT from 0.0D to 6.0D AS were -0.44±0.14mm and 0.22±0.13mm respectively. The LT changed differently from subject to subject, and it increased to more than 0.30mm for some subjects while no change was observed for some others. The LT increase was significantly correlated to the ACD decrease with a slope of 0.70 (r=0.61, p<0.01). Mean radii of the anterior and posterior lens surfaces were reduced from 11.83±1.34mm and 5.39±0.45mm to 7.32±0.62mm and 4.58±0.42mm respectively.
In addition to the changes in the lens curvature and lens thickness, forward movement of the crystalline lens during accommodation plays an important role in increasing refractive power of the accommodated eye. Both lens shape deformation, as suggested by Helmhotz’s theory, and lens forward movement, as suggested by Kepler, are involved in accommodative process.
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