Authors: Chai Qiannan, Zhang Bin, Geng Yuxin, Du Yinghua, Liu Danyan, Ma Feiyan, Wei Yuhua
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Background
Cornea astigmatism can be effectively corrected by implanting Toric intraocular lens (IOL) during cataract surgery and therefore improve visual acuity of patients.However, the decentration and rotation position errors were inevitable sometime.What’s the difference of effect of position errors on quality of image between spherical IOL and Toric IOL needs further research.
Objective
This study was to evaluate the optical performance and wavefront with rotation and decentration of Toric IOL.
Methods
Different decentration for SN60AT IOL(spherical IOL) and Toric IOL in Hwey-Lan Lion model eyes was set with the role as follows: decentration 0.25 mm to 0.75 mm in a 5°-interval from 0° to 90°.Furthermore, Toric IOL was rotated at 5° and 10°, respectively.Then the image performances of SN60AT IOL and Toric IOL at different decentration distances and rotated degrees were evaluated with modulation transfer function (MTF) and value of wavefront aberration under all conditions.
Results
At the centration, the MTF curves of spherical IOL and Toric IOL were similar under 3, 4 and 5 mm pupil diameter at each spatial frequency.Under the condition of 4 mm pupil diameter, when the decentration was 0.25 mm, the MTF values of SN60AT IOL at 6 c/d and 12 c/d were 0.581 087 and 0.411 960, respectively.T3 IOL were 0.454 259 and 0.382 313, T4 IOL were 0.426 020 and 0.360 490, T5 IOL were 0.425 606 and 0.359 877.When the decentration was 0.50 mm, the MTF values of SN60AT at 6 c/d and 12 c/d were 0.573 073 and 0.412 787, respectively.T3 IOL were 0.450 943 and 0.379 481, T4 IOL were 0.423 153 and 0.356 664, T5 IOL were 0.422 881 and 0.356 230.When the decentration was 0.75 mm, the MTF values of SN60AT at 6 c/d and 12 c/d were 0.560 038 and 0.413 624, respectively.T3 IOL were 0.445 597 and 0.374 322, T4 IOL were 0.418 522 and 0.350 087, T5 IOL were 0.418 468 and 0.349 976.When the IOL decentralized along 0°, 5°, 10°, 90°meridian line, the MTF values were almostly same.The root mean square (RMS) of spherical IOL and Toric IOL was increased when the IOL decentralized from 0 mm to 0.75 mm, with the most increasing level in coma aberration and slight increase in trefoil aberration.When the T4 IOL decentralized from centre to 0.75 mm, the coma increased from 0 to C(3, -1) -0.049 79 μm, C(3, 1) -0.037 59 μm and the trefoil aberration increased from 0 to C(3, 3) 0.005 72 μm, C(3, -3) 0.004 64 μm.With the increase of rotation degrees (from 5°to 10°) of Toric IOL, the MTF was worse at high spatial frequency.Toric IOL rotation caused the increase of astigmatism and residual astigmatism and spherical error, but not high order aberration.
Conclusions
The tolerance of Toric IOL to decentration is very close to the spherical IOL, and optical performance is only associated with the amount of decentration but not direction.The aberration caused by Toric IOL decentration is mainly coma.The rotation of Toric IOL causes astigmatism error but not high order aberrations.