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Background
The optic quality of Toric intraocular lens (IOL)-implanted eye is affected by the residual astigmatism and individual difference of corneal spherical aberration and different magnification from steep and flat axis refraction.Whether correcting Toric IOL spherical aberration can effectively improve the image quality of individual patient is a question to be studied.
Objective
This study attempted to collect eye parameters of cataract patients to reconstruct the customized vision model by using Zemax optical software, and to evaluate the image performance with different Toric IOL spherical aberration.
Methods
A prospective study was performed.Forty-five eyes of 45 cataract patients were included in Second Hospital of Hebei Medical University from August 2012 to October 2013.Several relevant parameters were measured by Pentacam, including anterior and posterior surface height of cornea, corneal thickness, curvature radius of flat and steep meridians of anterior surface astigmatism, refractive diopter and curvature radius of posterior surface.The astigmatism of anterior and posterior corneal surface was described by Matlab 4.5 software.Corneal astigmatism model were set as aspheric state, and the effective position of Toric IOL was calculated using HolladayⅠformula.Customized individual model eyes were constructed by Zemax software.The contrast sensitivity function (CSF) of different spherical Toric IOLs at different spatial frequencies were calculated and compared between 300 Td light environment with 3 mm pupil diameter (photopia light) and 0.3-1.0 Td light environment with 5 mm pupil diameter (mesopia light). This study was approved by Second Hospital of Hebei Medical University ethics committee, all the patients signed the informed consent.
Results
The mean astigmatism power was (1.51±0.36)D and (1.49±0.37)D, and the mean astigmatism meridian was (101.5±59.8)° and (101.9±58.5)° in the model eyes and cataract eyes, respectively, without significant differences between them (t=0.886, 0.652; both at P>0.05). Bland-Altman test showed a good agreement in astigmatism power and astigmatism meridian between model eyes and cataract eyes.The LogCSF values at 1.5, 3.0, 6.0, 12.0 and 18.0 c/d spatial frequencies were significantly higher in the aspherical Toric IOL model eyes than those in the spherical Toric IOL model eyes, and the LogCSF values at various spatial frequencies were significantly higher in the Toric IOLs with spherical aberrations of -0.13 μm and -0.26 μm than those in the zero spherical aberrations in both photopia light and mesopia light (all at P<0.05).
Conclusions
A precise corneal astigmatism model based on cornea high data of cataract eyes was successfully constructed through special formulas with Zemax software.Aspherical Toric IOL can compensate for spherical aberration of cornea and enhance the optic quality in individual model eye.