Optical Performance Of Biconvex Toric Intraocular Lens

Cornea astigmatism is a common refractive error; there are20%cartaractpatients with preexisting cornea astigmatism before surgery. How to avoid thesurgically induced astigmatism was a hot topic now. Although many peopleprovided several incision methods to minimize the astigmatism for cateractsurgery, it is still not predictable and stable. Furthermore, cornea relaxingincision has a few problems.Toric IOL is IOL with different optical power and focal length in twoorientations to each other, which used to correct cornea astigmatism. Irregularastigmatism caused by keratoconus, cornea trauma or transplantation evencould be benefit from it.Given that toric IOL has two optical powers in two perpendiculardirections, it could result in images fusion problem of binocular vision.Recently a huge research focused on the relationship between imageperformance and toric IOL decentration and rotation.With progression of study about wavefront aberration in eye with phakicIOL, patient abtained better qulity of vision than before. However, wheatherbetter image performance can be abtained through provement of opticalstructure and optimism of the toric IOL SA, and keep better tolerlance fordecentration and rotation still elusive.Part1Optical performance of biconvex toric intraocular lens based onschematic eyeObjective: To evaluate image performance, depths of focus andlongitudinal chromatic aberration of spherical, aspherical and toric IOL underpolychoromaticlight by schematic eye.Methods: Using Zemax software, we set up Hwey-Lan Liou schematiceye and evaluated image performance, longitudinal chromatic aberration anddepths of focused of TecnisZA9003IOL、SN60AT IOL、Toric IOL by ray tracing method.Results: The image performance was better by asphrecial IOL than thatby sphrecial IOL and toric IOL under polychromatic light. The latter IOLshave the similar result. The lower Abbe number of IOL means lower LCA;SN60AT and toric IOL displayed the same LCA. The LCA was larger for shortwavelength compared with long wavelength. The defocus MTF of bothspherical and toric IOL were decreased and shifted to minus positioncorresponded with pupil size increasing. With the pupil diameter increasing,the defocus MTF of asphrecial IOL keep stable, but depth of focus obviouslydecreased.Conclusion:(1) There were similar image performance of toric IOL andsphrecial IOL.(2) The higher Abbe number was, the smaller LCA of IOL was.(3) For all three kind of IOL, the depth of focus was decreased when the pupildiameter increased, moreover, toric IOL and spherical IOL displayed welllight focus during minus defocus shifting.(4) The aspherical IOL did not showgood light focus under minus defocus shifting with lower depth of focus.Part2Optical performance of biconvex toric intraocular lens withrotation and decentrationObjective: To evaluate the optical performance and wavefrontabrrveation with toric IOL rotation and decentration.Methods: Under550nm wavelength light, we set up differentdeconcentrited SN60AT and toric IOL with the role as follows: deconcentrited0.25mm,0.5mm, and0.75mm at direction from0to90degree with5degreeinterval. Furthermore, we individually rotated toric IOL at3,5,7,10degrees.Then we recorded the image performance and wavefront abrrveation under allconditions. We also evaluated the relationship between rotation and residulrefractive error.Results: SN60AT and toric IOL displayed the similar imageperformance when IOL was centration. The quality of image was decreasedwith the pupil diameter increasing for both IOLs; the decentration of toric IOLin any direction did not influenced the image performance. The RMS was increased when the level of decentration of SN60AT andtoric IOL was increased, which mostly due to the increase of coma abrrationand lightly increasing of trefoil aberration.High space frequency showed worse image performance with increasedrotation degrees of toric IOL; toric IOL rotation caused the increase ofmastigmatism but not high order aberration. That rotation of toric IOLincreased residual astigmatism and spherical error.Conclusion:(1) The optical performance of toric IOL was lightly worsethan that of spherical IOL， which was only related to the amount ofdecentration with no matter of direction.(2) The wavefront aberration causedby decentration of toric IOL included obviouly increased coma and lightlyincreased astigmatism and trafoil aberration.(3) Toricl IOL rotation leaded toincrease of astigmatism and spherical refractive error but not high aberration.Part3Biconvex toric intraocular lens optimizing and opticalperformance of with rotation and decentrationObjective: To optimize toric IOL by SA adjustment and to understand therelationship between image performance and IOL rotation or decentration.Methods: Under the monochromatic light of550nm wavelength, wecarried up two step optimism strategy for toric IOL.(1) Adjustment thecurventure of IOL spherical surface to make theC04minimization as the target.(2) Optimism of SA of toric IOL. Optimism of IOL front surface Q-value and2ndand4thhigh order aspherical coefficient.Furthermore, we analyzed the images performance and wavefrontaberration changes when spherical and aspherical IOL was decentrated athorizental direction with0.25mm、0.5mm、0.75mm and rotated by differentdegrees.Additionally, we tested the spherical and aspherical IOL decentration androtation under different pupil diameters, subsequently, analyzed by MontaCalo mode.Results: The aspherical toric IOL displayed the better image performancewhen it is centered, especially when pupil becoming bigger. MTF of spherical and aspherical toric IOL were similar with3mm pupil and0.25mmdecentration. Toric IOL of-0.26μm SA with more than0.5mm decentrationwas worse compared with0or-0.1μm SA IOL under3mm pupil diameter.When decentrated0.75mm, toric IOL with0SA displayed better than others interms of low and middle space frequency. At4mm pupil diameter, toric IOLwith-0.1μm SA presented best image performance compared with others. At5mm pupil diameter, in terms of low and middle space frequency, toric IOLwith-0.26μm SA displyed better image performance compared with othertoric IOL when decentrated0.25mm. The IOL with-0.26μm SA and sphericalIOL have the similar MTF, but toric IOL with0or-0.1μm SA displayed thebetter image performance compared with spherical IOL.Conclusion:(1) Aspherical toric IOL displayed enhanced imageperformance, especially,-0.26μm SA toric IOL.(2) Aspherical toric IOL stillkeep better image performance when decentrated or rotated compared withspherical IOL.(3) Through adjustment and optimism of SA, imageperformance could be enhanced.Part4Optical performance of biconvex toric intraocular lens withindividual model eyeObjectives: Collection patients eye parameters with different toric IOLimplanted, to evaluate the image performance by using Zemax opticalsoftware.Methods: First, we examed patients with Pentacam and IOLmasterbefore surgery. Then set up astigmatism model of front surface of cornea andback surface of cornea by Matlab4.5software. Constructed customisedindividual model eye by Zemax software.We calculated cornea SA under light of550nm wavelength and contrastsensitivity of individual model eye under300Td light with3mm pupildiameter and0.3-1Td light with5mm pupil diameter individually.Results: The flat axis Q value of cornea front surface was-0.12±0.22,the steep axis Q value was-0.12±0.23. The Q value of cornea back surfacewas-0.43±0.37; the average SA of cornea was0.23μm±0.18μm （-0.15μm~0.42μm）.Under photopia light or mesopia light, aspherical toric IOL RMS wasbetter than spherical IOL; toric IOL with whole corrected SA displayed bettercontrast sensitivity compared with others, except for-0.26μm SA toric IOLwhich only displayed no significant RMS in low space frequency.Conclusion:(1) We could set up precise cornea astigmatism modelaccording to cornea high data through special formulas.(2) Aspherical toricIOL could compensate for cornea SA and to enhance the contrast sensitivity inindividual model eye in terms of mostly space frequency.Conclusion:1Torci IOL and spherical IOL displayed similar image performance anddefocus characters.2Toric IOL and spherical IOL have the simliar identity aboutdecentration tolerance. The coma aberration was the major wavefrontaberration caused by decentration. Rotation of Toric IOL only causedastigmatism but not high order aberration.3The optimism of SA for toric IOL enhanced the image performance andkept good tolerance for decentration and rotation.4According to cornea high data through special fomulas, we can set upprecise cornea astigmatism model.