Study Of Wavefront Aberrations Of Aspherical Intraocular Lens And Effect On Visual Performance

Objective:1 To investigate the decentration of aspheric and conventional spherical intraocular lens (IOL) effect on wavefront aberration in vitro.2 To study the apparent accommodation of spherical and aspheric IOL based on Liou-Brennan eye model.3 To study optical performance of individual pseudophakic eye model which was constructed based on anatomic parameters of individual patient and IOLs with different optical design were implanted.Methods:1 An optical test bench for investigating wavefront aberrations introduced by IOLs was constructed. Hartmann-Shack aberrometer was used to measure the aberrations.4 IOLs (Tecnis Z9000, FY60AD, SN60WF, YA60BBR) were measured when centered, horizontally decentered 0.2mm,0.4mm,0.6mm,0.8mm and 1.0mm respectively for pupil apertures of 3mm and 5mm.2 Liou-Brennan eye model was built by using ZEMAX optical design program. The natural crystal lens was replaced by IOLs (LI61AO, Tecnis Z9000, FY60AD, Cee On911, SA60AT, YA60BBR and P359UV) to mimic pseudophakic optical system. (1) Ray-tracing method was adopted to calculate optical defocus and analyze pseudophakic accommodation induced by IOL forward movements. (2) Through-focus Modulation Transfer Function(MTF) for 550nm wavelength monochromatic light,6cycles/degree/degree spatial frequency to analyze depth of focus (DOF) for different IOLs.3 The anatomic parameters of individual pseudophakic patients were obtained by Pentacam and IOL Master. These parameters were input into ZEMAX to build individual eye model.4 IOLs (SofPort AO, Tecnis Z9000, FY60AD, YA60BBR) were implanted into individual eye models. MTF and CSF were caculated for 3mm to 5mm pupil diameter and 550nm wavelength.Results:1 The total RMS and 3rd order coma RMS of the 4 IOLs were significantly increased with decentraion for 3mm aperture (P<0.01). The spherical aberration (SA) of spherical IOL did not change significantly (P>0.05); while SA of 3 aspheric IOLs increased significantly (P<0.05); we compared SA of different level of decentraion with centered IOL, found statistic significance when the aspheric IOLs'decentration was equal or larger than 0.8mm (P>0.05).2 The total RMS and 3 rd order coma RMS were significantly increased with decentration for 5mm aperture (P<0.01). SA of spherical IOL was slightly increased with decentration (P>0.05); while increases of 3 aspheric IOLs were significant (P<0.05). We compared SA of different level of decentraion with centered IOL, found statistic significance when aspheric IOLs' decentration were equal or larger than 0.8mm (P>0.05).3 Pseudophakic accommodation increased linearly with both spherical and aspheric IOLs' anterior movements, it was slightly larger in spherical IOL.4 Both spherical and aspheric IOLs showed increased DOF with pupil diminution, spherical IOL could tolerate more negative defocus compared with aspheric IOL, this tendency was more predominant for larger pupil diameter.5 The MTF and CSF curves were similar with 3 aspheric IOLs and 1 spherical IOL implanted in the individual eye models for 3mm pupil diameter.6 The MTF and CSF curves of 4 IOLs implanted into the individual eye models were dissimilar with each other, indicated that the individual person with different anatomic structures need certain type of IOL to obtain optimal optical performance.Conclusions:1 Decentration of IOL caused increase of total RMS and 3order coma RMS, while SA of spherical IOL (YA60BBR) was stable, and SA of aspheric IOLs (Tecnis Z9000, FY60AD, SN60WF) were almost stable. The increases of coma and other asymmetric aberrations induced by IOL decentraion were the main reason to cause image quality deterioration.2 Pseudophakic accommodation caused by IOL forward movements was slightly lower in aspheric IOL. The negative SA of aspheric IOL compensated corneal inherited positive SA, caused decrease of orbital SA. MTF of aspherical IOL would be higher than spherical IOL when well focused, while decreased with defocus promptly, with cost of DOF and tolerance of defocus in aspheric pseudophakic eye.3 The individual eye model based on individual patient's anatomic parameters could mimic optical performance of individual eye. The type of IOL was varied to obtain optimal optical performance for optical system of human eye with different anatomic structure.