Abstract
Purpose :
Typically the optical properties of the corneas in keratoconic eyes are significantly affected by irregular astigmatism, even if the progression has stabilized. Up until now, when cataract formation occurs in these eyes the most we can do with Intraocular lenses (IOL) is to take care of the correction of sphere and cylinder which are lower order aberrations. These eyes however, show clinically relevant amount of higher order aberrations (HOA), specially coma and trefoil, therefore only part of the irregular astigmatism is corrected. A possible approach to the problem is the use of a small-aperture-IOL in these eyes.
Methods :
Corneas of keratoconus eyes where measured with a rotating Scheimpflug-camera. The corneal tomography with elevation data of anterior and posterior surface is transferred into an optical design software to modify the Liou-Brennan-eye model with patient specific corneal data. Further adjustments to the standard eye model were done concerning axial length and anterior chamber depth.
Raytracing in these patient models were performed for phakic eyes and pseudophakic eyes with a toric intraocular lens and a spherical lens with a small aperture of 1.3 mm, as it is available on the market (Acufocus IC-8). As far as clinical data are available outcomes of performed cataract surgery are compared with these retrospective simulations.
Results :
After optimization of sphere and cylinder for best focal spot, the two types of lenses can be compared by through focus measurements, wavefront errors and point spread function. The small aperture simulations show better spot pattern in the through focus simulations as well as better point spread function compared to toric iol for cornea with high irregularities. Since the number of cases is limited and keratoconic eyes show large interpatient variabilities no statistic values for the increase in strehl ratio or reduction in astigmatic power can be given and only case examples can be done. Anyhow these findings are confirmed by retrospective analysis of the surgical outcomes concerning shape of the point spread function.
Conclusions :
For patients with irregular corneas phacoemulsification and implantation of small-aperture-IOLs provide an alternative option for the correction of astigmatism compared to toric intraocular lenses.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.