2 types!
1) Refractive Type:
-They have annular zones of different refractive powers to provide focus for near and far objects.
-Dependent on the size of the pupil to utilize the required zone of lens.
-Limitations: a high incidence of dysphotopsic symptoms, high intolerance to pupil decentration and large angle kappa, and a significant loss of contrast sensitivity.
2) Diffractive Type:
-These IOLs are engineered with microscopic steps on its surface with a specific phase delay, usually half a wavelength, following the Huygens-Fresnel principle.
Light falling on such a surface is divided into two foci (41% each) for distance and near, while around 18% light is lost to higher order aberrations (HOA).
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