Multifocal IOL
Multifocal IOLs consist of multiple zones of lens power allowing for both near and far vision by having more than one focal point.
Types:
Refractive
Diffractive
Combination of refractive and diffractive
Refractive IOLs:
● Different zones of equal refractive power have a common focus. But the light waves in this common focus are out of phase.
● This results in partially destructive interference which negatively affects light intensity in the focus and leads to reduction in brightness and visual acuity.
● Disadvantage: Loss in contrast sensitivity upto 50% when compared to a monofocal lens.
● Due to the concentrical arrangement of the different refractive zones, the visual acuity
in either of the foci in the refractive lens depends on pupillary diameter. Eg. Amo Array
Diffractive IOLs:
● They are based on the Huygens-Fresnel principle.
● They have patterns of rings that produce two primary focal points independent of
pupillary aperture.
● Anterior aspheric surface- Basic refractive power
● Posterior surface with multiple grooves- diffractive power
● Advantage: The incident light is distributed 41% to distant focus and 41% to near focus.
This asymmetrical light distribution improves contrast sensitivity.
● The optics work independent of pupillary size.
Eg. Tecniz ZM 900 MFIOL
Refractive-Diffractive IOL’s :
● They are designed and manufactured with a soft transition (phase zones) between the main zones.
● Advantage: Significant reduction in disturbing light phenomena such as scattered light or haloes.
Eg. Alcon Acrysof ReSTOR
Pre-op considerations :
● Strong desire to be spectacle independent
● Patients often complain of the difficulty in multitasking post IOL surgery with monofocal
lens implant .This category of patients are the ones to target for multifocals.
● Rule out preexisting ocular diseases like ARMD,GLAUCOMA etc. more so in these cases as these are visually and surgically demanding cases where the real benefits of multifocality may not be produced or appreciated by the patients. Secondly a partial contrast loss due to the multifocal lenses may add on the visual handicap of the patient.
Patients to be excluded:
● Patients with >1D corneal astigmatism
● Pre existing ocular pathology
● Those with monofocal lens in one eye
● History of previous refractive surgery
● Demanding patients
Intra op exclusion criteria:
● Significant vitreous loss
● Pupil trauma
● Zonular damage
● Capsulorhexis tear
● PCR
Limitations:
● Reduced contrast sensitivity
● Glare and haloes
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