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Modulation Transfer Function (MTF) and Ocular Light Scatter Measured in the Normal Pseudophakic Eye with the Optical Quality Analysis System II (OQAS). Kavita Gala David Spalton Mayank Nanavaty St Thomas’ Hospital , London. No financial interest. Images point spread function

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Kavita Gala David Spalton Mayank Nanavaty St Thomas’ Hospital , London

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Kavita gala david spalton mayank nanavaty st thomas hospital london l.jpg

Modulation Transfer Function (MTF) and Ocular Light Scatter Measured in the Normal Pseudophakic Eye with the Optical Quality Analysis System II (OQAS)

Kavita Gala

David Spalton

Mayank Nanavaty

St Thomas’ Hospital , London

No financial interest


Oqas optical quality assessment system visionmetrics spain l.jpg

Images point spread function

Derives MTF, Strehl ratio, light scatter (OSI – objective scatter index

OSI is an objective parameter of intraocular scattered light calculated by evaluating the amount of light on the outside of the double-pass image in relation to the amount of light on the centre. The higher the OSI value, the higher the level of intraocular scattering.

MTF is the ratio between contrast in the retinal image and contrast of the original object.

Strehl ratio is a measurement of an optical system and is the ratio of the MTF to that of a diffraction limited system. Thus, Strehl ratio will be a figure between 0 and 1, the higher its value, the better optical quality

OQAS(Optical Quality Assessment System – Visionmetrics, Spain)


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Aim

  • To assess the effect of PCO on the OSI and Strehl ratio

  • To compare the OSI and Strehl ratio with aspheric lenses ( Acrismart, Bausch & Lomb MI60, Acrysof IQ) and spheric lenses ( Alcon SA60 and Acrysof Natural )

  • To compare the OSI and Strehl ratio with hydrophilic lenses ( Acrismart and Bausch & Lomb MI60 ) and hydrophobic lenses ( Acrysof IQ, Alcon SA60 and Acrysof Natural )


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St Thomas’ Hospital OQAS

  • Customised software to measure MTF and OSI simultaneously at 4mm pupil

  • Correlation with changes in central 4mm of posterior capsule

  • On going research into quantifying effect of PCO on quality of vision


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Methods

  • All surgeries performed by the same surgeon by a standardized procedure

  • 91 eyes of 57 patients included:

    Acrismart 25

    Bausch & Lomb MI6013

    Acrysof IQ24

    Alcon SA605

    Acrysof Natural24

  • Strehl ratio and OSI values extracted from OQAS


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Methods

PCO

  • A sub group of 13 eyes of 11 patients with retroillumination images with PCO

  • Evaluation of PCO area and severity with POCOman software in central 4 mm of posterior capsule

  • Correlated with OSI and Strehl ratio pre and post Yag


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No Yag

M L OSI 1.3

No Yag

Examples

of PCO

and

OSI values

P H OSI 0.7

RP OSI 1.9

E B OSI 3.3


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E K OSI 4.2

T P OSI 6.5

C C OSI 13.9

E K OSI 9.4


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P=ns

Comparison of Strehl ratio and OSI in patients with clear capsules to patients with PCO pre and post yag

Following Yag capsulotomy there is no difference in values

to clear capsules

P=ns


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There was no significant difference in Strehl ratio between aspheric and spheric IOLs or between hydrophilic or hydrophobic IOLs

In clear capsules

In clear capsules

24

25

13

5

24

The OSI was significantly higher in hydrophilic compared to hydrophobic IOLs

OSI similar between aspheric and spheric lenses

Hydrophilic

Hydrophobic

60

natural

M160


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Conclusion

OSI with PCO

  • Increases with severity

  • Not affected by subtle membranes

  • Individual correlation to PCO rather variable

  • Early days, more cases needed

    IOLs with clear capsules

  • Strehl ratio - no difference between aspheric vs. spheric / hydrophilic vs. hydrophobic IOLs

  • OSI – no difference between aspheric vs. spheric IOLs

  • OSI increased with hydrophilic IOLs compared to hydrophobic IOLs


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