1. Reproducibility of Optical Measurements in Pseudophakic eyes Using Double-Pass Measurement System St Thomas Hospital, London Anish Dhital, David Spalton, Kavita Gala ASCRS 2010 No Relevant Financial Disclosure

2. Purpose To measure the reproducibility of optical measurements in pseudophakic patients using a double pass measurement system. Light scatter Increasing interest in measurements of light scatter and impact on visual function Methods of measuring scatter Double-pass Psychophysical Hartmann-Shack

3. Variables that affect light scatter Tear film Cornea Anterior Chamber Intra-ocular lens Vitreous clarity Measurement error inherent in the system may also affect the repeatability of measurements Montes -Mico et al IOVS 46:12:4468-44742005 Nanavaty et al Ophthalmogica in press

4. Optical Quality Analysis System II (OQAS) Uses double-pass measurement system Images point spread function Derives MTF, Strehl ratio, light scatter (objective scatter index - OSI) (Visionmetrics, Spain) MTF - the ratio between contrast in the retinal image and contrast of the original object. OSI - objective parameter 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. Higher OSI value relates to more intraocular scattering. Strehl ratio - measurement of an optical system (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

5. Methods Prospective reproducibility study Population Normal pseudophakic eyes, At least three months post-cataract surgery Measures Refraction OQAS measurements used customised OQAS II machine

6. Methods Refraction - to obtain the cylindrical correction to optimise measurement. OQAS II - Pupils were dilated and measurements made for a 4mm exit pupil diameter. 3 sets of measurements of OSI and Strehl ratio from a single eye at one visit were taken and the average calculated. This was repeated one to two weeks later. Correlation plots and Bland-Altman analyses were used to assess and compare the 2 sets of measurements.

7. Results 51 eyes from 29 patients were assessed, with a heterogenous group of intraocular lenses: 20 eyes with an Alcon SA60AT 5 eyes with an Akreos MI60, 6 eyes with an Acrismart 36a IOL, 6 eyes with an Alcon SA60WF 6 eyes with the Morcher 89A ‘Bag in the Lens’ 2 eyes with Crystalens HD intra-ocular lens. 6 eyes with unknown IOL type

8. Results R 2 = 0.78 Average of 2 nd reading Average of 1 st reading Correlation of Strehl ratio values

9. Results Correlation of OSI values R 2 = 0.95 Average of 1 st reading Average of 2 nd reading

10. Results Bland-Altman Plot of Strehl ratio Coefficient of Repeatability = 0.033 Strehl ratio Difference Standard Deviation = 0.017

11. Results Bland-Altman Plot of OSI Difference Ocular Scatter Index Coefficient of Repeatability = 1.56 Standard Deviation = 0.79

12. Conclusion Optical measurements using a double-pass system are reproducible despites concerns of changes in the anterior segment between visits.