Glistenings in Intraocular lenses and their effect on forward light scatter; an in vitro study

Introduction. Glistenings are fluid-filled inclusions in the polymer matrix of an intraocular lens (IOL). Acting as refractile particles they may contribute to a reported high level of forward light scatter. However, several studies have reported that there is no significant correlation with a number of measures of visual function. The purpose of the work reported in this thesis was to test if there was an association between in vitro forward light scatter and grade of glistenings. The in vitro approach allows measurement of forward light scatter without the confounding effects of other structures in the eye and subjective responses. Methods. Intraocular lenses were placed at the centre of rotation of a detector stage. The detector measured the forward scattered light in star space at 37 angles covering ±18 degrees. Measurements were made for each of the test lenses at 3mm, 4mm and 5mm pupil sizes. Forward light scatter was quantified by calculating the straylight (volume under the scatter function) for the large angle domain (> 1 deg.). Images of the intraocular lenses were captured with a digital Nikon FS-2 photo slit-lamp. Having developed a Glistenings Detection Programme (GDP) in collaboration with external computer scientists, images were analysed. Results of glistening detection, which included their number, size, density and distribution, were correlated with in vitro forward light scatter measurements. Results. A statistically significant correlation was found between forward light scatter and the number, size and density of glistenings. Comparing our scatter results with the CIE standards, suggests that only high glistenings severity could have an impact on visual function. In addition, results were inversely proportional to pupil size due to the non-uniform distribution of glistenings. The shape of glistenings was shown to be predominantly ellipsoidal rather than spherical. Size and number of glistenings varies in the hydrophobic acrylic materials. Despite the production of new glistenings-free materials, development of glistenings may still exist with cases of high severity giving straylight parameter values greater than those for a cortical cataract subject. A statistically significant difference in MTF and Resolution limit was found in IOLs, pre and post thermal treatment. Finally, a correlation between IOL dioptric power and severity of glistenings was found. Conclusion. Subjective methods for grading intraocular lens glistenings poorly describe the significance of increased light scattering. Image processing software can provide objective data on glistenings density, size and morphology, factors which are important in light scatter modelling. The impact of glistenings on visual function needs further clinical investigation.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

City University London

Year dc:date.issued

2015

Author dc:creator

• Filippaki, Evangelia

• RE Ophthalmology