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Aspheric intraocular lens in cataract surgery

Nanavaty, M. A. (2019). Aspheric intraocular lens in cataract surgery. (Unpublished Doctoral thesis, City, University of London)

Abstract

This thesis, by prior publication, encompasses an overview and critical analysis of 6 publications on aspheric intraocular lenses (IOLs) carried out at St. Thomas’ Hospital, Guy’s & St. Thomas’ NHS Foundation Trust, London between 2006 2012. The focus is on two areas: the visual and optical performance of aspheric IOLs with different values of asphericity, and their effect on posterior capsule opacification (PCO). Chapter 1 describes the history of IOLs and the evolution of aspheric IOLs. It also presents relevant optical concepts.
The three publications presented in Chapter 2 compare aspheric IOLs with spherical IOLs. The results come from two prospective, randomised, fellow-eye comparison studies: one comparing a spherical Alcon AcrySof SN60AT versus the aspheric Alcon AcrySof SN60WF (with negative asphericity), which partially corrects corneal spherical aberrations, and the other comparing the Zeiss AcriSmart 36A (with negative asphericity), which partially corrects corneal spherical aberrations, and the Bausch & Lomb Akreos MI60 (with neutral asphericity), which has zero spherical aberration. The third publication reports changes in vertical coma after implantation of all
the above lenses and additionally includes data on two spherical IOLs from a previous study by our group (the three piece Alcon MA60AC IOL and the plate haptic HumanOptic MC611MI IOL). For this study, the data were divided according to their asphericity and not design. To avoid confounding from aberrometric differences due to astigmatism and surgical techniques, standard incision sizes of 2.75 mm and 2.4 mm were used in the two felloweye, randomised studies and a single surgeon performed all the surgeries using same incision size for each study. Results demonstrated that the aspheric IOLs significantly reduced spherical aberration, improved mesopic contrast sensitivity and reduced depth-of-focus. Asphericity differences up to 20 μm were not associated with depth-of-focus and the degree of asphericity was not associated with best-corrected distance visual acuity. The vertical coma varied within IOL groups of the same asphericity but there was no statistically significant difference between the two spherical IOLs (AcrySof SN60AT and AcrySof MA60AC). Further critical analysis of our data already published showed no statistically significant difference in mean vertical coma between the AcrySof MA60AC (-0.060 ± 0.211μm) with that of Akreos MI60 (- 0.042 ± 0.148μm) (p=0.70) and AcriSmart 36A (-0.034 ± 0.141μm) (p=0.58) even though the AcrySof MA60AC, Akreos MI60 and AcriSmart 36A IOLs had different asphericity. This may be due to the difference in the IOL designs, decentration and difference in the sample sizes between groups.
Chapter 3 discusses the findings of three publications related to posterior capsule opacification (PCO). The first publication is an in vitro study assessing posterior optic square edges of various commercially available spherical and aspherical IOLs. Results demonstrated hydrophilic IOLs had less sharp square edges compared to hydrophobic IOLs. Although these in vitro results are potentially significant, there are currently no in vivo studies on the lenses used to compare our results with. The other two publications are based on the PCO outcomes from the prospective, randomised, fellow-eye studies described above. There was no difference in the PCO rates between hydrophobic spherical AcrySof SN60AT and aspheric AcrySof SN60WF IOLs of the same design at 2 years. In contrast, we found a significant increase in the PCO with both the hydrophilic acrylic AcriSmart 36A and Akreos MI60 IOLs (one with negative asphericity and one with neutral asphericity). Variation in asphericity did not appear to be an important factor contributing to the PCO but it was apparent that the edge design and material of the IOL were important with regards to the PCO formation.
Finally, since these publications, some of manufacturers have changed their IOL models and today a majority of the IOLs have are aspheric and have a sharp edge profile. The overall, benefit of using aspheric IOLs seems to be limited as it is dependent on the natural pupil size.

Publication Type: Thesis (Doctoral)
Subjects: R Medicine > RE Ophthalmology
Departments: Doctoral Theses
Doctoral Theses > School of Health Sciences Doctoral Theses
School of Health Sciences > Optometry & Visual Science
URI: https://openaccess.city.ac.uk/id/eprint/23663
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