Clinical investigations into contemporary cataract surgery

Abstract

Cataract extraction and implantation of an intraocular lens (IOL) is the commonest surgical intervention in the developed world and one of the most successful. Such achievement is the result of continuous research over the past decades, including optimization of the material and optical properties of IOLs and of the techniques and equipment used to undertake cataract surgery. IOLs implanted during cataract surgery need to meet basic criteria including biocompatibility, long-term maintenance of clarity and shape after implantation and have excellent optical properties. Glistenings are small, fluid-filled vacuoles that can develop within IOL materials. They alter transparency and have the potential to impair post-operative visual performance. As such, lens manufacturers and researchers alike have sought to identify their causation, evaluate their visual consequences and reduce their occurrence, particularly with the development of new IOL material polymers and manufacturing processes. The optical properties of modern IOLs are highly sophisticated. They are designed not only to optimize the post-operative spherical refractive error but typically incorporate aspheric surfaces to reduce higher order aberrations. Pre-existing corneal astigmatism is common in patients undergoing cataract surgery and failure to correct it can result in sub-optimal visual outcomes. One methodology to address corneal astigmatism is to implant IOLs with a toric refractive component (TIOLs). However, TIOLs are not universally available within the National Health Service (NHS) in the United Kingdom. The reasons for this lack of availability are related to the additional costs, both financial and in time, associated with their usage and complexities around procurement and stock management, given the large number of possible spherical and cylindrical power combinations that exist for TIOLs. Modern small incision cataract surgery is very precise and highly exacting in terms of surgical skill. Over the past decade the introduction of femtosecond laser–assisted cataract surgery (FLACS) has ignited excitement due to its potential to both automate and improve surgical precision. However, current evidence indicates that FLACS is only comparable and not superior to conventional phacoemulsification cataract surgery (CPS) and is associated with additional costs. This has been a significant impeding factor in the utilization of this new technology within the NHS, although evidence from comparative studies with long-term follow-up (12 months or longer) is at present limited. The work in this doctoral thesis explores various aspects of the technologies employed in modern small-incision cataract surgery. The first part (chapters 2,3 and 4) addresses IOL glistening degradations, their effects on visual function and their occurrence in new acrylic polymer, hydrophobic, so-called “glistenings-free” IOLs. The second part (chapters 5 and 6) explores the adoption of premium surgical technologies, such as FLACS and TIOLs for cataract surgery delivery in the National Health Service. As such, this thesis comprises an introductory chapter (chapter 1), a literature review (chapter 2) and then four chapters based on five studies: CHAPTER ONE: Introduction to modern small-incision cataract surgery and the technologies employed in its undertaking. CHAPTER TWO: Introduction to intraocular material degradations (Literature review). This is a comprehensive review of published scientific literature concerning clinical and material degradations of intraocular lenses after implantation in cataract surgery. CHAPTER THREE: Effects of intraocular lens glistenings on visual function: a prospective study and presentation of a new glistenings grading methodology. A new highly reproducible grading methodology was developed with optimum equipment settings specifically developed for the purpose of grading glistenings and with carefully controlled ambient illumination. In the cohort that was studied, glistenings in the same hydrophobic acrylic IOL after cataract surgery were not associated with visual function parameters, including visual acuity, positive and negative contrast sensitivity at 10 cycles per degree, and forward light scatter. CHAPTER FOUR:  Visual and refractive outcomes and glistenings occurrence following implantation of two monofocal, aspheric, hydrophobic acrylic intraocular lenses: Clareon® (Alcon Laboratories Inc.) and Tecnis PCB00® (Johnson & Johnson Inc.). The aim of this study was to compare the Clareon® (Alcon Laboratories, Inc.) IOL to the Tecnis PCB00® (Johnson & Johnson Inc.) in terms of visual performance, refractive outcomes, glistenings occurrence and quality-of-life outcomes. This was the first RCT to investigate the Clareon® and the first to compare it to PCB00®. The study concluded that there were no differences in visual outcomes between the two IOLs. Glistenings were rarely observed in either IOL with no difference in grades. There was no difference in perioperative or postoperative complications. Surgeon optimization of the A-constant for the Clareon IOL is recommended. CHAPTER FIVE: A randomized, prospective study of “off-the-shelf” use of toric intraocular lenses for cataract patients with pre-existing corneal astigmatism in the NHS The aim of this study was to compare visual and refractive outcomes of monofocal IOLs with limbal relaxing incisions (LRI) with “off-the-shelf” use of toric IOLs (TIOLs), with a fixed 2-diopter cylinder (DC) correction, for cataract patients with pre-existing corneal astigmatism in a public-sector setting. This study concluded that TIOLs with a fixed 2.00 DC correction during cataract surgery may improve UDVA, reduce post-operative cylinder and result in a more reliable astigmatic correction compared with monofocal IOLs with LRIs. CHAPTER SIX: A randomized controlled trial comparing femtosecond laser–assisted cataract surgery versus conventional phacoemulsification surgery (FLACS RCT): 12-month results. This was an analysis of 12-month outcomes of a randomized controlled trial comparing conventional phacoemulsification surgery (CPS) with femtosecond laser–assisted cataract surgery (FLACS). There were no differences in vision, refraction, adverse postoperative events  or  PROMs  between FLACS and CPS groups  at 12 months. Intrastromal FL-assisted astigmatic keratotomies (iFAKs) may provide more effective astigmatic correction compared to LRIs, 12 months post-operatively. 

Date of Award	1 Oct 2021
Original language	English
Awarding Institution	King's College London
Supervisor	David P.S. O'Brart (Supervisor) & Christopher C. Hull (Supervisor)