Abstract:
Cataract is an extremely common natural ageing phenomena with the majority of the elderly population having a degree of cataract formation. As the human crystalline lens develops cataract, it is accompanied by a commensurate reduction in visual acuity with variable loss of and disturbance of vision. Therefore, cataract surgery is common in the older population, indeed, cataract surgery is the most common surgical procedure in the world! Contemporary cataract surgery typically uses ultrasound in the removal of the cataract, in a technique called phacoemulsification, which is usually performed with local anaesthetic and via a small, suture-less, corneal incision. The vast majority of cataract surgery procedures result in significant restoration of vision to the patient. However, even the most skilful procedures can be associated with unwanted complications. This series of interrelated studies was developed to understand and report on complications of cataract surgery in a New Zealand public teaching hospital environment, where trainee surgeons develop their key skills to provide cataract surgery in the future. This thesis covers the basic anatomy, physiology and optics of the eye, with definitions of cataract and its aetiology. It also briefly outlines the evolution of cataract surgery before providing a considered review of what constitute the key complications that are encountered in contemporary cataract surgery. Two major prospective clinical studies are thereafter reported on the application of a new preoperative cataract risk stratification tool, the New Zealand Cataract Risk Stratification (NZCRS) system, developed by the author and colleagues. In the first of these studies, 500 consecutive cases of phacoemulsification cataract surgery were prospectively categorised using the NZCRS system and apportioned to either junior or more experienced cataract surgeons based on a cut-off threshold score. This study demonstrated a 40% decrease in intraoperative complications compared to baseline studies. In a second study, the NZCRS system was applied to a further cohort of 500 consecutive cataract phacoemulsification procedures as the ‘standard of care’ i.e. the scoring system and its application were conducted by the surgeons in the public hospital service without direct intervention of the investigator. This study demonstrated more than 80% uptake by the surgeons, with 99% adherence to the scoring system recommendations, and convincingly maintained a greatly reduced cataract surgery intraoperative complication rate. These studies were also used to assess postoperative complications prospectively in 1000 cases, and this identified cystoid macular oedema as the most common postoperative complication affecting more than 3% of cases, whether there were intraoperative complications or not. Therefore, the final study of this thesis is a major review of contemporary literature on pseudophakic cystoid macular oedema to further delineate its aetiological features, diagnosis, and best therapeutic interventions. Overall, these four inter-related reviews and prospective clinical studies clearly demonstrate that complications in contemporary phacoemulsification cataract surgery are fortunately relatively uncommon, but promisingly these complications can be reduced significantly by utilisation of preoperative cataract risk stratification systems, such as the newly developed New Zealand Cataract Risk Stratification system.