A Randomised, Controlled Study to Compare Visual Performance Following Bilateral, Micro-monovision Insertion of Two Toric, Aspheric, Hydrophobic Acrylic Intraocular Lenses: The TECNIS Eyhance Toric II IOL and the Alcon Acrysof IQ Toric IOL

Cataract is a condition caused by progressive clouding of the natural crystalline lens inside the eye. This leads to impairment of visual performance. This condition represents a huge disease burden and is a leading cause of reversible blindness worldwide. In the UK and the developed world, the incidence of cataract induced blindness continues to increase, secondary to an aging population and increasingly common risk factors such as diabetes. In 1950, Harold Ridley inserted an intraocular lens following cataract extraction at St Thomas' Hospital. This was the first recorded surgery of its kind, and heralded the development of modern cataract surgery, which is comprised of extraction of a cataract by phacoemulsification (ultrasonic micro-fragmentation) followed by insertion of a foldable intraocular lens. Cataract surgery (CS) is the most common elective surgical procedure in the developed world, and the most common in the EU, with 4 million procedures performed in 2016. CS continues to evolve, as do intraocular lenses (IOLs).

Currently, only mono-focal (one point of focus) IOLs are available during cataract surgery in the NHS. These are designed to give excellent vision for one fixed point of focus (either distance, intermediate or near vision), with most patients opting for good distance vision, and requiring glasses for intermediate vision or near vision. Accordingly, these lenses do not treat presbyopia, the loss of the ability focus on near objects, that most people develop in their 50's. In addition, the standard monofocal lens does not treat astigmatism, a common condition characterized by a non-spherically shaped cornea (the clear tissue at the front of the eye) which results in blurred unaided distance and near vision and the need for both reading and distance glasses following surgery.

In this trial patients will be randomly assigned to receive two TECNIS Eyhance Toric lenses or two Alcon Acrysof IQ Toric II lenses (one for each eye). Prior to surgery the 'power' of each patients intraocular lens is chosen. This is similar to choosing the power of lenses in spectacles at an opticians. By choosing the power of one eye to be targeted for distance and the other offset for a small myopic (short-sighted) correction to allow unaided intermediate (computer) and some unaided near vision, the investigators can then investigate the efficacy of these lenses not only to improve vision after cataract surgery but also their ability to treat astigmatism and reduce the dependence on spectacles following NHS CS. As such the investigators hope to offer cost benefits to NHS patients as well as quality of life improvements. In addition to efficacy, quality of life and cost benefits to patients, the investigators will also explore patient acceptability of such "premium" IOLs and look at models to investigate their affordability with the NHS setting.

This study is a clinical trial, designed to compare visual outcomes after cataract surgery with two different intraocular lenses. As previously described, modern day cataract surgery is composed of two main components: removal of the cataract, and insertion of an intraocular lens (IOL). The role of the intraocular lens is to replace the focusing power of the natural crystalline lens inside the eye. It is this lens that becomes a cataract. Removing a cataract alone helps light enter the eye, but does not focus it well. Prior to the invention of intraocular lenses, patients required extremely thick and strong glasses for both distance vision.

Currently only monofocal intraocular lenses are available on the NHS. Different strengths of lens can be chosen to give the patient good distance, intermediate or near vision. That means the ability to focus on objects in the distance, middle distance or near. Most patients opt for good distance vision, enabling them to mobilise easily, watch TV and drive, and require glasses for reading.