New Horizons in Cataract Surgery

Cataract surgery has evolved over more than 2000 years. There have been a few pivotal moments in its evolution but in between those developments, the change has been incremental. One of those advances was when an aseptic technique was used and following that when intraocular lenses were designed to be placed inside the eye. Currently there are several new types of development vying to give us another radical change in how we perform cataract surgery and the results that we get for our patients.

During cataract surgery, your natural lens is removed and is replaced with an artificial lens, the intra-ocular lens implant. This is made usually of acrylic and will, if surgery is uncomplicated, last a lifetime.

The optical system of the eye is similar to that of a camera, with a lens at the front and the middle of the eye which focus light onto the film at the back of the eye, the retina. If all is well, the lenses work to focus the incoming light and create a clear image at the back of the eye, however there are a number of factors which can interfere with this.

A cataract is a clouding of the natural lens and if you imagine looking through a foggy bathroom window, that is the effect you might get and the only way to improve vision is to remove and replace the lens with a clear lens.

Eyes can also be poorly focussed with an optical system where light is not focussed clearly onto the back. If the eye is short sighted (myopic), light is focussed in front of the retina and if it is ‘long-sighted’ then light is focussed behind the retina. Added to that, there can be irregularities in the lens at the front of the eye, the cornea, which can cause poor focus also. The cornea can be shaped like a face of a rugby ball rather than a football, and this is called astigmatism. In some cases, this can be treated with a ‘toric’ correction added on to a normal intraocular lens.

When cataract surgery is performed, the cloudy lens is removed and a new lens is placed in the eye. This is placed in a part of the eye called the ‘capsule’ or ‘bag.’ This is the structure that envelopes the natural lens and can be thought of as a clingfilm-like wrapper. When performing cataract surgery, the surgeon tries to preserve this so the new lens can be placed in this part of the eye. It is a perfect location for the new artificial lens as it is transparent, strong, stable, and well positioned to support an optical lens.

Postoperative outcome depends on two factors in cataract surgery: first it is important to perform safe surgery, without complications and second, assuming all goes well, it depends on the accuracy of the lens chosen and the lens itself. The first depends on equipment and surgeon skill and experience, but also on the eye being operated on. A detailed preoperative assessment can pick up eye problems that increase the risk of complication and a tailored approach to surgery means that steps can be taken to make the surgery as safe as possible. For example, for a very dense cataract, a coating can be applied to the inside of the cornea to protect it during surgery, which with a dense cataract can take longer and require more ultrasound energy during phacoemulsification. Ideally, the journey from diagnosis to end result would be carried out by the same person as the preoperative planning can be done in advance. Aftercare is also really important and best done by the operating surgeon as they know best what exactly what steps were taken during surgery.

The other important determinant of postoperative outcome is the lens and biometry (measurements of the eye). Lenses that are placed in the eye are selected to meet certain criteria. They must be inert, remain clear, have a refractive power that is predictable and have optical properties to support vision.

There have been a number of lens technologies that have become available such as toric lenses, multifocal and extended depth of field lenses. However, almost more importantly, there are several new developments in the way we choose what power of lens to use. The lens must have the correct power for the eye to have the desired visual outcome. For example, if you spend your time playing golf, then having the clearest distance vision will be important.

The formulas now available often use artificial intelligence to select the lens we select rather than a simple algebraic formula as previously used. Formulas include the Hill-RBF formula. These more accurately can predict what lens should be used in the eye and results in a better visual outcome.

Traditionally, the (standard single-vision or ‘monofocal’) lens was selected to allow clear focus for distance vision, but not for any other focal points. This usually necessitated ongoing use of glasses for near and mid-vision and often also for distance as the older formulas were not always accurate enough to give a predictable outcome. While glasses are still often required after cataract surgery, the accuracy of the new formulas mean that we have a much more accurate and predictable outcome. This means that more our patients achieve the desired visual outcome and means less adjustment or better contrast after surgery. This could mean the difference between reading the subtitles on the television clearly or being able to jump in the car without needing to find the driving glasses.

Multifocal lenses

Multifocal lenses are lenses that aim to correct vision for both near, mid-distance and distance. They work by using a diffraction grating with rings or zones at three different focal points in the lens. Unlike the natural lens, this lens does not change in thickness, it splits the light three ways to allow the three focal points. These require some time to get used to as the focal points are set and between these points, the vision is blurred. Multifocal lenses do not work for all patients and may cause some visual quality problems such as haloes and glare for example when driving at night.

An example of where this lens has proven useful is for a patient who was still working as a plumber and attended clinic for cataract surgery with three pairs of glasses for near, mid and distance vision. He reported that he would usually lose one of the pairs of glasses and this was affecting his ability to work. He got on very well with the multifocal lenses and now does not need any glasses at any distance after having bilateral uncomplicated cataract surgery.

Extended Depth of Field (EDOF) Lenses

These are the most modern version of the intra-ocular lenses. They offer an increased depth of field allowing good distance and some intermediate vision but no near vision. They do not cause significant glare or haloes like the multifocal lenses, whilst offering a greater depth of field than standard mono-focal lenses. This can be useful for example when wanting to be able to see for distance when driving, but also wanting to be able to clearly see the dashboard without needing glasses. As these do not offer reading vision, a pair of reading glasses will often be required.

This is perhaps the most frequently used ‘premium lens’ for its advantages of an increased depth of field but with almost no disadvantage over the standard single vision lens. Patients report that they can see clearly for distance as well as having a depth of field coming to within arms-length, often allowing screen use without glasses depending on font and screen size.

Monovision or blended vision

This is a method of combining a clearer distance vision lens in one eye with a clearer focus at arms’ length (mid distance vision lens) in the other, is a good option if you are keen to be less glasses-dependent, but it only works if both eyes are healthy, aside from the cataract. A more gradual transition from the far vision in one eye and the mid-distance vision in the other can now be achieved by combining EDOF lenses.

Spreading the focus between the eyes in this way does not normally stop them working together or make you feel unbalanced, and it helps you to do more activities comfortably without glasses. As the brain does the work of choosing the better image so that the better focussed eye is selected, there is a small chance that this arrangement may not be tolerated. Certain tasks will still require ‘top-up’ glasses for at least some activities after surgery and it may take you a few weeks to get used to your new vision. This option requires careful consideration and may not be suitable for all patients.

Summary

Ophthalmology is one of the most technology-driven medical specialties and there are constantly new devices, drugs and software advances appearing. Many of these make cataract surgery quicker, safer, more predictable and with better visual outcomes.

Having some knowledge of the options and being more informed helps your consultant make the right decision for you as the old saying goes that when there are a number of options in medicine, it means there is no ‘best’ option for all and the treatment must be tailored to fit the individual.

Having an understanding of the options is as important for the patient as for their consultant as the choice depends on lifestyle and activities. Furthermore, once cataract surgery has been performed and the lens is in the eye, is it rather more tricky to remove and replace so time spent pondering the choices is better done in advance of surgery and in conjunction with your surgeon.

There are many advances as outlined above and these all make cataract surgery quicker, safer, more predictable and with better visual outcomes. However, some things are unlikely to change, and these are things such as time spent preoperatively with your surgeon. Having that continuity and having the option to discuss your preferences so they match your lifestyle is the gold standard and artificial intelligence or not, the machines will always be limited in their ability to get a feel for what the best option is for the patient.