Set reasonable patient expectations for presbyopia treatment
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With refractive cataract surgery, we have the ability to treat large degrees of refractive errors at the same time that we remove the cataract. We can treat a wide range of hyperopia, myopia and even astigmatism.
However, when it comes to treating presbyopia, our surgical solutions simply cannot deliver the accommodation of youth. It is important that our patients understand the limitations of current technologies in the treatment of presbyopia so that their expectations can be set appropriately.
Because we do not yet have a commercially available, truly accommodating IOL, we address presbyopia with alternative methods. We can employ monovision in which we choose a different refractive target for each eye in order to expand the range of spectacle-free vision. While this takes some getting used to, it provides high-quality vision for the desired ranges. There can be some limitation in depth perception, and glasses may still be needed for optimal stereoscopic vision such as for night driving.
We have seen many different bifocal or multifocal IOL designs over the past few decades. The refractive designs have been phased out in favor of diffractive ring models that split the incoming light into zones to cover both distance and near vision. However, with the diffractive rings, there are some compromises. First, a small amount of the incoming light is lost, and then there are inevitable halos and glare that occur at night. These tend to become less noticeable with time as the brain adapts to the new vision and filters out some of this effect. We now use primarily trifocal IOL designs that use diffractive rings to produce a wide range of vision covering the three main zones: distance vision (1 m to far away), intermediate vision (0.5 m to 1 m) and near vision (closer than 0.5 m).
Extended depth of focus (EDOF) designs aim to elongate the focal zone to provide distance and intermediate zones of vision without glasses. Older EDOF designs used diffractive rings to accomplish this, but that was associated with nighttime dysphotopsias such as glare, halos and even a spiderweb effect. Newer EDOF designs use a central beam-shaping element instead to give a similar wide range of uncorrected vision but without the night glare and halos. These newer EDOF designs still come with a mild compromise, which is decreased contrast, particularly at night.
The main concept to understand with all of these IOL designs is that the number of photons of light entering the eye is going to be the same. You can use a monofocal IOL to concentrate all the photons on one range such as distance vision and then employ spectacles to shift all the photons to give intermediate or reading vision. This produces the highest quality of vision with the best night vision; however, it requires the use of glasses for computer work, cell phone use and reading.
If we choose a modern-design EDOF IOL with a central beam-shaping element, we are going to shift the distribution of those incoming photons over a wider range. This means taking away some of the light energy from distance vision and sending it to the intermediate vision range. This will result in a mild to moderate decrease in contrast for distance vision, which may be noticeable primarily at night. For most of our cataract patients, the resultant night vision will be better than their existing night vision, so this is not an issue.
The trifocal IOL designs split the incoming light into all three zones, which comes with a compromise in terms of image quality. When comparing these IOL designs, we must always remember that the total number of photons entering the eye is the same. All we can do is change how we distribute the light energy. When we graph these (Figure 1), we also note that the area under each curve is the same. The trifocal IOLs also induce night glare and halos due to the nature of the diffractive rings.
Source: Uday Devgan, MD
When we set patient expectations, we need to emphasize that there is a trade-off between image quality and the range of vision without glasses. If the patient demands the highest quality of vision for night driving, then our EDOF and trifocal IOL designs will likely fall short in meeting expectations. If the patient is presenting to us with visually significant cataracts, then our job is easier because any of these IOL designs will likely produce better quality of vision than the patient currently has.
The toughest situation is patients who are presbyopic with a plano refraction and minimal to no cataractous changes. These patients are seeking a surgical solution for presbyopia, but our current technology may not be able to give them the desired visual outcome. In the future, with truly accommodating IOL designs, we will be able to satisfy these patients, but for now, let’s do our best to underpromise and then overdeliver.
See full video of this case at cataractcoach.com.
- For more information:
- Uday Devgan, MD, is in private practice at Devgan Eye Surgery, Chief of Ophthalmology at Olive View UCLA Medical Center and Clinical Professor of Ophthalmology at the Jules Stein Eye Institute, UCLA School of Medicine. He can be reached at 11600 Wilshire Blvd. #200, Los Angeles, CA 90025; email: devgan@gmail.com; website: www.CataractCoach.com.
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