Refractive Lens Exchange

Introduction to RLE

IOL Surgery: What is it?

IOL surgery also known as refractive lens exchange (RLE) or natural lens replacement (NLR). It is similar to cataract surgery however, it is performed at an earlier stage before a cataract has developed in order to minimise patients dependence on spectacles. It is now increasing in popularity and it is only second to LES as the most common elective surgery with millions of happy patients worldwide. RLE works by exchanging the natural and increasingly dysfunctional lens of the eye called crystalline lens for a permanent plastic one that has the correct power and optical quality to give some form of spectacle independence. The general result is a more natural spectacle free vision for many years to come.

What types of IOLs exist?

RLE employ a wide array of IOLs depending on the patient requirements: level of prescription, the presence of corneal scars, previous eye surgery, pupil size, age of patient, occupation, lifestyle, presence of medical condition like Diabetes, Glaucoma, Macular degeneration etc. Some of the common IOL types are listed below.

• Monofocal: A monofocal lens uses a high precision optic to focus all light passing through the pupil to one focal point, this can be either near or distance or in between depending on Px requirements. (Tecnis ZA, ZCB, Sensar AR40e)
• Multifocal (bifocal, trifocal, sectoral, refractive, diffractive): To be a good candidate you need to already have a significant visual handicap and be a positive person seeing a glass half full as opposed to half empty and do not suffer from diabetes, macular pathologies or states like anxiety, depression, OCD or bipolar. These lenses can be viewed in lay terms as light splitters that some light does the distance and the rest does the near and/or intermediate vision. So, a weak MF lens vs intermediate vs strong lens would split the light to 80-20% vs 75-25% vs 55-45% for distance and near vision respectively. This is the only lens type that induces many images simultaneously and requires a significant brain adaptation that more than 90% of the general population can manage, especially the younger patients. Examples: Tecnis Symfony, Tecnis ZLB and ZKB, SBL-3, PhysIOL, Zeiss trifocal, Lentis M+ or Mx
• Tecnis Symfony: This is a new concept lens called Extended Depth-of-Focus (EDOF) IOL. The Symfony takes a different approach to maximizing a patient’s range of vision by addressing the optical property known as chromatic aberration. The idea behind chromatic aberration correction is simply to get the colors of the spectrum focused at the same point. “The different colors of the spectrum focus differently. Different materials have different dispersive properties with light; some focus colors closely together and some spread them out. The idea is that if you focus all of the colors together, you can have a higher quality of vision. The Symfony takes the AMO acrylic that focuses colors well—meaning it has a low dispersion—and improves upon it. This gives cataract patients a somewhat expanded depth of field without the drawbacks associated with a multifocal visual system. The EDOF lens will perform better at near distances than the monofocal, but not as well at near as the multifocal. But, halos and glare will be comparable to the monofocal.To understand how the Symfony can give more depth of field, it helps to understand the natural steps of accommodation, because the lens actually builds on them to get its effect. When we look up close, we experience the depth-of-field effect. Our pupils constrict giving us the equivalent of about 0.75 to 1 D more near vision than we’d have when looking into the distance because of the pinhole effect. Building on this natural accommodative effect, the Symfony uses diffractive optics to both improve the quality of vision from the lens and expand the range of distances the lens at which the lens can adequately focus. The first thing to understand is that the term diffractive optics doesn’t necessarily imply multifocality. This is not a multifocal lens, but it does use diffractive optics to do two things: First, it corrects chromatic aberration. Second, it uses these optics to extend the range of quality vision. With optics you can’t gain an expanded range of vision without losing something in terms of the sharpness of vision. However, by correcting chromatic aberration, even without using diffractive optics to expand the visual range, the lens would have extremely sharp distance vision on the order of 20/12 or even 20/10. The process is not yet done, however, in the Symfony. The diffractive optics are then used to expand the range of vision. Expanding the depth of focus degrades the tack-sharp “starting point” (something must be lost), but since the lens started with such sharp vision, it only degrades to about the level of 20/20. So the amount you degrade takes you back to the level of a good monofocal IOL.
  Average study results indicate that the Symfony gives 20/20 or better vision at distance over a range of about 1.5 D, and 20/40 or better over a range of 2.5 D. 96% of patients had 20/25 or better vision at intermediate and 92% had 20/40 or better vision for near. In terms of quality of vision, it’s comparable to a monofocal from a night vision and a contrast sensitivity perspective. For more information and to see how the lens was developed have a look in my Blog
• Accommodating: This is the only lens type that tries to utilise the function of the eye as a focusing apparatus. On principle this is a monofocal lens that has the ability due to it’s design to move a bit inside the eye thus improving the depth of focus however, such movement is not sufficient for full spectacle independence and may wean over time. It will require yag laser well before other lens types. Examples: Tetraflex HD (by Lenstec)

Tetraflex HD Accommodating lens by Lenstec