Having to frequently take reading glasses on and off is inconvenient for many people. Because of this, a person might wear reading glasses around their neck, scatter multiple pairs around the house or wear bifocals all the time. With today’s advanced lens procedures, patients now have a choice in the type of lens that is implanted during cataract or clear lens extraction surgery. Unlike conventional ”single vision” intraocular lenses (IOLs), extended depth of focus IOLs are lens implants that are designed to help patients see at varying distances, providing an extended range of vision. The goal of an EDOF IOL (Tecnis® Symfony IOL, Abbott Medical Optics, Santa Ana, CA) to provide functional, high quality vision from far distance to about 26 inches to minimize the use of glasses. Although they might still prefer to wear glasses for prolonged reading, the vast majority of EDOF IOL patients experience freedom from glasses for tasks such as driving, watching TV, using their cell phone and computer, looking at photos, reading magazines, price tags, product labels, receipts, and menus.
How Does an Extended Depth of Focus IOL Work?
Tecnis® Symfony IOL (Abbott Medical Optics)
With bifocal glasses, a person initially needs to think about looking through the top part of the lens for distance and through the bottom part of the lens for near. An Extended Depth Of Focus (EDOF) IOL, designed using advanced technology called diffractive optics, is entirely different, providing a continuous range of vision from distance to near seamlessly, not requiring any thought from the patient. There is no learning curve for using these new advanced optics, unlike the learning process a person goes through when first wearing bifocal or progressive spectacles. The Tecnis ® Symfony IOL uses proprietary optic technology to create high quality vision across a range from distance to about 26 inches away. The technology used is much like that used in the highest quality professional camera lenses, to dramatically reduce a phenomenon called chromatic aberration. You may recall from grade school how a prism separates light into the colors of the rainbow. This same effect occurs with the natural lens of the eye and with intraocular lens implants used for cataract surgery. Chromatic aberration degrades the quality of vision. The Symfony IOL has a level of chromatic aberration so low it is below even what is seen with the healthiest of young human lenses. The technology also uses diffractive optics to bring light to a focal range, not a single point. The result is high quality vision, without glasses, across a wide range of distances.
Chromatic aberration degrades image quality, causing blurring and color “fringing” at edges.
High performance photographic camera lenses use diffractive optics to reduce chromatic aberration and improve image quality. The Tecnis® Symfony IOL uses very similar optics to provide high quality vision to cataract patients.
Tecnis Symfony IOL uses proprietary achromatic technology to counteract the chromatic aberration caused by the human cornea, resulting in sharper image quality and improved vision compared to IOLs without chromatic aberration correction.
Are There Side Effects?
Depending on pupil size, the EDOF IOL patient may experience some halos, glare or starbursts around lights at night. These halos are different from and much less problematic than those typically caused by cataracts. These halos become less noticeable and distracting over time as the brain learns to selectively ignore them through a process called neuroadaptation. This is the same process that allows us to ignore background noise such as traffic sounds or an air conditioning fan. How quickly these adjustments are made by the brain varies for different individuals. Experience has shown that neuroadaptation is a gradual process that occurs over several months. Halos are often quite noticeable during the first 24 hours after surgery when the pupil is still dilated from medication. Do not be alarmed or misled by this temporary situation. Compared to their predecessors, the current EDOF IOLs have been engineered to significantly reduce the halo effect.
Will I Need Additional Procedures to Achieve the Best Result?
Much like contact lenses or glasses, an EDOF IOL comes in more than 60 different “powers”. As with prescription eyeglasses or contact lenses, it is important to match the appropriate IOL power to your eye. When prescribing eyeglasses or contact lenses, we utilize trial and error to preview different lens powers to determine which one you see best with (“Which one is better, one or two?”). However, because the EDOF IOL is implanted inside the eye, and only after your natural lens (cataract) has been removed, it is impossible for you to “preview” various IOL powers prior to surgery. Furthermore, once it is implanted we cannot as easily exchange the IOL as we could with glasses or contact lenses. Fortunately, an appropriate IOL power can be estimated using advanced mathematical formulas based on pre-operative measurements of your eye’s dimensions. Although these formulas are quite accurate in most patients, there are individual variables that prevent this process from being 100% perfect. In particular, individuals who are extremely nearsighted, farsighted, or have high amounts of astigmatism, and patients who have had previous refractive surgery (e.g. RK, PRK, LASIK), are more likely to end up with an IOL power that is not optimal because the mathematical formulas are based on average sized eyes, not extremes or eyes that have had previous surgery. EDOF IOLs are high performance devices and, accordingly, require precisely tuned optics. If the IOL power is not optimal, the EDOF IOL will not perform as well as desired. In these situations, a patient may discover the vision is adequate for most tasks and that wearing a very thin pair of glasses helps them out in certain situations (e.g. night driving or reading). Alternatively, an additional procedure, such as LASIK or PRK, can be performed to optimize the outcome. There is a 15% chance that a secondary procedure like LASIK will be necessary to fine tune the spectacle free vision.
Alternatives to EDOF IOLs
Alternatives to an EDOF lens include monofocal, multifocal, or accommodative IOLs. A patient who chooses a monofocal (conventional single vision) IOL implanted for distance vision must be aware that glasses for near vision will be necessary. To reduce dependence on glasses for near vision tasks, monovision correction with monofocal IOLs is also an option. Monovision correction is a technique that makes use of the fact we have two eyes. In this technique, one eye is implanted for distance vision while the other is implanted for near vision. After an adjustment period which usually lasts several weeks, the brain neuroadapts to this new optical arrangement, allowing the patient to see far and near seamlessly. This monovision arrangement is often used in patients who wear contact lenses in a monovision set up full time and who are over the age of 45. Monovision may not be the best choice for all patients.