The Ultimate Guide to the Most Commonly Used IOLs

Nov 8, 2021
30 min read
3.3k views
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As technology has advanced at seemingly warp-speed in cataract surgery and refractive surgery, so has our expanded intraocular lens (IOL) options available to cataract surgery patients.

However, the vast choices available can sometimes be overwhelming, and it is important to provide pre-surgical patients with a clear understanding of what cataract surgery is, and how we can improve and enhance their vision with new and advanced technology—intraocular lens implants.

This article outlines some of the more common IOL technologies available and their specifics.

Why is intraocular lens implantation necessary?

An intraocular lens, with respect to cataract surgery, is an artificial lens that is placed into the eye at the time of cataract extraction.1-3 The IOL replaces the eye’s natural lens that is removed during the surgery. The natural crystalline lens inside the eye bends (refracts) light to allow for clear images.1-3 However, as a cataract forms (i.e. the lens becomes cloudier), images seen become gradually hazier and dimmer in nature.

Therefore, cataract surgery removes this natural cloudy lens and replaces it with a clear IOL to help enhance and improve vision.1-3 Cataract extraction without implantation of an IOL (i.e., aphakia) can lead to very blurry vision, and the need for incredibly high prescription (“coke-bottle”) eyeglasses or contact lenses, which can be very difficult to tolerate.

Therefore, standard-of-care cataract surgery always includes intraocular lens implantation during the procedure. In general, routine cataract surgery involves IOL implantation within the capsular bag complex; less commonly the IOL may be implanted in the ciliary sulcus or anterior chamber.1-3

IOLs come in different focusing powers—similar to prescription eyeglasses or contact lenses. The correct power IOL for the eye is determined by extensive measurements and calculations performed at the time of cataract evaluation.1-3 Most IOLs are composed of acrylic or silicone materials—these are biocompatible and are not rejected by the body once implanted. Some IOLs are also coated with a special UV-blocking material to help protect from harmful UV rays.1-3 Below we review the different types of IOLs available.

IOL Categories

Monofocal

The most common type of lens used with cataract surgery is a monofocal IOL. Monofocal means “one focal point” or “one focus”. It is therefore set to focus for distance, intermediate, or near only (but not all three).1-4 Most patients who choose monofocal IOL’s choose distance correction, and therefore use glasses for reading, working on a computer, and other near activities postoperatively.

Alternatively, patients may also choose to have monovision, where one eye (typically the dominant eye) is corrected for distance, and the other eye is corrected for near, providing a range of vision from near to distance.1-5 It is recommended that patients trial monovision with contact lenses prior to making the decision to have cataract surgery with monovision to ensure they can tolerate it. Not all patients like monovision and they may have altered depth perception that could affect their ability to safely navigate walking up and down stairs.1-5

An example of what monofocal IOLs look like is seen in the figure below. Figure 1a (far left) specifically shows a 1-piece monofocal IOL (this is implanted in the capsular bag), Figure 1b (center) shows a 3-piece monofocal IOL (may be implanted in capsular bag or ciliary sulcus), and Figure 1c (far right) shows an example of an anterior chamber (ACIOL) IOL.

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Figure 1a. Single-piece IOL6 - Figure 1b. 3-piece IOL7 - Figure 1c. ACIOL8

  • Varieties (There are several brands available in the USA: Alcon (Fort Worth TX), Johnson & Johnson Vision(Jacksonville FL), Bausch + Lomb (Bridgewater NJ), BVI (Waltham, MA))
    • Single-piece IOLs: this is implanted in the capsular bag only. 1-3 An illustration of a single-piece IOL is seen in Figure 1a.
    • 3-piece IOLs: typically has an acrylic or silicone optic with thin PMMA, polypropylene, or polyvinylidene fluoride (PVDF) haptics that may be implanted in the capsular bag, ciliary sulcus, or scleral fixated. 1-3, 6 An illustration of a 3-piece IOL is seen in Figure 1b.
    • Anterior chamber IOLs (ACIOL): these are 1-piece IOLs meant to be implanted in the anterior chamber and rest on the iris. It is essential to create a peripheral iridotomy/iridectomy at time of insertion to prevent pupillary block. These IOLs cannot be folded at time of insertion and typically require a 6mm incision size that is sutured closed.1-3
  • Expected Visual Acuity: Most patients who choose monofocal IOLs choose distance correction, and therefore use glasses for reading, working on a computer and other near activities postoperatively. Alternatively, patients may also choose to have monovision, where one eye (typically the dominant eye) is corrected for distance, and the other eye is corrected for near, providing a range of vision.1-3
  • Mechanism of Action: Provides “one focal point” or “one focus”. It is therefore set to focus for distance, intermediate or near only (but not all three). The focal point, and therefore IOL power, is calculated and chosen by the surgeon and patient prior to surgery.1-3
    • Allows maximum amount of light through to the retina with minimal light energy lost in comparison to multifocal IOLs1-3
  • Ideal Patient Candidates: All patients are considered good candidates for monofocal IOLs; these lenses have minimal side effects and generally provide the sharpest vision and contrast sensitivity.1-3
  • Side effect profile: Minimal risk of glare/haloes
    • Standard risk of visual aberrations with IOL decentration or other surgical complications
  • Relevant FDA data: IOLs should be used as specified (e.g., no single-piece IOL’s in the sulcus!)

Multifocal

Multifocal (MFIOL) IOLs provide focusing for at least two focal points (e.g. distance and near, or distance and intermediate).1-4,10 These IOLs decrease the need for glasses postoperatively by providing good vision across a range of distances. The lens has special zones set at different powers to allow for an enhanced range of vision.10,11 As many MFIOLs are manufactured with a diffractive ring design12 (Figure 2), it is possible that some patients may experience side effects, such as glare, haloes, or starbursts around bright lights—most commonly while driving at night.13

In addition, in an attempt to provide a full range of vision, the diffractive ring design can lead to a compromise in contrast sensitivity—or how sharply images are seen.10-15 Therefore, it is usually not recommended to implant MFIOLs in patients with advanced macular degeneration, glaucoma, and other retinal diseases that already cause compromised visual acuity.10-15

Technology surrounding multifocal IOLs has advanced significantly, and it is much less common for patients to experience severe visual adverse effects from newer lenses, however, it is certainly something to be aware of and imperative to include in the consent process.

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Figure 2. Diffractive IOL Design (12)

Traditionally, MFIOLs in the USA were bifocal lenses—permitting vision at distance and near, or distance and intermediate but not all three focal points (distance-intermediate-near).10,11,14,15 Though these IOLs function well, some patients realized that they were “missing part of their vision” (i.e. in bilateral distance-near or bilateral distance-intermediate IOL implantation), and this lead to surgeons using a mix-and-match technique to help provide patients with a full range of vision from near to intermediate to distance.10,11,14,15

This would be done by placing a “distance-near” MFIOL in one eye and a “distance-intermediate” IOL in the other. Though this worked well in some patients, a true “full range of vision” from an IOL did not come about until a trifocal lens was introduced in the US in 2019 (PanOptix, Alcon, Fort Worth TX).10,11,14-16

Trifocal IOLs provide patients with vision at near, intermediate and distance.15-17 There is one trifocal IOL FDA approved in the US at this time (PanOptix) and many patients have been incredibly happy with its visual results.15-17 However, it is important to note that it is still possible to have glare, halos, and starbursts with these IOLs, although the PanOptix lens has reportedly less incidence of this compared to the early iterations of bifocal IOLs.15-17

  • Varieties
    • Bifocal: Traditionally, MFIOLs in the USA were bifocal lenses—permitting vision at distance and near, or distance and intermediate but not all three focal points (i.e., distance-intermediate-near)1-5,14, 16-17
      • Available in Toric and Spherical versions
    • Trifocal: These IOLs provide patients with vision at near, intermediate and distance. There are two trifocal IOLs FDA approved in the US at this time (PanOptix, Alcon, Fort Worth TX and TECNIS Synergy, Johnson & Johnson Vision, Jacksonville FL)1-5, 14, 16-17
      • Note: The Synergy IOL is a combination of a multifocal IOL and extended depth of focus technology, thereby combining two mechanisms to provide an extended range of vision.
      • Available in toric and spherical versions
  • Expected Visual Acuity: These IOLs decrease the need for glasses postoperatively by providing good vision across a range of distances. However, patients should be advised that very fine work, or near work done at a short distance from their face may still require reading glasses (generally at a distance closer than 40cm).1-3,4-5,10-16
  • Mechanism of Action: Multifocal (MFIOL) IOLs provide focusing for at least 2 focal points (e.g. distance and near, or distance and intermediate). The lens has special zones set at different powers to allow for the enhanced range of vision.1-3, 4-5,10-17
    • Diffractive optics (in brief): Bifocal and Trifocal IOLs generally work via diffractive optics which take advantage of the wave-nature of light and constructive as well as destructive interference. Waves of light also undergo diffraction when they interact with boundaries and sharp edges (i.e., rings on an IOL optic)—this causes the light to bend around the edges and travel in a different direction. In diffractive MFIOLs, a specifically shaped structure is usually placed on the lens surface that intentionally induces diffraction so that waves exiting the lens will have constructive interference at 2 (or more) distinct foci.18 An illustration of diffractive IOL technology is seen in Figure 3.
  • Ideal Patient Candidates: Due to potential side effect profile (i.e., glare, haloes, decreased contrast sensitivity), MFIOLs are usually not recommended in patients with advanced macular degeneration, glaucoma, corneal dystrophies and other ocular diseases that already cause compromised visual acuity. 1-3, 4-5,10-17
  • Side Effect Profile: As many MFIOLs are manufactured with a diffractive ring design, it is possible that some patients may experience side effects, such as glare, haloes, or starbursts around bright lights—most commonly while driving at night. In addition, in an attempt to provide a full range of vision, the diffractive ring design can lead to a compromise in contrast sensitivity—or how sharply images are seen. Technology surrounding multifocal IOLs has advanced significantly and it is much less common for patients to experience severe visual adverse effects from newer lenses, however, it is certainly something to be aware of and imperative to include in the consent process.1-3, 4-5,10-17
  • Relevant FDA Data: Multifocal IOLs (bifocal and trifocal varieties) have been FDA approved for surgically naïve (e.g. no prior LASIK, PRK, RK, other corneal surgeries, etc) eyes. Certain IOLs have been studied in post-refractive surgery patients (phase IV, post-market studies), however, caution is advised in any patients with significant corneal pathology, or disease states that can predispose to poor visual outcomes (e.g., severe pseudoexfoliation, glaucoma, macular degeneration, etc).1-3, 4-5,10-17