Deciphering and Understanding IOL Choices: Refractive Cataract Surgery

Dec 17, 2020
17 min read
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As technology has advanced at seemingly warp-speed in cataract 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.

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 Figure 1a-c.(6-8) Figure 1a specifically shows a 1-piece monofocal IOL (this is implanted in the capsular bag), 1b shows a 3-piece monofocal IOL (may be implanted in capsular bag or ciliary sulcus), 1c 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

Multifocal

Multifocal (MFIOL) IOLs provide focusing for at least 2 focal points (e.g. distance and near, or distance and intermediate).1-4,9 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.9,10 As many MFIOLs are manufactured with a diffractive ring design11 (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 night12 (Figure 3). 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.9-14 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.9-14 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 (11)

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Figure 3. Examples of Glare, Halos, and Starbursts (12)

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 (distance-intermediate-near).9,10,13,14 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.9,10,13,14 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).9,10,13-15

Trifocal

Trifocal IOL’s provide patients with vision at near, intermediate and distance.14-16 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.14-16 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.14-16

Extended depth of focus:

Extended depth of focus (EDOF) IOLs aim to provide patients with a functional range of vision (usually excellent intermediate to distance with reasonably good near vision), with a similar visual disturbance profile to a monofocal lens.1,17,18 This is in comparison to MFIOLs, which have specific focal points for near, intermediate, and distance built into their design.1,9,10,17,18 In this way, this subset of IOL’s can offer patients some degree of spectacle independence, with a significantly lower incidence of visual disturbances.1,9,10,17,18 Two different EDOF IOLs are available on the US market at this time: the TECNIS Symfony IOL (Johnson-Johnson Vision, Santa Ana CA) as well as the newer Vivity IOL (Alcon, Fort Worth TX). Both IOLs are manufactured using different optical principles and therefore may offer some advantages in certain patient populations. For example, the Vivity IOL does not utilize diffractive optics in its design, so theoretically it has a lessened incidence of glare and haloes postoperatively—side effects that may still be possible, even with EDOF lenses. 18An example of the Vivity IOL is seen in Figure 4.18

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Figure 4. Vivity Extended Vision IOL (18)

Toric

Toric IOLs correct astigmatism, which is part of the eyeglass prescription.1-3,18,19 If astigmatism is not accounted for/corrected at the time of cataract surgery there is a high chance an eyeglass (or contact lens) prescription for both distance and near will be required postoperatively.19 Toric IOLs are available in monofocal, multifocal and EDOF varieties. Toric lenses typically have markings that are aligned for the patient’s axis of corneal astigmatism. An example of this is seen in Figure 5.20

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Figure 5. Toric IOL with astigmatic markings (20)

Accommodative

Accommodation is the process by which the eye changes optical power/focus to maintain a clear image at varying distances.21 Over time, the ability to accommodate decreases (presbyopia), and it is more difficult to focus at near.21 Accommodative IOLs move or change shape within the eye, allowing for focus at different distances. These IOLs are designed to function much in the same way as the natural lens.21-23 Although there have been several accommodative IOLs in the US market, they are not widely used due to limited accommodative response and unpredictable refractive outcomes. There are some new accommodating IOLs that may appear on the market soon:

The Atia Vision Lens (Atia Vision, Campbell CA): This IOL features a modular, 2-part design, where the back part of the device is a shape-changing implant that is intended to mimic the mechanism used in natural lens accommodation.22,23 This part maintains direct contact with the capsular bag.22 The front (second) section of the device is an exchangeable optic (lens) that is used to address the specific refractive needs of the patient.22 Early preliminary studies have demonstrated this device to show accommodation within the eye. If successful, this IOL has the potential to restore a full range of functional vision to patients.22 The prototype for the Atia device is shown in Figure 6.22

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Figure 6. Atia accommodative lens device (22)

The Opira Lens (ForSight Vision6, Menlo Park, CA): This IOL is a dynamic, shape-changing lens designed for placement in the sulcus with haptic fixation within the capsulorhexis.22 This is in contrast with most other types of IOLs which are usually placed entirely behind the anterior capsulorhexis and in the capsular bag.22 An image of the Opira lens prototype is seen in Figure 7.22

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Figure 7. Opira accommodative IOL (22)

Light adjustable lens:

The first of its kind, the Light Adjustable Lens (LAL, RxSight Aliso Viejo CA) is FDA approved and designed for the treatment of residual refractive error (i.e. eyeglass prescription) that may be present following cataract surgery.24,25 The LAL and corresponding Light Delivery Device are indicated to allow for small adjustments to be made to the IOL power following cataract surgery so that the patient will have better vision when not using glasses.24,25 Until the development of the LAL technology, refractive errors that are common following cataract surgery could only be corrected with glasses, contact lenses, or refractive surgery (e.g. LASIK, PRK). This system provides a new option for certain patients that allows the physician to make small adjustments to the implanted IOL during several in-office procedures after the initial surgery to improve visual acuity without glasses.24,25 The RxSight IOL is made of a unique material that reacts to UV light, delivered by the corresponding light delivery device, 17-21 days post-surgery.24,25 Patients receive 3-4 light treatments over a period of 1-2 weeks, each lasting 40-150 seconds, depending on the amount of adjustment needed.24,25 The patient must also wear special UV-blocking eyeglasses from the time of cataract surgery to the end of light treatments to protect the new lens from UV light in the environment. Figure 8 demonstrates the LAL as well as its theorized mechanism.25

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Figure 8. Light Adjustable Lens before and after UV treatment (25)

New technologies on the horizon

Pin-hole IOL: A novel type of IOL, the pinhole IOL Is based on the stenopeic principle, which allows small central rays to enter the eye and eliminates diverging rays, thus reducing the circle of blur on the retina.26,27 As a result of this, depth of focus is increased, providing patients with good distance and near vision.26,27 Currently, 2 types of pinhole-based IOLs exist, though neither is yet approved for use in the USA (IC-8 IOL, Acufocus, Irvina CA), and Xtrafocus IOL (Morcher, Germany (Figure 9)).28-33 Though both of these IOLs have shown to increase depth of focus, and can provide this in patients who may not be good candidates for MFIOLs, these IOL’s can have a disadvantage, such as decreased brightness, decreased visual field and decreased optimal visual acuity.28-33 In addition, patients with certain eye conditions, such as central corneal scarring, large pupils (>6mm), severe glaucoma, severe macular pathology are not good candidates for pinhole IOLs.28-33